zig

blob 4770da76 (176442B) - Raw

---

 const Wasm = @This();
 
 const std = @import("std");
 
 const assert = std.debug.assert;
 const build_options = @import("build_options");
 const builtin = @import("builtin");
 const codegen = @import("../codegen.zig");
 const fs = std.fs;
 const leb = std.leb;
 const link = @import("../link.zig");
 const lldMain = @import("../main.zig").lldMain;
 const log = std.log.scoped(.link);
 const mem = std.mem;
 const trace = @import("../tracy.zig").trace;
 const types = @import("Wasm/types.zig");
 const wasi_libc = @import("../wasi_libc.zig");
 
 const Air = @import("../Air.zig");
 const Allocator = std.mem.Allocator;
 const Archive = @import("Wasm/Archive.zig");
 const Cache = std.Build.Cache;
 const CodeGen = @import("../arch/wasm/CodeGen.zig");
 const Compilation = @import("../Compilation.zig");
 const Dwarf = @import("Dwarf.zig");
 const File = @import("Wasm/file.zig").File;
 const InternPool = @import("../InternPool.zig");
 const Liveness = @import("../Liveness.zig");
 const LlvmObject = @import("../codegen/llvm.zig").Object;
 const Module = @import("../Module.zig");
 const Object = @import("Wasm/Object.zig");
 const Symbol = @import("Wasm/Symbol.zig");
 const Type = @import("../type.zig").Type;
 const TypedValue = @import("../TypedValue.zig");
 const Value = @import("../value.zig").Value;
 const ZigObject = @import("Wasm/ZigObject.zig");
 
 pub const Atom = @import("Wasm/Atom.zig");
 pub const Relocation = types.Relocation;
 
 pub const base_tag: link.File.Tag = .wasm;
 
 base: link.File,
 /// Symbol name of the entry function to export
 entry_name: ?[]const u8,
 /// When true, will allow undefined symbols
 import_symbols: bool,
 /// List of *global* symbol names to export to the host environment.
 export_symbol_names: []const []const u8,
 /// When defined, sets the start of the data section.
 global_base: ?u64,
 /// When defined, sets the initial memory size of the memory.
 initial_memory: ?u64,
 /// When defined, sets the maximum memory size of the memory.
 max_memory: ?u64,
 /// When true, will import the function table from the host environment.
 import_table: bool,
 /// When true, will export the function table to the host environment.
 export_table: bool,
 /// Output name of the file
 name: []const u8,
 /// If this is not null, an object file is created by LLVM and linked with LLD afterwards.
 llvm_object: ?*LlvmObject = null,
 /// The file index of a `ZigObject`. This will only contain a valid index when a zcu exists,
 /// and the chosen backend is the Wasm backend.
 zig_object_index: File.Index = .null,
 /// List of relocatable files to be linked into the final binary.
 files: std.MultiArrayList(File.Entry) = .{},
 /// When importing objects from the host environment, a name must be supplied.
 /// LLVM uses "env" by default when none is given. This would be a good default for Zig
 /// to support existing code.
 /// TODO: Allow setting this through a flag?
 host_name: []const u8 = "env",
 /// List of all symbols generated by Zig code.
 synthetic_symbols: std.ArrayListUnmanaged(Symbol) = .{},
 /// Maps atoms to their segment index
 atoms: std.AutoHashMapUnmanaged(u32, Atom.Index) = .{},
 /// List of all atoms.
 managed_atoms: std.ArrayListUnmanaged(Atom) = .{},
 /// Represents the index into `segments` where the 'code' section
 /// lives.
 code_section_index: ?u32 = null,
 /// The index of the segment representing the custom '.debug_info' section.
 debug_info_index: ?u32 = null,
 /// The index of the segment representing the custom '.debug_line' section.
 debug_line_index: ?u32 = null,
 /// The index of the segment representing the custom '.debug_loc' section.
 debug_loc_index: ?u32 = null,
 /// The index of the segment representing the custom '.debug_ranges' section.
 debug_ranges_index: ?u32 = null,
 /// The index of the segment representing the custom '.debug_pubnames' section.
 debug_pubnames_index: ?u32 = null,
 /// The index of the segment representing the custom '.debug_pubtypes' section.
 debug_pubtypes_index: ?u32 = null,
 /// The index of the segment representing the custom '.debug_pubtypes' section.
 debug_str_index: ?u32 = null,
 /// The index of the segment representing the custom '.debug_pubtypes' section.
 debug_abbrev_index: ?u32 = null,
 /// The count of imported functions. This number will be appended
 /// to the function indexes as their index starts at the lowest non-extern function.
 imported_functions_count: u32 = 0,
 /// The count of imported wasm globals. This number will be appended
 /// to the global indexes when sections are merged.
 imported_globals_count: u32 = 0,
 /// The count of imported tables. This number will be appended
 /// to the table indexes when sections are merged.
 imported_tables_count: u32 = 0,
 /// Map of symbol locations, represented by its `types.Import`
 imports: std.AutoHashMapUnmanaged(SymbolLoc, types.Import) = .{},
 /// Represents non-synthetic section entries.
 /// Used for code, data and custom sections.
 segments: std.ArrayListUnmanaged(Segment) = .{},
 /// Maps a data segment key (such as .rodata) to the index into `segments`.
 data_segments: std.StringArrayHashMapUnmanaged(u32) = .{},
 /// A table of `types.Segment` which provide meta data
 /// about a data symbol such as its name where the key is
 /// the segment index, which can be found from `data_segments`
 segment_info: std.AutoArrayHashMapUnmanaged(u32, types.Segment) = .{},
 /// Deduplicated string table for strings used by symbols, imports and exports.
 string_table: StringTable = .{},
 
 // Output sections
 /// Output type section
 func_types: std.ArrayListUnmanaged(std.wasm.Type) = .{},
 /// Output function section where the key is the original
 /// function index and the value is function.
 /// This allows us to map multiple symbols to the same function.
 functions: std.AutoArrayHashMapUnmanaged(
     struct { file: File.Index, index: u32 },
     struct { func: std.wasm.Func, sym_index: u32 },
 ) = .{},
 /// Output global section
 wasm_globals: std.ArrayListUnmanaged(std.wasm.Global) = .{},
 /// Memory section
 memories: std.wasm.Memory = .{ .limits = .{
     .min = 0,
     .max = undefined,
     .flags = 0,
 } },
 /// Output table section
 tables: std.ArrayListUnmanaged(std.wasm.Table) = .{},
 /// Output export section
 exports: std.ArrayListUnmanaged(types.Export) = .{},
 /// List of initialization functions. These must be called in order of priority
 /// by the (synthetic) __wasm_call_ctors function.
 init_funcs: std.ArrayListUnmanaged(InitFuncLoc) = .{},
 /// Index to a function defining the entry of the wasm file
 entry: ?u32 = null,
 
 /// Indirect function table, used to call function pointers
 /// When this is non-zero, we must emit a table entry,
 /// as well as an 'elements' section.
 ///
 /// Note: Key is symbol location, value represents the index into the table
 function_table: std.AutoHashMapUnmanaged(SymbolLoc, u32) = .{},
 
 /// All object files and their data which are linked into the final binary
 objects: std.ArrayListUnmanaged(File.Index) = .{},
 /// All archive files that are lazy loaded.
 /// e.g. when an undefined symbol references a symbol from the archive.
 archives: std.ArrayListUnmanaged(Archive) = .{},
 
 /// A map of global names (read: offset into string table) to their symbol location
 globals: std.AutoHashMapUnmanaged(u32, SymbolLoc) = .{},
 /// The list of GOT symbols and their location
 got_symbols: std.ArrayListUnmanaged(SymbolLoc) = .{},
 /// Maps discarded symbols and their positions to the location of the symbol
 /// it was resolved to
 discarded: std.AutoHashMapUnmanaged(SymbolLoc, SymbolLoc) = .{},
 /// List of all symbol locations which have been resolved by the linker and will be emit
 /// into the final binary.
 resolved_symbols: std.AutoArrayHashMapUnmanaged(SymbolLoc, void) = .{},
 /// Symbols that remain undefined after symbol resolution.
 /// Note: The key represents an offset into the string table, rather than the actual string.
 undefs: std.AutoArrayHashMapUnmanaged(u32, SymbolLoc) = .{},
 /// Maps a symbol's location to an atom. This can be used to find meta
 /// data of a symbol, such as its size, or its offset to perform a relocation.
 /// Undefined (and synthetic) symbols do not have an Atom and therefore cannot be mapped.
 symbol_atom: std.AutoHashMapUnmanaged(SymbolLoc, Atom.Index) = .{},
 /// Maps a symbol's location to its export name, which may differ from the decl's name
 /// which does the exporting.
 /// Note: The value represents the offset into the string table, rather than the actual string.
 export_names: std.AutoHashMapUnmanaged(SymbolLoc, u32) = .{},
 
 /// List of atom indexes of functions that are generated by the backend,
 /// rather than by the linker.
 synthetic_functions: std.ArrayListUnmanaged(Atom.Index) = .{},
 
 pub const Alignment = types.Alignment;
 
 pub const Segment = struct {
     alignment: Alignment,
     size: u32,
     offset: u32,
     flags: u32,
 
     pub const Flag = enum(u32) {
         WASM_DATA_SEGMENT_IS_PASSIVE = 0x01,
         WASM_DATA_SEGMENT_HAS_MEMINDEX = 0x02,
     };
 
     pub fn isPassive(segment: Segment) bool {
         return segment.flags & @intFromEnum(Flag.WASM_DATA_SEGMENT_IS_PASSIVE) != 0;
     }
 
     /// For a given segment, determines if it needs passive initialization
     fn needsPassiveInitialization(segment: Segment, import_mem: bool, name: []const u8) bool {
         if (import_mem and !std.mem.eql(u8, name, ".bss")) {
             return true;
         }
         return segment.isPassive();
     }
 };
 
 pub const Export = struct {
     sym_index: ?u32 = null,
 };
 
 pub const SymbolLoc = struct {
     /// The index of the symbol within the specified file
     index: u32,
     /// The index of the object file where the symbol resides.
     file: File.Index,
 
     /// From a given location, returns the corresponding symbol in the wasm binary
     pub fn getSymbol(loc: SymbolLoc, wasm_file: *const Wasm) *Symbol {
         if (wasm_file.discarded.get(loc)) |new_loc| {
             return new_loc.getSymbol(wasm_file);
         }
         if (wasm_file.file(loc.file)) |obj_file| {
             return obj_file.symbol(loc.index);
         }
         return &wasm_file.synthetic_symbols.items[loc.index];
     }
 
     /// From a given location, returns the name of the symbol.
     pub fn getName(loc: SymbolLoc, wasm_file: *const Wasm) []const u8 {
         if (wasm_file.discarded.get(loc)) |new_loc| {
             return new_loc.getName(wasm_file);
         }
         if (wasm_file.file(loc.file)) |obj_file| {
             return obj_file.symbolName(loc.index);
         }
         return wasm_file.string_table.get(wasm_file.synthetic_symbols.items[loc.index].name);
     }
 
     /// From a given symbol location, returns the final location.
     /// e.g. when a symbol was resolved and replaced by the symbol
     /// in a different file, this will return said location.
     /// If the symbol wasn't replaced by another, this will return
     /// the given location itwasm.
     pub fn finalLoc(loc: SymbolLoc, wasm_file: *const Wasm) SymbolLoc {
         if (wasm_file.discarded.get(loc)) |new_loc| {
             return new_loc.finalLoc(wasm_file);
         }
         return loc;
     }
 };
 
 // Contains the location of the function symbol, as well as
 /// the priority itself of the initialization function.
 pub const InitFuncLoc = struct {
     /// object file index in the list of objects.
     /// Unlike `SymbolLoc` this cannot be `null` as we never define
     /// our own ctors.
     file: File.Index,
     /// Symbol index within the corresponding object file.
     index: u32,
     /// The priority in which the constructor must be called.
     priority: u32,
 
     /// From a given `InitFuncLoc` returns the corresponding function symbol
     fn getSymbol(loc: InitFuncLoc, wasm: *const Wasm) *Symbol {
         return getSymbolLoc(loc).getSymbol(wasm);
     }
 
     /// Turns the given `InitFuncLoc` into a `SymbolLoc`
     fn getSymbolLoc(loc: InitFuncLoc) SymbolLoc {
         return .{ .file = loc.file, .index = loc.index };
     }
 
     /// Returns true when `lhs` has a higher priority (e.i. value closer to 0) than `rhs`.
     fn lessThan(ctx: void, lhs: InitFuncLoc, rhs: InitFuncLoc) bool {
         _ = ctx;
         return lhs.priority < rhs.priority;
     }
 };
 /// Generic string table that duplicates strings
 /// and converts them into offsets instead.
 pub const StringTable = struct {
     /// Table that maps string offsets, which is used to de-duplicate strings.
     /// Rather than having the offset map to the data, the `StringContext` holds all bytes of the string.
     /// The strings are stored as a contigious array where each string is zero-terminated.
     string_table: std.HashMapUnmanaged(
         u32,
         void,
         std.hash_map.StringIndexContext,
         std.hash_map.default_max_load_percentage,
     ) = .{},
     /// Holds the actual data of the string table.
     string_data: std.ArrayListUnmanaged(u8) = .{},
 
     /// Accepts a string and searches for a corresponding string.
     /// When found, de-duplicates the string and returns the existing offset instead.
     /// When the string is not found in the `string_table`, a new entry will be inserted
     /// and the new offset to its data will be returned.
     pub fn put(table: *StringTable, allocator: Allocator, string: []const u8) !u32 {
         const gop = try table.string_table.getOrPutContextAdapted(
             allocator,
             string,
             std.hash_map.StringIndexAdapter{ .bytes = &table.string_data },
             .{ .bytes = &table.string_data },
         );
         if (gop.found_existing) {
             const off = gop.key_ptr.*;
             log.debug("reusing string '{s}' at offset 0x{x}", .{ string, off });
             return off;
         }
 
         try table.string_data.ensureUnusedCapacity(allocator, string.len + 1);
         const offset = @as(u32, @intCast(table.string_data.items.len));
 
         log.debug("writing new string '{s}' at offset 0x{x}", .{ string, offset });
 
         table.string_data.appendSliceAssumeCapacity(string);
         table.string_data.appendAssumeCapacity(0);
 
         gop.key_ptr.* = offset;
 
         return offset;
     }
 
     /// From a given offset, returns its corresponding string value.
     /// Asserts offset does not exceed bounds.
     pub fn get(table: StringTable, off: u32) []const u8 {
         assert(off < table.string_data.items.len);
         return mem.sliceTo(@as([*:0]const u8, @ptrCast(table.string_data.items.ptr + off)), 0);
     }
 
     /// Returns the offset of a given string when it exists.
     /// Will return null if the given string does not yet exist within the string table.
     pub fn getOffset(table: *StringTable, string: []const u8) ?u32 {
         return table.string_table.getKeyAdapted(
             string,
             std.hash_map.StringIndexAdapter{ .bytes = &table.string_data },
         );
     }
 
     /// Frees all resources of the string table. Any references pointing
     /// to the strings will be invalid.
     pub fn deinit(table: *StringTable, allocator: Allocator) void {
         table.string_data.deinit(allocator);
         table.string_table.deinit(allocator);
         table.* = undefined;
     }
 };
 
 pub fn open(
     arena: Allocator,
     comp: *Compilation,
     emit: Compilation.Emit,
     options: link.File.OpenOptions,
 ) !*Wasm {
     // TODO: restore saved linker state, don't truncate the file, and
     // participate in incremental compilation.
     return createEmpty(arena, comp, emit, options);
 }
 
 pub fn createEmpty(
     arena: Allocator,
     comp: *Compilation,
     emit: Compilation.Emit,
     options: link.File.OpenOptions,
 ) !*Wasm {
     const gpa = comp.gpa;
     const target = comp.root_mod.resolved_target.result;
     assert(target.ofmt == .wasm);
 
     const use_lld = build_options.have_llvm and comp.config.use_lld;
     const use_llvm = comp.config.use_llvm;
     const output_mode = comp.config.output_mode;
     const shared_memory = comp.config.shared_memory;
     const wasi_exec_model = comp.config.wasi_exec_model;
 
     // If using LLD to link, this code should produce an object file so that it
     // can be passed to LLD.
     // If using LLVM to generate the object file for the zig compilation unit,
     // we need a place to put the object file so that it can be subsequently
     // handled.
     const zcu_object_sub_path = if (!use_lld and !use_llvm)
         null
     else
         try std.fmt.allocPrint(arena, "{s}.o", .{emit.sub_path});
 
     const wasm = try arena.create(Wasm);
     wasm.* = .{
         .base = .{
             .tag = .wasm,
             .comp = comp,
             .emit = emit,
             .zcu_object_sub_path = zcu_object_sub_path,
             .gc_sections = options.gc_sections orelse (output_mode != .Obj),
             .print_gc_sections = options.print_gc_sections,
             .stack_size = options.stack_size orelse switch (target.os.tag) {
                 .freestanding => 1 * 1024 * 1024, // 1 MiB
                 else => 16 * 1024 * 1024, // 16 MiB
             },
             .allow_shlib_undefined = options.allow_shlib_undefined orelse false,
             .file = null,
             .disable_lld_caching = options.disable_lld_caching,
             .build_id = options.build_id,
             .rpath_list = options.rpath_list,
         },
         .name = undefined,
         .import_table = options.import_table,
         .export_table = options.export_table,
         .import_symbols = options.import_symbols,
         .export_symbol_names = options.export_symbol_names,
         .global_base = options.global_base,
         .initial_memory = options.initial_memory,
         .max_memory = options.max_memory,
 
         .entry_name = switch (options.entry) {
             .disabled => null,
             .default => if (output_mode != .Exe) null else defaultEntrySymbolName(wasi_exec_model),
             .enabled => defaultEntrySymbolName(wasi_exec_model),
             .named => |name| name,
         },
     };
     if (use_llvm and comp.config.have_zcu) {
         wasm.llvm_object = try LlvmObject.create(arena, comp);
     }
     errdefer wasm.base.destroy();
 
     if (use_lld and (use_llvm or !comp.config.have_zcu)) {
         // LLVM emits the object file (if any); LLD links it into the final product.
         return wasm;
     }
 
     // What path should this Wasm linker code output to?
     // If using LLD to link, this code should produce an object file so that it
     // can be passed to LLD.
     const sub_path = if (use_lld) zcu_object_sub_path.? else emit.sub_path;
 
     wasm.base.file = try emit.directory.handle.createFile(sub_path, .{
         .truncate = true,
         .read = true,
         .mode = if (fs.has_executable_bit)
             if (target.os.tag == .wasi and output_mode == .Exe)
                 fs.File.default_mode | 0b001_000_000
             else
                 fs.File.default_mode
         else
             0,
     });
     wasm.name = sub_path;
 
     // create stack pointer symbol
     {
         const loc = try wasm.createSyntheticSymbol("__stack_pointer", .global);
         const symbol = loc.getSymbol(wasm);
         // For object files we will import the stack pointer symbol
         if (output_mode == .Obj) {
             symbol.setUndefined(true);
             symbol.index = @intCast(wasm.imported_globals_count);
             wasm.imported_globals_count += 1;
             try wasm.imports.putNoClobber(
                 gpa,
                 loc,
                 .{
                     .module_name = try wasm.string_table.put(gpa, wasm.host_name),
                     .name = symbol.name,
                     .kind = .{ .global = .{ .valtype = .i32, .mutable = true } },
                 },
             );
         } else {
             symbol.index = @intCast(wasm.imported_globals_count + wasm.wasm_globals.items.len);
             symbol.setFlag(.WASM_SYM_VISIBILITY_HIDDEN);
             const global = try wasm.wasm_globals.addOne(gpa);
             global.* = .{
                 .global_type = .{
                     .valtype = .i32,
                     .mutable = true,
                 },
                 .init = .{ .i32_const = 0 },
             };
         }
     }
 
     // create indirect function pointer symbol
     {
         const loc = try wasm.createSyntheticSymbol("__indirect_function_table", .table);
         const symbol = loc.getSymbol(wasm);
         const table: std.wasm.Table = .{
             .limits = .{ .flags = 0, .min = 0, .max = undefined }, // will be overwritten during `mapFunctionTable`
             .reftype = .funcref,
         };
         if (output_mode == .Obj or options.import_table) {
             symbol.setUndefined(true);
             symbol.index = @intCast(wasm.imported_tables_count);
             wasm.imported_tables_count += 1;
             try wasm.imports.put(gpa, loc, .{
                 .module_name = try wasm.string_table.put(gpa, wasm.host_name),
                 .name = symbol.name,
                 .kind = .{ .table = table },
             });
         } else {
             symbol.index = @as(u32, @intCast(wasm.imported_tables_count + wasm.tables.items.len));
             try wasm.tables.append(gpa, table);
             if (wasm.export_table) {
                 symbol.setFlag(.WASM_SYM_EXPORTED);
             } else {
                 symbol.setFlag(.WASM_SYM_VISIBILITY_HIDDEN);
             }
         }
     }
 
     // create __wasm_call_ctors
     {
         const loc = try wasm.createSyntheticSymbol("__wasm_call_ctors", .function);
         const symbol = loc.getSymbol(wasm);
         symbol.setFlag(.WASM_SYM_VISIBILITY_HIDDEN);
         // we do not know the function index until after we merged all sections.
         // Therefore we set `symbol.index` and create its corresponding references
         // at the end during `initializeCallCtorsFunction`.
     }
 
     // shared-memory symbols for TLS support
     if (shared_memory) {
         {
             const loc = try wasm.createSyntheticSymbol("__tls_base", .global);
             const symbol = loc.getSymbol(wasm);
             symbol.setFlag(.WASM_SYM_VISIBILITY_HIDDEN);
             symbol.index = @intCast(wasm.imported_globals_count + wasm.wasm_globals.items.len);
             try wasm.wasm_globals.append(gpa, .{
                 .global_type = .{ .valtype = .i32, .mutable = true },
                 .init = .{ .i32_const = undefined },
             });
         }
         {
             const loc = try wasm.createSyntheticSymbol("__tls_size", .global);
             const symbol = loc.getSymbol(wasm);
             symbol.setFlag(.WASM_SYM_VISIBILITY_HIDDEN);
             symbol.index = @intCast(wasm.imported_globals_count + wasm.wasm_globals.items.len);
             try wasm.wasm_globals.append(gpa, .{
                 .global_type = .{ .valtype = .i32, .mutable = false },
                 .init = .{ .i32_const = undefined },
             });
         }
         {
             const loc = try wasm.createSyntheticSymbol("__tls_align", .global);
             const symbol = loc.getSymbol(wasm);
             symbol.setFlag(.WASM_SYM_VISIBILITY_HIDDEN);
             symbol.index = @intCast(wasm.imported_globals_count + wasm.wasm_globals.items.len);
             try wasm.wasm_globals.append(gpa, .{
                 .global_type = .{ .valtype = .i32, .mutable = false },
                 .init = .{ .i32_const = undefined },
             });
         }
         {
             const loc = try wasm.createSyntheticSymbol("__wasm_init_tls", .function);
             const symbol = loc.getSymbol(wasm);
             symbol.setFlag(.WASM_SYM_VISIBILITY_HIDDEN);
         }
     }
 
     if (comp.module) |zcu| {
         if (!use_llvm) {
             const index: File.Index = @enumFromInt(wasm.files.len);
             var zig_object: ZigObject = .{
                 .index = index,
                 .path = try std.fmt.allocPrint(gpa, "{s}.o", .{std.fs.path.stem(zcu.main_mod.root_src_path)}),
                 .stack_pointer_sym = undefined,
             };
             try zig_object.init(wasm);
             try wasm.files.append(gpa, .{ .zig_object = zig_object });
             wasm.zig_object_index = index;
         }
     }
 
     return wasm;
 }
 
 pub fn file(wasm: *const Wasm, index: File.Index) ?File {
     if (index == .null) return null;
     const tag = wasm.files.items(.tags)[@intFromEnum(index)];
     return switch (tag) {
         .zig_object => .{ .zig_object = &wasm.files.items(.data)[@intFromEnum(index)].zig_object },
         .object => .{ .object = &wasm.files.items(.data)[@intFromEnum(index)].object },
     };
 }
 
 pub fn zigObjectPtr(wasm: *Wasm) ?*ZigObject {
     if (wasm.zig_object_index == .null) return null;
     return &wasm.files.items(.data)[@intFromEnum(wasm.zig_object_index)].zig_object;
 }
 
 pub fn getTypeIndex(wasm: *const Wasm, func_type: std.wasm.Type) ?u32 {
     var index: u32 = 0;
     while (index < wasm.func_types.items.len) : (index += 1) {
         if (wasm.func_types.items[index].eql(func_type)) return index;
     }
     return null;
 }
 
 /// Either creates a new import, or updates one if existing.
 /// When `type_index` is non-null, we assume an external function.
 /// In all other cases, a data-symbol will be created instead.
 pub fn addOrUpdateImport(
     wasm: *Wasm,
     /// Name of the import
     name: []const u8,
     /// Symbol index that is external
     symbol_index: u32,
     /// Optional library name (i.e. `extern "c" fn foo() void`
     lib_name: ?[:0]const u8,
     /// The index of the type that represents the function signature
     /// when the extern is a function. When this is null, a data-symbol
     /// is asserted instead.
     type_index: ?u32,
 ) !void {
     return wasm.zigObjectPtr().?.addOrUpdateImport(wasm, name, symbol_index, lib_name, type_index);
 }
 
 /// For a given name, creates a new global synthetic symbol.
 /// Leaves index undefined and the default flags (0).
 fn createSyntheticSymbol(wasm: *Wasm, name: []const u8, tag: Symbol.Tag) !SymbolLoc {
     const gpa = wasm.base.comp.gpa;
     const name_offset = try wasm.string_table.put(gpa, name);
     return wasm.createSyntheticSymbolOffset(name_offset, tag);
 }
 
 fn createSyntheticSymbolOffset(wasm: *Wasm, name_offset: u32, tag: Symbol.Tag) !SymbolLoc {
     const sym_index = @as(u32, @intCast(wasm.synthetic_symbols.items.len));
     const loc: SymbolLoc = .{ .index = sym_index, .file = .null };
     const gpa = wasm.base.comp.gpa;
     try wasm.synthetic_symbols.append(gpa, .{
         .name = name_offset,
         .flags = 0,
         .tag = tag,
         .index = undefined,
         .virtual_address = undefined,
     });
     try wasm.resolved_symbols.putNoClobber(gpa, loc, {});
     try wasm.globals.put(gpa, name_offset, loc);
     return loc;
 }
 
 fn parseInputFiles(wasm: *Wasm, files: []const []const u8) !void {
     for (files) |path| {
         if (try wasm.parseObjectFile(path)) continue;
         if (try wasm.parseArchive(path, false)) continue; // load archives lazily
         log.warn("Unexpected file format at path: '{s}'", .{path});
     }
 }
 
 /// Parses the object file from given path. Returns true when the given file was an object
 /// file and parsed successfully. Returns false when file is not an object file.
 /// May return an error instead when parsing failed.
 fn parseObjectFile(wasm: *Wasm, path: []const u8) !bool {
     const obj_file = try fs.cwd().openFile(path, .{});
     errdefer obj_file.close();
 
     const gpa = wasm.base.comp.gpa;
     var object = Object.create(gpa, obj_file, path, null) catch |err| switch (err) {
         error.InvalidMagicByte, error.NotObjectFile => return false,
         else => |e| return e,
     };
     errdefer object.deinit(gpa);
     object.index = @enumFromInt(wasm.files.len);
     try wasm.files.append(gpa, .{ .object = object });
     try wasm.objects.append(gpa, object.index);
     return true;
 }
 
 /// Creates a new empty `Atom` and returns its `Atom.Index`
 pub fn createAtom(wasm: *Wasm, sym_index: u32, file_index: File.Index) !Atom.Index {
     const gpa = wasm.base.comp.gpa;
     const index: Atom.Index = @intCast(wasm.managed_atoms.items.len);
     const atom = try wasm.managed_atoms.addOne(gpa);
     atom.* = .{ .file = file_index, .sym_index = sym_index };
     try wasm.symbol_atom.putNoClobber(gpa, atom.symbolLoc(), index);
 
     return index;
 }
 
 pub inline fn getAtom(wasm: *const Wasm, index: Atom.Index) Atom {
     return wasm.managed_atoms.items[index];
 }
 
 pub inline fn getAtomPtr(wasm: *Wasm, index: Atom.Index) *Atom {
     return &wasm.managed_atoms.items[index];
 }
 
 /// Parses an archive file and will then parse each object file
 /// that was found in the archive file.
 /// Returns false when the file is not an archive file.
 /// May return an error instead when parsing failed.
 ///
 /// When `force_load` is `true`, it will for link all object files in the archive.
 /// When false, it will only link with object files that contain symbols that
 /// are referenced by other object files or Zig code.
 fn parseArchive(wasm: *Wasm, path: []const u8, force_load: bool) !bool {
     const gpa = wasm.base.comp.gpa;
 
     const archive_file = try fs.cwd().openFile(path, .{});
     errdefer archive_file.close();
 
     var archive: Archive = .{
         .file = archive_file,
         .name = path,
     };
     archive.parse(gpa) catch |err| switch (err) {
         error.EndOfStream, error.NotArchive => {
             archive.deinit(gpa);
             return false;
         },
         else => |e| return e,
     };
 
     if (!force_load) {
         errdefer archive.deinit(gpa);
         try wasm.archives.append(gpa, archive);
         return true;
     }
     defer archive.deinit(gpa);
 
     // In this case we must force link all embedded object files within the archive
     // We loop over all symbols, and then group them by offset as the offset
     // notates where the object file starts.
     var offsets = std.AutoArrayHashMap(u32, void).init(gpa);
     defer offsets.deinit();
     for (archive.toc.values()) |symbol_offsets| {
         for (symbol_offsets.items) |sym_offset| {
             try offsets.put(sym_offset, {});
         }
     }
 
     for (offsets.keys()) |file_offset| {
         var object = try archive.parseObject(gpa, file_offset);
         object.index = @enumFromInt(wasm.files.len);
         try wasm.files.append(gpa, .{ .object = object });
         try wasm.objects.append(gpa, object.index);
     }
 
     return true;
 }
 
 fn requiresTLSReloc(wasm: *const Wasm) bool {
     for (wasm.got_symbols.items) |loc| {
         if (loc.getSymbol(wasm).isTLS()) {
             return true;
         }
     }
     return false;
 }
 
 fn resolveSymbolsInObject(wasm: *Wasm, file_index: File.Index) !void {
     const gpa = wasm.base.comp.gpa;
     const obj_file = wasm.file(file_index).?;
     log.debug("Resolving symbols in object: '{s}'", .{obj_file.path()});
 
     for (obj_file.symbols(), 0..) |symbol, i| {
         const sym_index: u32 = @intCast(i);
         const location: SymbolLoc = .{ .file = file_index, .index = sym_index };
         const sym_name = obj_file.string(symbol.name);
         if (mem.eql(u8, sym_name, "__indirect_function_table")) {
             continue;
         }
         const sym_name_index = try wasm.string_table.put(gpa, sym_name);
 
         if (symbol.isLocal()) {
             if (symbol.isUndefined()) {
                 log.err("Local symbols are not allowed to reference imports", .{});
                 log.err("  symbol '{s}' defined in '{s}'", .{ sym_name, obj_file.path() });
                 return error.UndefinedLocal;
             }
             try wasm.resolved_symbols.putNoClobber(gpa, location, {});
             continue;
         }
 
         const maybe_existing = try wasm.globals.getOrPut(gpa, sym_name_index);
         if (!maybe_existing.found_existing) {
             maybe_existing.value_ptr.* = location;
             try wasm.resolved_symbols.putNoClobber(gpa, location, {});
 
             if (symbol.isUndefined()) {
                 try wasm.undefs.putNoClobber(gpa, sym_name_index, location);
             }
             continue;
         }
 
         const existing_loc = maybe_existing.value_ptr.*;
         const existing_sym: *Symbol = existing_loc.getSymbol(wasm);
         const existing_file = wasm.file(existing_loc.file);
 
         const existing_file_path = if (existing_file) |existing_obj_file|
             existing_obj_file.path()
         else
             wasm.name;
 
         if (!existing_sym.isUndefined()) outer: {
             if (!symbol.isUndefined()) inner: {
                 if (symbol.isWeak()) {
                     break :inner; // ignore the new symbol (discard it)
                 }
                 if (existing_sym.isWeak()) {
                     break :outer; // existing is weak, while new one isn't. Replace it.
                 }
                 // both are defined and weak, we have a symbol collision.
                 log.err("symbol '{s}' defined multiple times", .{sym_name});
                 log.err("  first definition in '{s}'", .{existing_file_path});
                 log.err("  next definition in '{s}'", .{obj_file.path()});
                 return error.SymbolCollision;
             }
 
             try wasm.discarded.put(gpa, location, existing_loc);
             continue; // Do not overwrite defined symbols with undefined symbols
         }
 
         if (symbol.tag != existing_sym.tag) {
             log.err("symbol '{s}' mismatching types '{s}' and '{s}'", .{ sym_name, @tagName(symbol.tag), @tagName(existing_sym.tag) });
             log.err("  first definition in '{s}'", .{existing_file_path});
             log.err("  next definition in '{s}'", .{obj_file.path()});
             return error.SymbolMismatchingType;
         }
 
         if (existing_sym.isUndefined() and symbol.isUndefined()) {
             // only verify module/import name for function symbols
             if (symbol.tag == .function) {
                 const existing_name = if (existing_file) |existing_obj| blk: {
                     const imp = existing_obj.import(existing_loc.index);
                     break :blk existing_obj.string(imp.module_name);
                 } else blk: {
                     const name_index = wasm.imports.get(existing_loc).?.module_name;
                     break :blk wasm.string_table.get(name_index);
                 };
 
                 const imp = obj_file.import(sym_index);
                 const module_name = obj_file.string(imp.module_name);
                 if (!mem.eql(u8, existing_name, module_name)) {
                     log.err("symbol '{s}' module name mismatch. Expected '{s}', but found '{s}'", .{
                         sym_name,
                         existing_name,
                         module_name,
                     });
                     log.err("  first definition in '{s}'", .{existing_file_path});
                     log.err("  next definition in '{s}'", .{obj_file.path()});
                     return error.ModuleNameMismatch;
                 }
             }
 
             // both undefined so skip overwriting existing symbol and discard the new symbol
             try wasm.discarded.put(gpa, location, existing_loc);
             continue;
         }
 
         if (existing_sym.tag == .global) {
             const existing_ty = wasm.getGlobalType(existing_loc);
             const new_ty = wasm.getGlobalType(location);
             if (existing_ty.mutable != new_ty.mutable or existing_ty.valtype != new_ty.valtype) {
                 log.err("symbol '{s}' mismatching global types", .{sym_name});
                 log.err("  first definition in '{s}'", .{existing_file_path});
                 log.err("  next definition in '{s}'", .{obj_file.path()});
                 return error.GlobalTypeMismatch;
             }
         }
 
         if (existing_sym.tag == .function) {
             const existing_ty = wasm.getFunctionSignature(existing_loc);
             const new_ty = wasm.getFunctionSignature(location);
             if (!existing_ty.eql(new_ty)) {
                 log.err("symbol '{s}' mismatching function signatures.", .{sym_name});
                 log.err("  expected signature {}, but found signature {}", .{ existing_ty, new_ty });
                 log.err("  first definition in '{s}'", .{existing_file_path});
                 log.err("  next definition in '{s}'", .{obj_file.path()});
                 return error.FunctionSignatureMismatch;
             }
         }
 
         // when both symbols are weak, we skip overwriting unless the existing
         // symbol is weak and the new one isn't, in which case we *do* overwrite it.
         if (existing_sym.isWeak() and symbol.isWeak()) blk: {
             if (existing_sym.isUndefined() and !symbol.isUndefined()) break :blk;
             try wasm.discarded.put(gpa, location, existing_loc);
             continue;
         }
 
         // simply overwrite with the new symbol
         log.debug("Overwriting symbol '{s}'", .{sym_name});
         log.debug("  old definition in '{s}'", .{existing_file_path});
         log.debug("  new definition in '{s}'", .{obj_file.path()});
         try wasm.discarded.putNoClobber(gpa, existing_loc, location);
         maybe_existing.value_ptr.* = location;
         try wasm.globals.put(gpa, sym_name_index, location);
         try wasm.resolved_symbols.put(gpa, location, {});
         assert(wasm.resolved_symbols.swapRemove(existing_loc));
         if (existing_sym.isUndefined()) {
             _ = wasm.undefs.swapRemove(sym_name_index);
         }
     }
 }
 
 fn resolveSymbolsInArchives(wasm: *Wasm) !void {
     const gpa = wasm.base.comp.gpa;
     if (wasm.archives.items.len == 0) return;
 
     log.debug("Resolving symbols in archives", .{});
     var index: u32 = 0;
     undef_loop: while (index < wasm.undefs.count()) {
         const sym_name_index = wasm.undefs.keys()[index];
 
         for (wasm.archives.items) |archive| {
             const sym_name = wasm.string_table.get(sym_name_index);
             log.debug("Detected symbol '{s}' in archive '{s}', parsing objects..", .{ sym_name, archive.name });
             const offset = archive.toc.get(sym_name) orelse {
                 // symbol does not exist in this archive
                 continue;
             };
 
             // Symbol is found in unparsed object file within current archive.
             // Parse object and and resolve symbols again before we check remaining
             // undefined symbols.
             var object = try archive.parseObject(gpa, offset.items[0]);
             object.index = @enumFromInt(wasm.files.len);
             try wasm.files.append(gpa, .{ .object = object });
             try wasm.objects.append(gpa, object.index);
             try wasm.resolveSymbolsInObject(object.index);
 
             // continue loop for any remaining undefined symbols that still exist
             // after resolving last object file
             continue :undef_loop;
         }
         index += 1;
     }
 }
 
 /// Writes an unsigned 32-bit integer as a LEB128-encoded 'i32.const' value.
 fn writeI32Const(writer: anytype, val: u32) !void {
     try writer.writeByte(std.wasm.opcode(.i32_const));
     try leb.writeILEB128(writer, @as(i32, @bitCast(val)));
 }
 
 fn setupInitMemoryFunction(wasm: *Wasm) !void {
     const comp = wasm.base.comp;
     const gpa = comp.gpa;
     const shared_memory = comp.config.shared_memory;
     const import_memory = comp.config.import_memory;
 
     // Passive segments are used to avoid memory being reinitialized on each
     // thread's instantiation. These passive segments are initialized and
     // dropped in __wasm_init_memory, which is registered as the start function
     // We also initialize bss segments (using memory.fill) as part of this
     // function.
     if (!wasm.hasPassiveInitializationSegments()) {
         return;
     }
 
     const flag_address: u32 = if (shared_memory) address: {
         // when we have passive initialization segments and shared memory
         // `setupMemory` will create this symbol and set its virtual address.
         const loc = wasm.findGlobalSymbol("__wasm_init_memory_flag").?;
         break :address loc.getSymbol(wasm).virtual_address;
     } else 0;
 
     var function_body = std.ArrayList(u8).init(gpa);
     defer function_body.deinit();
     const writer = function_body.writer();
 
     // we have 0 locals
     try leb.writeULEB128(writer, @as(u32, 0));
 
     if (shared_memory) {
         // destination blocks
         // based on values we jump to corresponding label
         try writer.writeByte(std.wasm.opcode(.block)); // $drop
         try writer.writeByte(std.wasm.block_empty); // block type
 
         try writer.writeByte(std.wasm.opcode(.block)); // $wait
         try writer.writeByte(std.wasm.block_empty); // block type
 
         try writer.writeByte(std.wasm.opcode(.block)); // $init
         try writer.writeByte(std.wasm.block_empty); // block type
 
         // atomically check
         try writeI32Const(writer, flag_address);
         try writeI32Const(writer, 0);
         try writeI32Const(writer, 1);
         try writer.writeByte(std.wasm.opcode(.atomics_prefix));
         try leb.writeULEB128(writer, std.wasm.atomicsOpcode(.i32_atomic_rmw_cmpxchg));
         try leb.writeULEB128(writer, @as(u32, 2)); // alignment
         try leb.writeULEB128(writer, @as(u32, 0)); // offset
 
         // based on the value from the atomic check, jump to the label.
         try writer.writeByte(std.wasm.opcode(.br_table));
         try leb.writeULEB128(writer, @as(u32, 2)); // length of the table (we have 3 blocks but because of the mandatory default the length is 2).
         try leb.writeULEB128(writer, @as(u32, 0)); // $init
         try leb.writeULEB128(writer, @as(u32, 1)); // $wait
         try leb.writeULEB128(writer, @as(u32, 2)); // $drop
         try writer.writeByte(std.wasm.opcode(.end));
     }
 
     var it = wasm.data_segments.iterator();
     var segment_index: u32 = 0;
     while (it.next()) |entry| : (segment_index += 1) {
         const segment: Segment = wasm.segments.items[entry.value_ptr.*];
         if (segment.needsPassiveInitialization(import_memory, entry.key_ptr.*)) {
             // For passive BSS segments we can simple issue a memory.fill(0).
             // For non-BSS segments we do a memory.init.  Both these
             // instructions take as their first argument the destination
             // address.
             try writeI32Const(writer, segment.offset);
 
             if (shared_memory and std.mem.eql(u8, entry.key_ptr.*, ".tdata")) {
                 // When we initialize the TLS segment we also set the `__tls_base`
                 // global.  This allows the runtime to use this static copy of the
                 // TLS data for the first/main thread.
                 try writeI32Const(writer, segment.offset);
                 try writer.writeByte(std.wasm.opcode(.global_set));
                 const loc = wasm.findGlobalSymbol("__tls_base").?;
                 try leb.writeULEB128(writer, loc.getSymbol(wasm).index);
             }
 
             try writeI32Const(writer, 0);
             try writeI32Const(writer, segment.size);
             try writer.writeByte(std.wasm.opcode(.misc_prefix));
             if (std.mem.eql(u8, entry.key_ptr.*, ".bss")) {
                 // fill bss segment with zeroes
                 try leb.writeULEB128(writer, std.wasm.miscOpcode(.memory_fill));
             } else {
                 // initialize the segment
                 try leb.writeULEB128(writer, std.wasm.miscOpcode(.memory_init));
                 try leb.writeULEB128(writer, segment_index);
             }
             try writer.writeByte(0); // memory index immediate
         }
     }
 
     if (shared_memory) {
         // we set the init memory flag to value '2'
         try writeI32Const(writer, flag_address);
         try writeI32Const(writer, 2);
         try writer.writeByte(std.wasm.opcode(.atomics_prefix));
         try leb.writeULEB128(writer, std.wasm.atomicsOpcode(.i32_atomic_store));
         try leb.writeULEB128(writer, @as(u32, 2)); // alignment
         try leb.writeULEB128(writer, @as(u32, 0)); // offset
 
         // notify any waiters for segment initialization completion
         try writeI32Const(writer, flag_address);
         try writer.writeByte(std.wasm.opcode(.i32_const));
         try leb.writeILEB128(writer, @as(i32, -1)); // number of waiters
         try writer.writeByte(std.wasm.opcode(.atomics_prefix));
         try leb.writeULEB128(writer, std.wasm.atomicsOpcode(.memory_atomic_notify));
         try leb.writeULEB128(writer, @as(u32, 2)); // alignment
         try leb.writeULEB128(writer, @as(u32, 0)); // offset
         try writer.writeByte(std.wasm.opcode(.drop));
 
         // branch and drop segments
         try writer.writeByte(std.wasm.opcode(.br));
         try leb.writeULEB128(writer, @as(u32, 1));
 
         // wait for thread to initialize memory segments
         try writer.writeByte(std.wasm.opcode(.end)); // end $wait
         try writeI32Const(writer, flag_address);
         try writeI32Const(writer, 1); // expected flag value
         try writer.writeByte(std.wasm.opcode(.i64_const));
         try leb.writeILEB128(writer, @as(i64, -1)); // timeout
         try writer.writeByte(std.wasm.opcode(.atomics_prefix));
         try leb.writeULEB128(writer, std.wasm.atomicsOpcode(.memory_atomic_wait32));
         try leb.writeULEB128(writer, @as(u32, 2)); // alignment
         try leb.writeULEB128(writer, @as(u32, 0)); // offset
         try writer.writeByte(std.wasm.opcode(.drop));
 
         try writer.writeByte(std.wasm.opcode(.end)); // end $drop
     }
 
     it.reset();
     segment_index = 0;
     while (it.next()) |entry| : (segment_index += 1) {
         const name = entry.key_ptr.*;
         const segment: Segment = wasm.segments.items[entry.value_ptr.*];
         if (segment.needsPassiveInitialization(import_memory, name) and
             !std.mem.eql(u8, name, ".bss"))
         {
             // The TLS region should not be dropped since its is needed
             // during the initialization of each thread (__wasm_init_tls).
             if (shared_memory and std.mem.eql(u8, name, ".tdata")) {
                 continue;
             }
 
             try writer.writeByte(std.wasm.opcode(.misc_prefix));
             try leb.writeULEB128(writer, std.wasm.miscOpcode(.data_drop));
             try leb.writeULEB128(writer, segment_index);
         }
     }
 
     // End of the function body
     try writer.writeByte(std.wasm.opcode(.end));
 
     try wasm.createSyntheticFunction(
         "__wasm_init_memory",
         std.wasm.Type{ .params = &.{}, .returns = &.{} },
         &function_body,
     );
 }
 
 /// Constructs a synthetic function that performs runtime relocations for
 /// TLS symbols. This function is called by `__wasm_init_tls`.
 fn setupTLSRelocationsFunction(wasm: *Wasm) !void {
     const comp = wasm.base.comp;
     const gpa = comp.gpa;
     const shared_memory = comp.config.shared_memory;
 
     // When we have TLS GOT entries and shared memory is enabled,
     // we must perform runtime relocations or else we don't create the function.
     if (!shared_memory or !wasm.requiresTLSReloc()) {
         return;
     }
 
     // const loc = try wasm.createSyntheticSymbol("__wasm_apply_global_tls_relocs");
     var function_body = std.ArrayList(u8).init(gpa);
     defer function_body.deinit();
     const writer = function_body.writer();
 
     // locals (we have none)
     try writer.writeByte(0);
     for (wasm.got_symbols.items, 0..) |got_loc, got_index| {
         const sym: *Symbol = got_loc.getSymbol(wasm);
         if (!sym.isTLS()) continue; // only relocate TLS symbols
         if (sym.tag == .data and sym.isDefined()) {
             // get __tls_base
             try writer.writeByte(std.wasm.opcode(.global_get));
             try leb.writeULEB128(writer, wasm.findGlobalSymbol("__tls_base").?.getSymbol(wasm).index);
 
             // add the virtual address of the symbol
             try writer.writeByte(std.wasm.opcode(.i32_const));
             try leb.writeULEB128(writer, sym.virtual_address);
         } else if (sym.tag == .function) {
             @panic("TODO: relocate GOT entry of function");
         } else continue;
 
         try writer.writeByte(std.wasm.opcode(.i32_add));
         try writer.writeByte(std.wasm.opcode(.global_set));
         try leb.writeULEB128(writer, wasm.imported_globals_count + @as(u32, @intCast(wasm.wasm_globals.items.len + got_index)));
     }
     try writer.writeByte(std.wasm.opcode(.end));
 
     try wasm.createSyntheticFunction(
         "__wasm_apply_global_tls_relocs",
         std.wasm.Type{ .params = &.{}, .returns = &.{} },
         &function_body,
     );
 }
 
 fn validateFeatures(
     wasm: *const Wasm,
     to_emit: *[@typeInfo(types.Feature.Tag).Enum.fields.len]bool,
     emit_features_count: *u32,
 ) !void {
     const comp = wasm.base.comp;
     const target = comp.root_mod.resolved_target.result;
     const shared_memory = comp.config.shared_memory;
     const cpu_features = target.cpu.features;
     const infer = cpu_features.isEmpty(); // when the user did not define any features, we infer them from linked objects.
     const known_features_count = @typeInfo(types.Feature.Tag).Enum.fields.len;
 
     var allowed = [_]bool{false} ** known_features_count;
     var used = [_]u17{0} ** known_features_count;
     var disallowed = [_]u17{0} ** known_features_count;
     var required = [_]u17{0} ** known_features_count;
 
     // when false, we fail linking. We only verify this after a loop to catch all invalid features.
     var valid_feature_set = true;
     // will be set to true when there's any TLS segment found in any of the object files
     var has_tls = false;
 
     // When the user has given an explicit list of features to enable,
     // we extract them and insert each into the 'allowed' list.
     if (!infer) {
         inline for (@typeInfo(std.Target.wasm.Feature).Enum.fields) |feature_field| {
             if (cpu_features.isEnabled(feature_field.value)) {
                 allowed[feature_field.value] = true;
                 emit_features_count.* += 1;
             }
         }
     }
 
     // extract all the used, disallowed and required features from each
     // linked object file so we can test them.
     for (wasm.objects.items) |file_index| {
         const object: Object = wasm.files.items(.data)[@intFromEnum(file_index)].object;
         for (object.features) |feature| {
             const value = @as(u16, @intFromEnum(file_index)) << 1 | @as(u1, 1);
             switch (feature.prefix) {
                 .used => {
                     used[@intFromEnum(feature.tag)] = value;
                 },
                 .disallowed => {
                     disallowed[@intFromEnum(feature.tag)] = value;
                 },
                 .required => {
                     required[@intFromEnum(feature.tag)] = value;
                     used[@intFromEnum(feature.tag)] = value;
                 },
             }
         }
 
         for (object.segment_info) |segment| {
             if (segment.isTLS()) {
                 has_tls = true;
             }
         }
     }
 
     // when we infer the features, we allow each feature found in the 'used' set
     // and insert it into the 'allowed' set. When features are not inferred,
     // we validate that a used feature is allowed.
     for (used, 0..) |used_set, used_index| {
         const is_enabled = @as(u1, @truncate(used_set)) != 0;
         if (infer) {
             allowed[used_index] = is_enabled;
             emit_features_count.* += @intFromBool(is_enabled);
         } else if (is_enabled and !allowed[used_index]) {
             log.err("feature '{}' not allowed, but used by linked object", .{@as(types.Feature.Tag, @enumFromInt(used_index))});
             log.err("  defined in '{s}'", .{wasm.files.items(.data)[used_set >> 1].object.path});
             valid_feature_set = false;
         }
     }
 
     if (!valid_feature_set) {
         return error.InvalidFeatureSet;
     }
 
     if (shared_memory) {
         const disallowed_feature = disallowed[@intFromEnum(types.Feature.Tag.shared_mem)];
         if (@as(u1, @truncate(disallowed_feature)) != 0) {
             log.err(
                 "shared-memory is disallowed by '{s}' because it wasn't compiled with 'atomics' and 'bulk-memory' features enabled",
                 .{wasm.files.items(.data)[disallowed_feature >> 1].object.path},
             );
             valid_feature_set = false;
         }
 
         for ([_]types.Feature.Tag{ .atomics, .bulk_memory }) |feature| {
             if (!allowed[@intFromEnum(feature)]) {
                 log.err("feature '{}' is not used but is required for shared-memory", .{feature});
             }
         }
     }
 
     if (has_tls) {
         for ([_]types.Feature.Tag{ .atomics, .bulk_memory }) |feature| {
             if (!allowed[@intFromEnum(feature)]) {
                 log.err("feature '{}' is not used but is required for thread-local storage", .{feature});
             }
         }
     }
     // For each linked object, validate the required and disallowed features
     for (wasm.objects.items) |file_index| {
         var object_used_features = [_]bool{false} ** known_features_count;
         const object = wasm.files.items(.data)[@intFromEnum(file_index)].object;
         for (object.features) |feature| {
             if (feature.prefix == .disallowed) continue; // already defined in 'disallowed' set.
             // from here a feature is always used
             const disallowed_feature = disallowed[@intFromEnum(feature.tag)];
             if (@as(u1, @truncate(disallowed_feature)) != 0) {
                 log.err("feature '{}' is disallowed, but used by linked object", .{feature.tag});
                 log.err("  disallowed by '{s}'", .{wasm.files.items(.data)[disallowed_feature >> 1].object.path});
                 log.err("  used in '{s}'", .{object.path});
                 valid_feature_set = false;
             }
 
             object_used_features[@intFromEnum(feature.tag)] = true;
         }
 
         // validate the linked object file has each required feature
         for (required, 0..) |required_feature, feature_index| {
             const is_required = @as(u1, @truncate(required_feature)) != 0;
             if (is_required and !object_used_features[feature_index]) {
                 log.err("feature '{}' is required but not used in linked object", .{@as(types.Feature.Tag, @enumFromInt(feature_index))});
                 log.err("  required by '{s}'", .{wasm.files.items(.data)[required_feature >> 1].object.path});
                 log.err("  missing in '{s}'", .{object.path});
                 valid_feature_set = false;
             }
         }
     }
 
     if (!valid_feature_set) {
         return error.InvalidFeatureSet;
     }
 
     to_emit.* = allowed;
 }
 
 /// Creates synthetic linker-symbols, but only if they are being referenced from
 /// any object file. For instance, the `__heap_base` symbol will only be created,
 /// if one or multiple undefined references exist. When none exist, the symbol will
 /// not be created, ensuring we don't unneccesarily emit unreferenced symbols.
 fn resolveLazySymbols(wasm: *Wasm) !void {
     const comp = wasm.base.comp;
     const gpa = comp.gpa;
     const shared_memory = comp.config.shared_memory;
 
     if (wasm.string_table.getOffset("__heap_base")) |name_offset| {
         if (wasm.undefs.fetchSwapRemove(name_offset)) |kv| {
             const loc = try wasm.createSyntheticSymbolOffset(name_offset, .data);
             try wasm.discarded.putNoClobber(gpa, kv.value, loc);
             _ = wasm.resolved_symbols.swapRemove(loc); // we don't want to emit this symbol, only use it for relocations.
         }
     }
 
     if (wasm.string_table.getOffset("__heap_end")) |name_offset| {
         if (wasm.undefs.fetchSwapRemove(name_offset)) |kv| {
             const loc = try wasm.createSyntheticSymbolOffset(name_offset, .data);
             try wasm.discarded.putNoClobber(gpa, kv.value, loc);
             _ = wasm.resolved_symbols.swapRemove(loc);
         }
     }
 
     if (!shared_memory) {
         if (wasm.string_table.getOffset("__tls_base")) |name_offset| {
             if (wasm.undefs.fetchSwapRemove(name_offset)) |kv| {
                 const loc = try wasm.createSyntheticSymbolOffset(name_offset, .global);
                 try wasm.discarded.putNoClobber(gpa, kv.value, loc);
                 _ = wasm.resolved_symbols.swapRemove(kv.value);
                 const symbol = loc.getSymbol(wasm);
                 symbol.setFlag(.WASM_SYM_VISIBILITY_HIDDEN);
                 symbol.index = @intCast(wasm.imported_globals_count + wasm.wasm_globals.items.len);
                 try wasm.wasm_globals.append(gpa, .{
                     .global_type = .{ .valtype = .i32, .mutable = true },
                     .init = .{ .i32_const = undefined },
                 });
             }
         }
     }
     if (wasm.string_table.getOffset("__zig_errors_len")) |name_offset| {
         if (wasm.undefs.fetchSwapRemove(name_offset)) |kv| {
             const loc = try wasm.createSyntheticSymbolOffset(name_offset, .data);
             try wasm.discarded.putNoClobber(gpa, kv.value, loc);
             _ = wasm.resolved_symbols.swapRemove(kv.value);
         }
     }
 }
 
 // Tries to find a global symbol by its name. Returns null when not found,
 /// and its location when it is found.
 pub fn findGlobalSymbol(wasm: *Wasm, name: []const u8) ?SymbolLoc {
     const offset = wasm.string_table.getOffset(name) orelse return null;
     return wasm.globals.get(offset);
 }
 
 fn checkUndefinedSymbols(wasm: *const Wasm) !void {
     const comp = wasm.base.comp;
     if (comp.config.output_mode == .Obj) return;
     if (wasm.import_symbols) return;
 
     var found_undefined_symbols = false;
     for (wasm.undefs.values()) |undef| {
         const symbol = undef.getSymbol(wasm);
         if (symbol.tag == .data) {
             found_undefined_symbols = true;
             const file_name = if (wasm.file(undef.file)) |obj_file|
                 obj_file.path()
             else
                 wasm.name;
             const symbol_name = undef.getName(wasm);
             log.err("could not resolve undefined symbol '{s}'", .{symbol_name});
             log.err("  defined in '{s}'", .{file_name});
         }
     }
     if (found_undefined_symbols) {
         return error.UndefinedSymbol;
     }
 }
 
 pub fn deinit(wasm: *Wasm) void {
     const gpa = wasm.base.comp.gpa;
     if (wasm.llvm_object) |llvm_object| llvm_object.deinit();
 
     for (wasm.func_types.items) |*func_type| {
         func_type.deinit(gpa);
     }
     for (wasm.segment_info.values()) |segment_info| {
         gpa.free(segment_info.name);
     }
     if (wasm.zigObjectPtr()) |zig_obj| {
         zig_obj.deinit(wasm);
     }
     for (wasm.objects.items) |obj_index| {
         wasm.file(obj_index).?.object.deinit(gpa);
     }
 
     for (wasm.archives.items) |*archive| {
         archive.deinit(gpa);
     }
 
     for (wasm.synthetic_functions.items) |atom_index| {
         const atom = wasm.getAtomPtr(atom_index);
         atom.deinit(gpa);
     }
 
     wasm.synthetic_symbols.deinit(gpa);
     wasm.globals.deinit(gpa);
     wasm.resolved_symbols.deinit(gpa);
     wasm.undefs.deinit(gpa);
     wasm.discarded.deinit(gpa);
     wasm.symbol_atom.deinit(gpa);
     wasm.export_names.deinit(gpa);
     wasm.atoms.deinit(gpa);
     wasm.managed_atoms.deinit(gpa);
     wasm.segments.deinit(gpa);
     wasm.data_segments.deinit(gpa);
     wasm.segment_info.deinit(gpa);
     wasm.objects.deinit(gpa);
     wasm.archives.deinit(gpa);
 
     // free output sections
     wasm.imports.deinit(gpa);
     wasm.func_types.deinit(gpa);
     wasm.functions.deinit(gpa);
     wasm.wasm_globals.deinit(gpa);
     wasm.function_table.deinit(gpa);
     wasm.tables.deinit(gpa);
     wasm.init_funcs.deinit(gpa);
     wasm.exports.deinit(gpa);
 
     wasm.string_table.deinit(gpa);
     wasm.synthetic_functions.deinit(gpa);
 }
 
 pub fn updateFunc(wasm: *Wasm, mod: *Module, func_index: InternPool.Index, air: Air, liveness: Liveness) !void {
     if (build_options.skip_non_native and builtin.object_format != .wasm) {
         @panic("Attempted to compile for object format that was disabled by build configuration");
     }
     if (wasm.llvm_object) |llvm_object| return llvm_object.updateFunc(mod, func_index, air, liveness);
     try wasm.zigObjectPtr().?.updateFunc(wasm, mod, func_index, air, liveness);
 }
 
 // Generate code for the Decl, storing it in memory to be later written to
 // the file on flush().
 pub fn updateDecl(wasm: *Wasm, mod: *Module, decl_index: InternPool.DeclIndex) !void {
     if (build_options.skip_non_native and builtin.object_format != .wasm) {
         @panic("Attempted to compile for object format that was disabled by build configuration");
     }
     if (wasm.llvm_object) |llvm_object| return llvm_object.updateDecl(mod, decl_index);
     try wasm.zigObjectPtr().?.updateDecl(wasm, mod, decl_index);
 }
 
 pub fn updateDeclLineNumber(wasm: *Wasm, mod: *Module, decl_index: InternPool.DeclIndex) !void {
     if (wasm.llvm_object) |_| return;
     try wasm.zigObjectPtr().?.updateDeclLineNumber(mod, decl_index);
 }
 
 /// From a given symbol location, returns its `wasm.GlobalType`.
 /// Asserts the Symbol represents a global.
 fn getGlobalType(wasm: *const Wasm, loc: SymbolLoc) std.wasm.GlobalType {
     const symbol = loc.getSymbol(wasm);
     assert(symbol.tag == .global);
     const is_undefined = symbol.isUndefined();
     if (wasm.file(loc.file)) |obj_file| {
         if (is_undefined) {
             return obj_file.import(loc.index).kind.global;
         }
         return obj_file.globals()[symbol.index - obj_file.importedGlobals()].global_type;
     }
     if (is_undefined) {
         return wasm.imports.get(loc).?.kind.global;
     }
     return wasm.wasm_globals.items[symbol.index].global_type;
 }
 
 /// From a given symbol location, returns its `wasm.Type`.
 /// Asserts the Symbol represents a function.
 fn getFunctionSignature(wasm: *const Wasm, loc: SymbolLoc) std.wasm.Type {
     const symbol = loc.getSymbol(wasm);
     assert(symbol.tag == .function);
     const is_undefined = symbol.isUndefined();
     if (wasm.file(loc.file)) |obj_file| {
         if (is_undefined) {
             const ty_index = obj_file.import(loc.index).kind.function;
             return obj_file.funcTypes()[ty_index];
         }
         const type_index = obj_file.function(loc.index).type_index;
         return obj_file.funcTypes()[type_index];
     }
     if (is_undefined) {
         const ty_index = wasm.imports.get(loc).?.kind.function;
         return wasm.func_types.items[ty_index];
     }
     return wasm.func_types.items[wasm.functions.get(.{ .file = loc.file, .index = symbol.index }).?.func.type_index];
 }
 
 /// Lowers a constant typed value to a local symbol and atom.
 /// Returns the symbol index of the local
 /// The given `decl` is the parent decl whom owns the constant.
 pub fn lowerUnnamedConst(wasm: *Wasm, tv: TypedValue, decl_index: InternPool.DeclIndex) !u32 {
     return wasm.zigObjectPtr().?.lowerUnnamedConst(wasm, tv, decl_index);
 }
 
 /// Returns the symbol index from a symbol of which its flag is set global,
 /// such as an exported or imported symbol.
 /// If the symbol does not yet exist, creates a new one symbol instead
 /// and then returns the index to it.
 pub fn getGlobalSymbol(wasm: *Wasm, name: []const u8, lib_name: ?[]const u8) !u32 {
     _ = lib_name;
     return wasm.zigObjectPtr().?.getGlobalSymbol(wasm.base.comp.gpa, name);
 }
 
 /// For a given decl, find the given symbol index's atom, and create a relocation for the type.
 /// Returns the given pointer address
 pub fn getDeclVAddr(
     wasm: *Wasm,
     decl_index: InternPool.DeclIndex,
     reloc_info: link.File.RelocInfo,
 ) !u64 {
     return wasm.zigObjectPtr().?.getDeclVAddr(wasm, decl_index, reloc_info);
 }
 
 pub fn lowerAnonDecl(
     wasm: *Wasm,
     decl_val: InternPool.Index,
     explicit_alignment: Alignment,
     src_loc: Module.SrcLoc,
 ) !codegen.Result {
     return wasm.zigObjectPtr().?.lowerAnonDecl(wasm, decl_val, explicit_alignment, src_loc);
 }
 
 pub fn getAnonDeclVAddr(wasm: *Wasm, decl_val: InternPool.Index, reloc_info: link.File.RelocInfo) !u64 {
     return wasm.zigObjectPtr().?.getAnonDeclVAddr(wasm, decl_val, reloc_info);
 }
 
 pub fn deleteDeclExport(
     wasm: *Wasm,
     decl_index: InternPool.DeclIndex,
     name: InternPool.NullTerminatedString,
 ) void {
     if (wasm.llvm_object) |_| return;
     return wasm.zigObjectPtr().?.deleteDeclExport(wasm, decl_index, name);
 }
 
 pub fn updateExports(
     wasm: *Wasm,
     mod: *Module,
     exported: Module.Exported,
     exports: []const *Module.Export,
 ) !void {
     if (build_options.skip_non_native and builtin.object_format != .wasm) {
         @panic("Attempted to compile for object format that was disabled by build configuration");
     }
     if (wasm.llvm_object) |llvm_object| return llvm_object.updateExports(mod, exported, exports);
     return wasm.zigObjectPtr().?.updateExports(wasm, mod, exported, exports);
 }
 
 pub fn freeDecl(wasm: *Wasm, decl_index: InternPool.DeclIndex) void {
     if (wasm.llvm_object) |llvm_object| return llvm_object.freeDecl(decl_index);
     return wasm.zigObjectPtr().?.freeDecl(wasm, decl_index);
 }
 
 /// Assigns indexes to all indirect functions.
 /// Starts at offset 1, where the value `0` represents an unresolved function pointer
 /// or null-pointer
 fn mapFunctionTable(wasm: *Wasm) void {
     var it = wasm.function_table.iterator();
     var index: u32 = 1;
     while (it.next()) |entry| {
         const symbol = entry.key_ptr.*.getSymbol(wasm);
         if (symbol.isAlive()) {
             entry.value_ptr.* = index;
             index += 1;
         } else {
             wasm.function_table.removeByPtr(entry.key_ptr);
         }
     }
 
     if (wasm.import_table or wasm.base.comp.config.output_mode == .Obj) {
         const sym_loc = wasm.findGlobalSymbol("__indirect_function_table").?;
         const import = wasm.imports.getPtr(sym_loc).?;
         import.kind.table.limits.min = index - 1; // we start at index 1.
     } else if (index > 1) {
         log.debug("Appending indirect function table", .{});
         const sym_loc = wasm.findGlobalSymbol("__indirect_function_table").?;
         const symbol = sym_loc.getSymbol(wasm);
         const table = &wasm.tables.items[symbol.index - wasm.imported_tables_count];
         table.limits = .{ .min = index, .max = index, .flags = 0x1 };
     }
 }
 
 /// From a given index, append the given `Atom` at the back of the linked list.
 /// Simply inserts it into the map of atoms when it doesn't exist yet.
 pub fn appendAtomAtIndex(wasm: *Wasm, index: u32, atom_index: Atom.Index) !void {
     const gpa = wasm.base.comp.gpa;
     const atom = wasm.getAtomPtr(atom_index);
     if (wasm.atoms.getPtr(index)) |last_index_ptr| {
         atom.prev = last_index_ptr.*;
         last_index_ptr.* = atom_index;
     } else {
         try wasm.atoms.putNoClobber(gpa, index, atom_index);
     }
 }
 
 fn allocateAtoms(wasm: *Wasm) !void {
     // first sort the data segments
     try sortDataSegments(wasm);
 
     var it = wasm.atoms.iterator();
     while (it.next()) |entry| {
         const segment = &wasm.segments.items[entry.key_ptr.*];
         var atom_index = entry.value_ptr.*;
         if (entry.key_ptr.* == wasm.code_section_index) {
             // Code section is allocated upon writing as they are required to be ordered
             // to synchronise with the function section.
             continue;
         }
         var offset: u32 = 0;
         while (true) {
             const atom = wasm.getAtomPtr(atom_index);
             const symbol_loc = atom.symbolLoc();
             // Ensure we get the original symbol, so we verify the correct symbol on whether
             // it is dead or not and ensure an atom is removed when dead.
             // This is required as we may have parsed aliases into atoms.
             const sym = if (wasm.file(symbol_loc.file)) |obj_file|
                 obj_file.symbol(symbol_loc.index).*
             else
                 wasm.synthetic_symbols.items[symbol_loc.index];
 
             // Dead symbols must be unlinked from the linked-list to prevent them
             // from being emit into the binary.
             if (sym.isDead()) {
                 if (entry.value_ptr.* == atom_index and atom.prev != null) {
                     // When the atom is dead and is also the first atom retrieved from wasm.atoms(index) we update
                     // the entry to point it to the previous atom to ensure we do not start with a dead symbol that
                     // was removed and therefore do not emit any code at all.
                     entry.value_ptr.* = atom.prev.?;
                 }
                 atom_index = atom.prev orelse break;
                 atom.prev = null;
                 continue;
             }
             offset = @intCast(atom.alignment.forward(offset));
             atom.offset = offset;
             log.debug("Atom '{s}' allocated from 0x{x:0>8} to 0x{x:0>8} size={d}", .{
                 symbol_loc.getName(wasm),
                 offset,
                 offset + atom.size,
                 atom.size,
             });
             offset += atom.size;
             atom_index = atom.prev orelse break;
         }
         segment.size = @intCast(segment.alignment.forward(offset));
     }
 }
 
 /// For each data symbol, sets the virtual address.
 fn allocateVirtualAddresses(wasm: *Wasm) void {
     for (wasm.resolved_symbols.keys()) |loc| {
         const symbol = loc.getSymbol(wasm);
         if (symbol.tag != .data or symbol.isDead()) {
             // Only data symbols have virtual addresses.
             // Dead symbols do not get allocated, so we don't need to set their virtual address either.
             continue;
         }
         const atom_index = wasm.symbol_atom.get(loc) orelse {
             // synthetic symbol that does not contain an atom
             continue;
         };
 
         const atom = wasm.getAtom(atom_index);
         const merge_segment = wasm.base.comp.config.output_mode != .Obj;
         const segment_info = if (atom.file != .null)
             wasm.file(atom.file).?.segmentInfo()
         else
             wasm.segment_info.values();
         const segment_name = segment_info[symbol.index].outputName(merge_segment);
         const segment_index = wasm.data_segments.get(segment_name).?;
         const segment = wasm.segments.items[segment_index];
 
         // TLS symbols have their virtual address set relative to their own TLS segment,
         // rather than the entire Data section.
         if (symbol.hasFlag(.WASM_SYM_TLS)) {
             symbol.virtual_address = atom.offset;
         } else {
             symbol.virtual_address = atom.offset + segment.offset;
         }
     }
 }
 
 fn sortDataSegments(wasm: *Wasm) !void {
     const gpa = wasm.base.comp.gpa;
     var new_mapping: std.StringArrayHashMapUnmanaged(u32) = .{};
     try new_mapping.ensureUnusedCapacity(gpa, wasm.data_segments.count());
     errdefer new_mapping.deinit(gpa);
 
     const keys = try gpa.dupe([]const u8, wasm.data_segments.keys());
     defer gpa.free(keys);
 
     const SortContext = struct {
         fn sort(_: void, lhs: []const u8, rhs: []const u8) bool {
             return order(lhs) < order(rhs);
         }
 
         fn order(name: []const u8) u8 {
             if (mem.startsWith(u8, name, ".rodata")) return 0;
             if (mem.startsWith(u8, name, ".data")) return 1;
             if (mem.startsWith(u8, name, ".text")) return 2;
             return 3;
         }
     };
 
     mem.sort([]const u8, keys, {}, SortContext.sort);
     for (keys) |key| {
         const segment_index = wasm.data_segments.get(key).?;
         new_mapping.putAssumeCapacity(key, segment_index);
     }
     wasm.data_segments.deinit(gpa);
     wasm.data_segments = new_mapping;
 }
 
 /// Obtains all initfuncs from each object file, verifies its function signature,
 /// and then appends it to our final `init_funcs` list.
 /// After all functions have been inserted, the functions will be ordered based
 /// on their priority.
 /// NOTE: This function must be called before we merged any other section.
 /// This is because all init funcs in the object files contain references to the
 /// original functions and their types. We need to know the type to verify it doesn't
 /// contain any parameters.
 fn setupInitFunctions(wasm: *Wasm) !void {
     const gpa = wasm.base.comp.gpa;
     // There's no constructors for Zig so we can simply search through linked object files only.
     for (wasm.objects.items) |file_index| {
         const object: Object = wasm.files.items(.data)[@intFromEnum(file_index)].object;
         try wasm.init_funcs.ensureUnusedCapacity(gpa, object.init_funcs.len);
         for (object.init_funcs) |init_func| {
             const symbol = object.symtable[init_func.symbol_index];
             const ty: std.wasm.Type = if (symbol.isUndefined()) ty: {
                 const imp: types.Import = object.findImport(symbol);
                 break :ty object.func_types[imp.kind.function];
             } else ty: {
                 const func_index = symbol.index - object.imported_functions_count;
                 const func = object.functions[func_index];
                 break :ty object.func_types[func.type_index];
             };
             if (ty.params.len != 0) {
                 log.err("constructor functions cannot take arguments: '{s}'", .{object.string_table.get(symbol.name)});
                 return error.InvalidInitFunc;
             }
             log.debug("appended init func '{s}'\n", .{object.string_table.get(symbol.name)});
             wasm.init_funcs.appendAssumeCapacity(.{
                 .index = init_func.symbol_index,
                 .file = file_index,
                 .priority = init_func.priority,
             });
             try wasm.mark(.{ .index = init_func.symbol_index, .file = file_index });
         }
     }
 
     // sort the initfunctions based on their priority
     mem.sort(InitFuncLoc, wasm.init_funcs.items, {}, InitFuncLoc.lessThan);
 
     if (wasm.init_funcs.items.len > 0) {
         const loc = wasm.findGlobalSymbol("__wasm_call_ctors").?;
         try wasm.mark(loc);
     }
 }
 
 /// Creates a function body for the `__wasm_call_ctors` symbol.
 /// Loops over all constructors found in `init_funcs` and calls them
 /// respectively based on their priority which was sorted by `setupInitFunctions`.
 /// NOTE: This function must be called after we merged all sections to ensure the
 /// references to the function stored in the symbol have been finalized so we end
 /// up calling the resolved function.
 fn initializeCallCtorsFunction(wasm: *Wasm) !void {
     const gpa = wasm.base.comp.gpa;
     // No code to emit, so also no ctors to call
     if (wasm.code_section_index == null) {
         // Make sure to remove it from the resolved symbols so we do not emit
         // it within any section. TODO: Remove this once we implement garbage collection.
         const loc = wasm.findGlobalSymbol("__wasm_call_ctors").?;
         assert(wasm.resolved_symbols.swapRemove(loc));
         return;
     }
 
     var function_body = std.ArrayList(u8).init(gpa);
     defer function_body.deinit();
     const writer = function_body.writer();
 
     // Create the function body
     {
         // Write locals count (we have none)
         try leb.writeULEB128(writer, @as(u32, 0));
 
         // call constructors
         for (wasm.init_funcs.items) |init_func_loc| {
             const symbol = init_func_loc.getSymbol(wasm);
             const func = wasm.functions.values()[symbol.index - wasm.imported_functions_count].func;
             const ty = wasm.func_types.items[func.type_index];
 
             // Call function by its function index
             try writer.writeByte(std.wasm.opcode(.call));
             try leb.writeULEB128(writer, symbol.index);
 
             // drop all returned values from the stack as __wasm_call_ctors has no return value
             for (ty.returns) |_| {
                 try writer.writeByte(std.wasm.opcode(.drop));
             }
         }
 
         // End function body
         try writer.writeByte(std.wasm.opcode(.end));
     }
 
     try wasm.createSyntheticFunction(
         "__wasm_call_ctors",
         std.wasm.Type{ .params = &.{}, .returns = &.{} },
         &function_body,
     );
 }
 
 fn createSyntheticFunction(
     wasm: *Wasm,
     symbol_name: []const u8,
     func_ty: std.wasm.Type,
     function_body: *std.ArrayList(u8),
 ) !void {
     const gpa = wasm.base.comp.gpa;
     const loc = wasm.findGlobalSymbol(symbol_name) orelse
         try wasm.createSyntheticSymbol(symbol_name, .function);
     const symbol = loc.getSymbol(wasm);
     if (symbol.isDead()) {
         return;
     }
     const ty_index = try wasm.putOrGetFuncType(func_ty);
     // create function with above type
     const func_index = wasm.imported_functions_count + @as(u32, @intCast(wasm.functions.count()));
     try wasm.functions.putNoClobber(
         gpa,
         .{ .file = .null, .index = func_index },
         .{ .func = .{ .type_index = ty_index }, .sym_index = loc.index },
     );
     symbol.index = func_index;
 
     // create the atom that will be output into the final binary
     const atom_index = try wasm.createAtom(loc.index, .null);
     const atom = wasm.getAtomPtr(atom_index);
     atom.size = @intCast(function_body.items.len);
     atom.code = function_body.moveToUnmanaged();
     try wasm.appendAtomAtIndex(wasm.code_section_index.?, atom_index);
 }
 
 /// Unlike `createSyntheticFunction` this function is to be called by
 /// the codegeneration backend. This will not allocate the created Atom yet.
 /// Returns the index of the symbol.
 pub fn createFunction(
     wasm: *Wasm,
     symbol_name: []const u8,
     func_ty: std.wasm.Type,
     function_body: *std.ArrayList(u8),
     relocations: *std.ArrayList(Relocation),
 ) !u32 {
     return wasm.zigObjectPtr().?.createFunction(wasm, symbol_name, func_ty, function_body, relocations);
 }
 
 /// If required, sets the function index in the `start` section.
 fn setupStartSection(wasm: *Wasm) !void {
     if (wasm.findGlobalSymbol("__wasm_init_memory")) |loc| {
         wasm.entry = loc.getSymbol(wasm).index;
     }
 }
 
 fn initializeTLSFunction(wasm: *Wasm) !void {
     const comp = wasm.base.comp;
     const gpa = comp.gpa;
     const shared_memory = comp.config.shared_memory;
 
     if (!shared_memory) return;
 
     var function_body = std.ArrayList(u8).init(gpa);
     defer function_body.deinit();
     const writer = function_body.writer();
 
     // locals
     try writer.writeByte(0);
 
     // If there's a TLS segment, initialize it during runtime using the bulk-memory feature
     if (wasm.data_segments.getIndex(".tdata")) |data_index| {
         const segment_index = wasm.data_segments.entries.items(.value)[data_index];
         const segment = wasm.segments.items[segment_index];
 
         const param_local: u32 = 0;
 
         try writer.writeByte(std.wasm.opcode(.local_get));
         try leb.writeULEB128(writer, param_local);
 
         const tls_base_loc = wasm.findGlobalSymbol("__tls_base").?;
         try writer.writeByte(std.wasm.opcode(.global_set));
         try leb.writeULEB128(writer, tls_base_loc.getSymbol(wasm).index);
 
         // load stack values for the bulk-memory operation
         {
             try writer.writeByte(std.wasm.opcode(.local_get));
             try leb.writeULEB128(writer, param_local);
 
             try writer.writeByte(std.wasm.opcode(.i32_const));
             try leb.writeULEB128(writer, @as(u32, 0)); //segment offset
 
             try writer.writeByte(std.wasm.opcode(.i32_const));
             try leb.writeULEB128(writer, @as(u32, segment.size)); //segment offset
         }
 
         // perform the bulk-memory operation to initialize the data segment
         try writer.writeByte(std.wasm.opcode(.misc_prefix));
         try leb.writeULEB128(writer, std.wasm.miscOpcode(.memory_init));
         // segment immediate
         try leb.writeULEB128(writer, @as(u32, @intCast(data_index)));
         // memory index immediate (always 0)
         try leb.writeULEB128(writer, @as(u32, 0));
     }
 
     // If we have to perform any TLS relocations, call the corresponding function
     // which performs all runtime TLS relocations. This is a synthetic function,
     // generated by the linker.
     if (wasm.findGlobalSymbol("__wasm_apply_global_tls_relocs")) |loc| {
         try writer.writeByte(std.wasm.opcode(.call));
         try leb.writeULEB128(writer, loc.getSymbol(wasm).index);
     }
 
     try writer.writeByte(std.wasm.opcode(.end));
 
     try wasm.createSyntheticFunction(
         "__wasm_init_tls",
         std.wasm.Type{ .params = &.{.i32}, .returns = &.{} },
         &function_body,
     );
 }
 
 fn setupImports(wasm: *Wasm) !void {
     const gpa = wasm.base.comp.gpa;
     log.debug("Merging imports", .{});
     for (wasm.resolved_symbols.keys()) |symbol_loc| {
         const obj_file = wasm.file(symbol_loc.file) orelse {
             // Synthetic symbols will already exist in the `import` section
             continue;
         };
 
         const symbol = symbol_loc.getSymbol(wasm);
         if (symbol.isDead() or
             !symbol.requiresImport() or
             std.mem.eql(u8, symbol_loc.getName(wasm), "__indirect_function_table"))
         {
             continue;
         }
 
         log.debug("Symbol '{s}' will be imported from the host", .{symbol_loc.getName(wasm)});
         const import = obj_file.import(symbol_loc.index);
 
         // We copy the import to a new import to ensure the names contain references
         // to the internal string table, rather than of the object file.
         const new_imp: types.Import = .{
             .module_name = try wasm.string_table.put(gpa, obj_file.string(import.module_name)),
             .name = try wasm.string_table.put(gpa, obj_file.string(import.name)),
             .kind = import.kind,
         };
         // TODO: De-duplicate imports when they contain the same names and type
         try wasm.imports.putNoClobber(gpa, symbol_loc, new_imp);
     }
 
     // Assign all indexes of the imports to their representing symbols
     var function_index: u32 = 0;
     var global_index: u32 = 0;
     var table_index: u32 = 0;
     var it = wasm.imports.iterator();
     while (it.next()) |entry| {
         const symbol = entry.key_ptr.*.getSymbol(wasm);
         const import: types.Import = entry.value_ptr.*;
         switch (import.kind) {
             .function => {
                 symbol.index = function_index;
                 function_index += 1;
             },
             .global => {
                 symbol.index = global_index;
                 global_index += 1;
             },
             .table => {
                 symbol.index = table_index;
                 table_index += 1;
             },
             else => unreachable,
         }
     }
     wasm.imported_functions_count = function_index;
     wasm.imported_globals_count = global_index;
     wasm.imported_tables_count = table_index;
 
     log.debug("Merged ({d}) functions, ({d}) globals, and ({d}) tables into import section", .{
         function_index,
         global_index,
         table_index,
     });
 }
 
 /// Takes the global, function and table section from each linked object file
 /// and merges it into a single section for each.
 fn mergeSections(wasm: *Wasm) !void {
     const gpa = wasm.base.comp.gpa;
 
     var removed_duplicates = std.ArrayList(SymbolLoc).init(gpa);
     defer removed_duplicates.deinit();
 
     for (wasm.resolved_symbols.keys()) |sym_loc| {
         const obj_file = wasm.file(sym_loc.file) orelse {
             // Zig code-generated symbols are already within the sections and do not
             // require to be merged
             continue;
         };
 
         const symbol = obj_file.symbol(sym_loc.index);
         if (symbol.isDead() or symbol.isUndefined()) {
             // Skip undefined symbols as they go in the `import` section
             continue;
         }
 
         switch (symbol.tag) {
             .function => {
                 const gop = try wasm.functions.getOrPut(
                     gpa,
                     .{ .file = sym_loc.file, .index = symbol.index },
                 );
                 if (gop.found_existing) {
                     // We found an alias to the same function, discard this symbol in favor of
                     // the original symbol and point the discard function to it. This ensures
                     // we only emit a single function, instead of duplicates.
                     symbol.unmark();
                     try wasm.discarded.putNoClobber(
                         gpa,
                         sym_loc,
                         .{ .file = gop.key_ptr.*.file, .index = gop.value_ptr.*.sym_index },
                     );
                     try removed_duplicates.append(sym_loc);
                     continue;
                 }
                 gop.value_ptr.* = .{ .func = obj_file.function(sym_loc.index), .sym_index = sym_loc.index };
                 symbol.index = @as(u32, @intCast(gop.index)) + wasm.imported_functions_count;
             },
             .global => {
                 const index = symbol.index - obj_file.importedFunctions();
                 const original_global = obj_file.globals()[index];
                 symbol.index = @as(u32, @intCast(wasm.wasm_globals.items.len)) + wasm.imported_globals_count;
                 try wasm.wasm_globals.append(gpa, original_global);
             },
             .table => {
                 const index = symbol.index - obj_file.importedFunctions();
                 // assert it's a regular relocatable object file as `ZigObject` will never
                 // contain a table.
                 const original_table = obj_file.object.tables[index];
                 symbol.index = @as(u32, @intCast(wasm.tables.items.len)) + wasm.imported_tables_count;
                 try wasm.tables.append(gpa, original_table);
             },
             else => {},
         }
     }
 
     // For any removed duplicates, remove them from the resolved symbols list
     for (removed_duplicates.items) |sym_loc| {
         assert(wasm.resolved_symbols.swapRemove(sym_loc));
     }
 
     log.debug("Merged ({d}) functions", .{wasm.functions.count()});
     log.debug("Merged ({d}) globals", .{wasm.wasm_globals.items.len});
     log.debug("Merged ({d}) tables", .{wasm.tables.items.len});
 }
 
 /// Merges function types of all object files into the final
 /// 'types' section, while assigning the type index to the representing
 /// section (import, export, function).
 fn mergeTypes(wasm: *Wasm) !void {
     const gpa = wasm.base.comp.gpa;
     // A map to track which functions have already had their
     // type inserted. If we do this for the same function multiple times,
     // it will be overwritten with the incorrect type.
     var dirty = std.AutoHashMap(u32, void).init(gpa);
     try dirty.ensureUnusedCapacity(@as(u32, @intCast(wasm.functions.count())));
     defer dirty.deinit();
 
     for (wasm.resolved_symbols.keys()) |sym_loc| {
         const obj_file = wasm.file(sym_loc.file) orelse {
             // zig code-generated symbols are already present in final type section
             continue;
         };
 
         const symbol = obj_file.symbol(sym_loc.index);
         if (symbol.tag != .function or symbol.isDead()) {
             // Only functions have types. Only retrieve the type of referenced functions.
             continue;
         }
 
         if (symbol.isUndefined()) {
             log.debug("Adding type from extern function '{s}'", .{sym_loc.getName(wasm)});
             const import: *types.Import = wasm.imports.getPtr(sym_loc) orelse continue;
             const original_type = obj_file.funcTypes()[import.kind.function];
             import.kind.function = try wasm.putOrGetFuncType(original_type);
         } else if (!dirty.contains(symbol.index)) {
             log.debug("Adding type from function '{s}'", .{sym_loc.getName(wasm)});
             const func = &wasm.functions.values()[symbol.index - wasm.imported_functions_count].func;
             func.type_index = try wasm.putOrGetFuncType(obj_file.funcTypes()[func.type_index]);
             dirty.putAssumeCapacityNoClobber(symbol.index, {});
         }
     }
     log.debug("Completed merging and deduplicating types. Total count: ({d})", .{wasm.func_types.items.len});
 }
 
 fn setupExports(wasm: *Wasm) !void {
     const comp = wasm.base.comp;
     const gpa = comp.gpa;
     if (comp.config.output_mode == .Obj) return;
     log.debug("Building exports from symbols", .{});
 
     const force_exp_names = wasm.export_symbol_names;
     if (force_exp_names.len > 0) {
         var failed_exports = false;
 
         for (force_exp_names) |exp_name| {
             const loc = wasm.findGlobalSymbol(exp_name) orelse {
                 log.err("could not export '{s}', symbol not found", .{exp_name});
                 failed_exports = true;
                 continue;
             };
 
             const symbol = loc.getSymbol(wasm);
             symbol.setFlag(.WASM_SYM_EXPORTED);
         }
 
         if (failed_exports) {
             return error.MissingSymbol;
         }
     }
 
     for (wasm.resolved_symbols.keys()) |sym_loc| {
         const symbol = sym_loc.getSymbol(wasm);
         if (!symbol.isExported(comp.config.rdynamic)) continue;
 
         const sym_name = sym_loc.getName(wasm);
         const export_name = if (wasm.export_names.get(sym_loc)) |name| name else blk: {
             if (sym_loc.file == .null) break :blk symbol.name;
             break :blk try wasm.string_table.put(gpa, sym_name);
         };
         const exp: types.Export = if (symbol.tag == .data) exp: {
             const global_index = @as(u32, @intCast(wasm.imported_globals_count + wasm.wasm_globals.items.len));
             try wasm.wasm_globals.append(gpa, .{
                 .global_type = .{ .valtype = .i32, .mutable = false },
                 .init = .{ .i32_const = @as(i32, @intCast(symbol.virtual_address)) },
             });
             break :exp .{
                 .name = export_name,
                 .kind = .global,
                 .index = global_index,
             };
         } else .{
             .name = export_name,
             .kind = symbol.tag.externalType(),
             .index = symbol.index,
         };
         log.debug("Exporting symbol '{s}' as '{s}' at index: ({d})", .{
             sym_name,
             wasm.string_table.get(exp.name),
             exp.index,
         });
         try wasm.exports.append(gpa, exp);
     }
 
     log.debug("Completed building exports. Total count: ({d})", .{wasm.exports.items.len});
 }
 
 fn setupStart(wasm: *Wasm) !void {
     const comp = wasm.base.comp;
     // do not export entry point if user set none or no default was set.
     const entry_name = wasm.entry_name orelse return;
 
     const symbol_loc = wasm.findGlobalSymbol(entry_name) orelse {
         log.err("Entry symbol '{s}' missing, use '-fno-entry' to suppress", .{entry_name});
         return error.MissingSymbol;
     };
 
     const symbol = symbol_loc.getSymbol(wasm);
     if (symbol.tag != .function) {
         log.err("Entry symbol '{s}' is not a function", .{entry_name});
         return error.InvalidEntryKind;
     }
 
     // Ensure the symbol is exported so host environment can access it
     if (comp.config.output_mode != .Obj) {
         symbol.setFlag(.WASM_SYM_EXPORTED);
     }
 }
 
 /// Sets up the memory section of the wasm module, as well as the stack.
 fn setupMemory(wasm: *Wasm) !void {
     const comp = wasm.base.comp;
     const shared_memory = comp.config.shared_memory;
     log.debug("Setting up memory layout", .{});
     const page_size = std.wasm.page_size; // 64kb
     const stack_alignment: Alignment = .@"16"; // wasm's stack alignment as specified by tool-convention
     const heap_alignment: Alignment = .@"16"; // wasm's heap alignment as specified by tool-convention
 
     // Always place the stack at the start by default
     // unless the user specified the global-base flag
     var place_stack_first = true;
     var memory_ptr: u64 = if (wasm.global_base) |base| blk: {
         place_stack_first = false;
         break :blk base;
     } else 0;
 
     const is_obj = comp.config.output_mode == .Obj;
 
     const stack_ptr = if (wasm.findGlobalSymbol("__stack_pointer")) |loc| index: {
         const sym = loc.getSymbol(wasm);
         break :index sym.index - wasm.imported_globals_count;
     } else null;
 
     if (place_stack_first and !is_obj) {
         memory_ptr = stack_alignment.forward(memory_ptr);
         memory_ptr += wasm.base.stack_size;
         // We always put the stack pointer global at index 0
         if (stack_ptr) |index| {
             wasm.wasm_globals.items[index].init.i32_const = @as(i32, @bitCast(@as(u32, @intCast(memory_ptr))));
         }
     }
 
     var offset: u32 = @as(u32, @intCast(memory_ptr));
     var data_seg_it = wasm.data_segments.iterator();
     while (data_seg_it.next()) |entry| {
         const segment = &wasm.segments.items[entry.value_ptr.*];
         memory_ptr = segment.alignment.forward(memory_ptr);
 
         // set TLS-related symbols
         if (mem.eql(u8, entry.key_ptr.*, ".tdata")) {
             if (wasm.findGlobalSymbol("__tls_size")) |loc| {
                 const sym = loc.getSymbol(wasm);
                 wasm.wasm_globals.items[sym.index - wasm.imported_globals_count].init.i32_const = @intCast(segment.size);
             }
             if (wasm.findGlobalSymbol("__tls_align")) |loc| {
                 const sym = loc.getSymbol(wasm);
                 wasm.wasm_globals.items[sym.index - wasm.imported_globals_count].init.i32_const = @intCast(segment.alignment.toByteUnitsOptional().?);
             }
             if (wasm.findGlobalSymbol("__tls_base")) |loc| {
                 const sym = loc.getSymbol(wasm);
                 wasm.wasm_globals.items[sym.index - wasm.imported_globals_count].init.i32_const = if (shared_memory)
                     @as(i32, 0)
                 else
                     @as(i32, @intCast(memory_ptr));
             }
         }
 
         memory_ptr += segment.size;
         segment.offset = offset;
         offset += segment.size;
     }
 
     // create the memory init flag which is used by the init memory function
     if (shared_memory and wasm.hasPassiveInitializationSegments()) {
         // align to pointer size
         memory_ptr = mem.alignForward(u64, memory_ptr, 4);
         const loc = try wasm.createSyntheticSymbol("__wasm_init_memory_flag", .data);
         const sym = loc.getSymbol(wasm);
         sym.virtual_address = @as(u32, @intCast(memory_ptr));
         memory_ptr += 4;
     }
 
     if (!place_stack_first and !is_obj) {
         memory_ptr = stack_alignment.forward(memory_ptr);
         memory_ptr += wasm.base.stack_size;
         if (stack_ptr) |index| {
             wasm.wasm_globals.items[index].init.i32_const = @as(i32, @bitCast(@as(u32, @intCast(memory_ptr))));
         }
     }
 
     // One of the linked object files has a reference to the __heap_base symbol.
     // We must set its virtual address so it can be used in relocations.
     if (wasm.findGlobalSymbol("__heap_base")) |loc| {
         const symbol = loc.getSymbol(wasm);
         symbol.virtual_address = @intCast(heap_alignment.forward(memory_ptr));
     }
 
     // Setup the max amount of pages
     // For now we only support wasm32 by setting the maximum allowed memory size 2^32-1
     const max_memory_allowed: u64 = (1 << 32) - 1;
 
     if (wasm.initial_memory) |initial_memory| {
         if (!std.mem.isAlignedGeneric(u64, initial_memory, page_size)) {
             log.err("Initial memory must be {d}-byte aligned", .{page_size});
             return error.MissAlignment;
         }
         if (memory_ptr > initial_memory) {
             log.err("Initial memory too small, must be at least {d} bytes", .{memory_ptr});
             return error.MemoryTooSmall;
         }
         if (initial_memory > max_memory_allowed) {
             log.err("Initial memory exceeds maximum memory {d}", .{max_memory_allowed});
             return error.MemoryTooBig;
         }
         memory_ptr = initial_memory;
     }
     memory_ptr = mem.alignForward(u64, memory_ptr, std.wasm.page_size);
     // In case we do not import memory, but define it ourselves,
     // set the minimum amount of pages on the memory section.
     wasm.memories.limits.min = @as(u32, @intCast(memory_ptr / page_size));
     log.debug("Total memory pages: {d}", .{wasm.memories.limits.min});
 
     if (wasm.findGlobalSymbol("__heap_end")) |loc| {
         const symbol = loc.getSymbol(wasm);
         symbol.virtual_address = @as(u32, @intCast(memory_ptr));
     }
 
     if (wasm.max_memory) |max_memory| {
         if (!std.mem.isAlignedGeneric(u64, max_memory, page_size)) {
             log.err("Maximum memory must be {d}-byte aligned", .{page_size});
             return error.MissAlignment;
         }
         if (memory_ptr > max_memory) {
             log.err("Maxmimum memory too small, must be at least {d} bytes", .{memory_ptr});
             return error.MemoryTooSmall;
         }
         if (max_memory > max_memory_allowed) {
             log.err("Maximum memory exceeds maxmium amount {d}", .{max_memory_allowed});
             return error.MemoryTooBig;
         }
         wasm.memories.limits.max = @as(u32, @intCast(max_memory / page_size));
         wasm.memories.limits.setFlag(.WASM_LIMITS_FLAG_HAS_MAX);
         if (shared_memory) {
             wasm.memories.limits.setFlag(.WASM_LIMITS_FLAG_IS_SHARED);
         }
         log.debug("Maximum memory pages: {?d}", .{wasm.memories.limits.max});
     }
 }
 
 /// From a given object's index and the index of the segment, returns the corresponding
 /// index of the segment within the final data section. When the segment does not yet
 /// exist, a new one will be initialized and appended. The new index will be returned in that case.
 pub fn getMatchingSegment(wasm: *Wasm, file_index: File.Index, symbol_index: u32) !u32 {
     const comp = wasm.base.comp;
     const gpa = comp.gpa;
     const obj_file = wasm.file(file_index).?;
     const symbol = obj_file.symbols()[symbol_index];
     const index: u32 = @intCast(wasm.segments.items.len);
     const shared_memory = comp.config.shared_memory;
 
     switch (symbol.tag) {
         .data => {
             const segment_info = obj_file.segmentInfo()[symbol.index];
             const merge_segment = comp.config.output_mode != .Obj;
             const result = try wasm.data_segments.getOrPut(gpa, segment_info.outputName(merge_segment));
             if (!result.found_existing) {
                 result.value_ptr.* = index;
                 var flags: u32 = 0;
                 if (shared_memory) {
                     flags |= @intFromEnum(Segment.Flag.WASM_DATA_SEGMENT_IS_PASSIVE);
                 }
                 try wasm.segments.append(gpa, .{
                     .alignment = .@"1",
                     .size = 0,
                     .offset = 0,
                     .flags = flags,
                 });
                 try wasm.segment_info.putNoClobber(gpa, index, .{
                     .name = try gpa.dupe(u8, segment_info.name),
                     .alignment = segment_info.alignment,
                     .flags = segment_info.flags,
                 });
                 return index;
             } else return result.value_ptr.*;
         },
         .function => return wasm.code_section_index orelse blk: {
             wasm.code_section_index = index;
             try wasm.appendDummySegment();
             break :blk index;
         },
         .section => {
             const section_name = obj_file.symbolName(symbol_index);
             if (mem.eql(u8, section_name, ".debug_info")) {
                 return wasm.debug_info_index orelse blk: {
                     wasm.debug_info_index = index;
                     try wasm.appendDummySegment();
                     break :blk index;
                 };
             } else if (mem.eql(u8, section_name, ".debug_line")) {
                 return wasm.debug_line_index orelse blk: {
                     wasm.debug_line_index = index;
                     try wasm.appendDummySegment();
                     break :blk index;
                 };
             } else if (mem.eql(u8, section_name, ".debug_loc")) {
                 return wasm.debug_loc_index orelse blk: {
                     wasm.debug_loc_index = index;
                     try wasm.appendDummySegment();
                     break :blk index;
                 };
             } else if (mem.eql(u8, section_name, ".debug_ranges")) {
                 return wasm.debug_ranges_index orelse blk: {
                     wasm.debug_ranges_index = index;
                     try wasm.appendDummySegment();
                     break :blk index;
                 };
             } else if (mem.eql(u8, section_name, ".debug_pubnames")) {
                 return wasm.debug_pubnames_index orelse blk: {
                     wasm.debug_pubnames_index = index;
                     try wasm.appendDummySegment();
                     break :blk index;
                 };
             } else if (mem.eql(u8, section_name, ".debug_pubtypes")) {
                 return wasm.debug_pubtypes_index orelse blk: {
                     wasm.debug_pubtypes_index = index;
                     try wasm.appendDummySegment();
                     break :blk index;
                 };
             } else if (mem.eql(u8, section_name, ".debug_abbrev")) {
                 return wasm.debug_abbrev_index orelse blk: {
                     wasm.debug_abbrev_index = index;
                     try wasm.appendDummySegment();
                     break :blk index;
                 };
             } else if (mem.eql(u8, section_name, ".debug_str")) {
                 return wasm.debug_str_index orelse blk: {
                     wasm.debug_str_index = index;
                     try wasm.appendDummySegment();
                     break :blk index;
                 };
             } else {
                 log.err("found unknown section '{s}'", .{section_name});
                 return error.UnexpectedValue;
             }
         },
         else => unreachable,
     }
 }
 
 /// Appends a new segment with default field values
 fn appendDummySegment(wasm: *Wasm) !void {
     const gpa = wasm.base.comp.gpa;
     try wasm.segments.append(gpa, .{
         .alignment = .@"1",
         .size = 0,
         .offset = 0,
         .flags = 0,
     });
 }
 
 fn resetState(wasm: *Wasm) void {
     const gpa = wasm.base.comp.gpa;
 
     for (wasm.segment_info.values()) |segment_info| {
         gpa.free(segment_info.name);
     }
 
     // TODO: Revisit
     // var atom_it = wasm.decls.valueIterator();
     // while (atom_it.next()) |atom_index| {
     //     const atom = wasm.getAtomPtr(atom_index.*);
     //     atom.next = null;
     //     atom.prev = null;
 
     //     for (atom.locals.items) |local_atom_index| {
     //         const local_atom = wasm.getAtomPtr(local_atom_index);
     //         local_atom.next = null;
     //         local_atom.prev = null;
     //     }
     // }
 
     wasm.functions.clearRetainingCapacity();
     wasm.exports.clearRetainingCapacity();
     wasm.segments.clearRetainingCapacity();
     wasm.segment_info.clearRetainingCapacity();
     wasm.data_segments.clearRetainingCapacity();
     wasm.atoms.clearRetainingCapacity();
     wasm.symbol_atom.clearRetainingCapacity();
     wasm.code_section_index = null;
     wasm.debug_info_index = null;
     wasm.debug_line_index = null;
     wasm.debug_loc_index = null;
     wasm.debug_str_index = null;
     wasm.debug_ranges_index = null;
     wasm.debug_abbrev_index = null;
     wasm.debug_pubnames_index = null;
     wasm.debug_pubtypes_index = null;
 }
 
 pub fn flush(wasm: *Wasm, arena: Allocator, prog_node: *std.Progress.Node) link.File.FlushError!void {
     const comp = wasm.base.comp;
     const use_lld = build_options.have_llvm and comp.config.use_lld;
     const use_llvm = comp.config.use_llvm;
 
     if (use_lld) {
         return wasm.linkWithLLD(arena, prog_node);
     } else if (use_llvm) {
         return wasm.linkWithZld(arena, prog_node);
     } else {
         return wasm.flushModule(arena, prog_node);
     }
 }
 
 /// Uses the in-house linker to link one or multiple object -and archive files into a WebAssembly binary.
 fn linkWithZld(wasm: *Wasm, arena: Allocator, prog_node: *std.Progress.Node) link.File.FlushError!void {
     const tracy = trace(@src());
     defer tracy.end();
 
     const comp = wasm.base.comp;
     const shared_memory = comp.config.shared_memory;
     const import_memory = comp.config.import_memory;
 
     const directory = wasm.base.emit.directory; // Just an alias to make it shorter to type.
     const full_out_path = try directory.join(arena, &[_][]const u8{wasm.base.emit.sub_path});
     const opt_zcu = comp.module;
     const use_llvm = comp.config.use_llvm;
 
     // If there is no Zig code to compile, then we should skip flushing the output file because it
     // will not be part of the linker line anyway.
     const module_obj_path: ?[]const u8 = if (opt_zcu != null) blk: {
         assert(use_llvm); // `linkWithZld` should never be called when the Wasm backend is used
         try wasm.flushModule(arena, prog_node);
 
         if (fs.path.dirname(full_out_path)) |dirname| {
             break :blk try fs.path.join(arena, &.{ dirname, wasm.base.zcu_object_sub_path.? });
         } else {
             break :blk wasm.base.zcu_object_sub_path.?;
         }
     } else null;
 
     var sub_prog_node = prog_node.start("Wasm Flush", 0);
     sub_prog_node.activate();
     defer sub_prog_node.end();
 
     const compiler_rt_path: ?[]const u8 = blk: {
         if (comp.compiler_rt_obj) |obj| break :blk obj.full_object_path;
         if (comp.compiler_rt_lib) |lib| break :blk lib.full_object_path;
         break :blk null;
     };
 
     const id_symlink_basename = "zld.id";
 
     var man: Cache.Manifest = undefined;
     defer if (!wasm.base.disable_lld_caching) man.deinit();
     var digest: [Cache.hex_digest_len]u8 = undefined;
 
     const objects = comp.objects;
 
     // NOTE: The following section must be maintained to be equal
     // as the section defined in `linkWithLLD`
     if (!wasm.base.disable_lld_caching) {
         man = comp.cache_parent.obtain();
 
         // We are about to obtain this lock, so here we give other processes a chance first.
         wasm.base.releaseLock();
 
         comptime assert(Compilation.link_hash_implementation_version == 12);
 
         for (objects) |obj| {
             _ = try man.addFile(obj.path, null);
             man.hash.add(obj.must_link);
         }
         for (comp.c_object_table.keys()) |key| {
             _ = try man.addFile(key.status.success.object_path, null);
         }
         try man.addOptionalFile(module_obj_path);
         try man.addOptionalFile(compiler_rt_path);
         man.hash.addOptionalBytes(wasm.entry_name);
         man.hash.add(wasm.base.stack_size);
         man.hash.add(wasm.base.build_id);
         man.hash.add(import_memory);
         man.hash.add(shared_memory);
         man.hash.add(wasm.import_table);
         man.hash.add(wasm.export_table);
         man.hash.addOptional(wasm.initial_memory);
         man.hash.addOptional(wasm.max_memory);
         man.hash.addOptional(wasm.global_base);
         man.hash.addListOfBytes(wasm.export_symbol_names);
         // strip does not need to go into the linker hash because it is part of the hash namespace
 
         // We don't actually care whether it's a cache hit or miss; we just need the digest and the lock.
         _ = try man.hit();
         digest = man.final();
 
         var prev_digest_buf: [digest.len]u8 = undefined;
         const prev_digest: []u8 = Cache.readSmallFile(
             directory.handle,
             id_symlink_basename,
             &prev_digest_buf,
         ) catch |err| blk: {
             log.debug("WASM LLD new_digest={s} error: {s}", .{ std.fmt.fmtSliceHexLower(&digest), @errorName(err) });
             // Handle this as a cache miss.
             break :blk prev_digest_buf[0..0];
         };
         if (mem.eql(u8, prev_digest, &digest)) {
             log.debug("WASM LLD digest={s} match - skipping invocation", .{std.fmt.fmtSliceHexLower(&digest)});
             // Hot diggity dog! The output binary is already there.
             wasm.base.lock = man.toOwnedLock();
             return;
         }
         log.debug("WASM LLD prev_digest={s} new_digest={s}", .{ std.fmt.fmtSliceHexLower(prev_digest), std.fmt.fmtSliceHexLower(&digest) });
 
         // We are about to change the output file to be different, so we invalidate the build hash now.
         directory.handle.deleteFile(id_symlink_basename) catch |err| switch (err) {
             error.FileNotFound => {},
             else => |e| return e,
         };
     }
 
     // Positional arguments to the linker such as object files and static archives.
     var positionals = std.ArrayList([]const u8).init(arena);
     try positionals.ensureUnusedCapacity(objects.len);
 
     const target = comp.root_mod.resolved_target.result;
     const output_mode = comp.config.output_mode;
     const link_mode = comp.config.link_mode;
     const link_libc = comp.config.link_libc;
     const link_libcpp = comp.config.link_libcpp;
     const wasi_exec_model = comp.config.wasi_exec_model;
 
     // When the target os is WASI, we allow linking with WASI-LIBC
     if (target.os.tag == .wasi) {
         const is_exe_or_dyn_lib = output_mode == .Exe or
             (output_mode == .Lib and link_mode == .Dynamic);
         if (is_exe_or_dyn_lib) {
             for (comp.wasi_emulated_libs) |crt_file| {
                 try positionals.append(try comp.get_libc_crt_file(
                     arena,
                     wasi_libc.emulatedLibCRFileLibName(crt_file),
                 ));
             }
 
             if (link_libc) {
                 try positionals.append(try comp.get_libc_crt_file(
                     arena,
                     wasi_libc.execModelCrtFileFullName(wasi_exec_model),
                 ));
                 try positionals.append(try comp.get_libc_crt_file(arena, "libc.a"));
             }
 
             if (link_libcpp) {
                 try positionals.append(comp.libcxx_static_lib.?.full_object_path);
                 try positionals.append(comp.libcxxabi_static_lib.?.full_object_path);
             }
         }
     }
 
     if (module_obj_path) |path| {
         try positionals.append(path);
     }
 
     for (objects) |object| {
         try positionals.append(object.path);
     }
 
     for (comp.c_object_table.keys()) |c_object| {
         try positionals.append(c_object.status.success.object_path);
     }
 
     if (comp.compiler_rt_lib) |lib| try positionals.append(lib.full_object_path);
     if (comp.compiler_rt_obj) |obj| try positionals.append(obj.full_object_path);
 
     try wasm.parseInputFiles(positionals.items);
 
     for (wasm.objects.items) |object_index| {
         try wasm.resolveSymbolsInObject(object_index);
     }
 
     var emit_features_count: u32 = 0;
     var enabled_features: [@typeInfo(types.Feature.Tag).Enum.fields.len]bool = undefined;
     try wasm.validateFeatures(&enabled_features, &emit_features_count);
     try wasm.resolveSymbolsInArchives();
     try wasm.resolveLazySymbols();
     try wasm.checkUndefinedSymbols();
 
     try wasm.setupInitFunctions();
     try wasm.setupStart();
 
     try wasm.markReferences();
     try wasm.setupImports();
     try wasm.mergeSections();
     try wasm.mergeTypes();
     try wasm.allocateAtoms();
     try wasm.setupMemory();
     wasm.allocateVirtualAddresses();
     wasm.mapFunctionTable();
     try wasm.initializeCallCtorsFunction();
     try wasm.setupInitMemoryFunction();
     try wasm.setupTLSRelocationsFunction();
     try wasm.initializeTLSFunction();
     try wasm.setupStartSection();
     try wasm.setupExports();
     try wasm.writeToFile(enabled_features, emit_features_count, arena);
 
     if (!wasm.base.disable_lld_caching) {
         // Update the file with the digest. If it fails we can continue; it only
         // means that the next invocation will have an unnecessary cache miss.
         Cache.writeSmallFile(directory.handle, id_symlink_basename, &digest) catch |err| {
             log.warn("failed to save linking hash digest symlink: {s}", .{@errorName(err)});
         };
         // Again failure here only means an unnecessary cache miss.
         man.writeManifest() catch |err| {
             log.warn("failed to write cache manifest when linking: {s}", .{@errorName(err)});
         };
         // We hang on to this lock so that the output file path can be used without
         // other processes clobbering it.
         wasm.base.lock = man.toOwnedLock();
     }
 }
 
 pub fn flushModule(wasm: *Wasm, arena: Allocator, prog_node: *std.Progress.Node) link.File.FlushError!void {
     const tracy = trace(@src());
     defer tracy.end();
 
     const comp = wasm.base.comp;
 
     if (wasm.llvm_object) |llvm_object| {
         try wasm.base.emitLlvmObject(arena, llvm_object, prog_node);
         return;
     }
 
     var sub_prog_node = prog_node.start("Wasm Flush", 0);
     sub_prog_node.activate();
     defer sub_prog_node.end();
 
     // ensure the error names table is populated when an error name is referenced
     // try wasm.populateErrorNameTable();
 
     const objects = comp.objects;
 
     // Positional arguments to the linker such as object files and static archives.
     var positionals = std.ArrayList([]const u8).init(arena);
     try positionals.ensureUnusedCapacity(objects.len);
 
     for (objects) |object| {
         positionals.appendAssumeCapacity(object.path);
     }
 
     for (comp.c_object_table.keys()) |c_object| {
         try positionals.append(c_object.status.success.object_path);
     }
 
     if (comp.compiler_rt_lib) |lib| try positionals.append(lib.full_object_path);
     if (comp.compiler_rt_obj) |obj| try positionals.append(obj.full_object_path);
 
     try wasm.parseInputFiles(positionals.items);
 
     if (wasm.zig_object_index != .null) {
         try wasm.resolveSymbolsInObject(wasm.zig_object_index);
     }
     for (wasm.objects.items) |object_index| {
         try wasm.resolveSymbolsInObject(object_index);
     }
 
     var emit_features_count: u32 = 0;
     var enabled_features: [@typeInfo(types.Feature.Tag).Enum.fields.len]bool = undefined;
     try wasm.validateFeatures(&enabled_features, &emit_features_count);
     try wasm.resolveSymbolsInArchives();
     try wasm.resolveLazySymbols();
     try wasm.checkUndefinedSymbols();
 
     // When we finish/error we reset the state of the linker
     // So we can rebuild the binary file on each incremental update
     defer wasm.resetState();
     try wasm.setupInitFunctions();
     try wasm.setupStart();
     try wasm.markReferences();
     // try wasm.setupErrorsLen();
     try wasm.setupImports();
     // if (comp.module) |mod| {
     //     var decl_it = wasm.decls.iterator();
     //     while (decl_it.next()) |entry| {
     //         const decl = mod.declPtr(entry.key_ptr.*);
     //         if (decl.isExtern(mod)) continue;
     //         const atom_index = entry.value_ptr.*;
     //         const atom = wasm.getAtomPtr(atom_index);
     //         if (decl.ty.zigTypeTag(mod) == .Fn) {
     //             try wasm.parseAtom(atom_index, .function);
     //         } else if (decl.getOwnedVariable(mod)) |variable| {
     //             if (variable.is_const) {
     //                 try wasm.parseAtom(atom_index, .{ .data = .read_only });
     //             } else if (Value.fromInterned(variable.init).isUndefDeep(mod)) {
     //                 // for safe build modes, we store the atom in the data segment,
     //                 // whereas for unsafe build modes we store it in bss.
     //                 const decl_namespace = mod.namespacePtr(decl.src_namespace);
     //                 const optimize_mode = decl_namespace.file_scope.mod.optimize_mode;
     //                 const is_initialized = switch (optimize_mode) {
     //                     .Debug, .ReleaseSafe => true,
     //                     .ReleaseFast, .ReleaseSmall => false,
     //                 };
     //                 try wasm.parseAtom(atom_index, .{ .data = if (is_initialized) .initialized else .uninitialized });
     //             } else {
     //                 // when the decl is all zeroes, we store the atom in the bss segment,
     //                 // in all other cases it will be in the data segment.
     //                 const is_zeroes = for (atom.code.items) |byte| {
     //                     if (byte != 0) break false;
     //                 } else true;
     //                 try wasm.parseAtom(atom_index, .{ .data = if (is_zeroes) .uninitialized else .initialized });
     //             }
     //         } else {
     //             try wasm.parseAtom(atom_index, .{ .data = .read_only });
     //         }
 
     //         // also parse atoms for a decl's locals
     //         for (atom.locals.items) |local_atom_index| {
     //             try wasm.parseAtom(local_atom_index, .{ .data = .read_only });
     //         }
     //     }
     //     // parse anonymous declarations
     //     for (wasm.anon_decls.keys(), wasm.anon_decls.values()) |decl_val, atom_index| {
     //         const ty = Type.fromInterned(mod.intern_pool.typeOf(decl_val));
     //         if (ty.zigTypeTag(mod) == .Fn) {
     //             try wasm.parseAtom(atom_index, .function);
     //         } else {
     //             try wasm.parseAtom(atom_index, .{ .data = .read_only });
     //         }
     //     }
 
     //     // also parse any backend-generated functions
     //     for (wasm.synthetic_functions.items) |atom_index| {
     //         try wasm.parseAtom(atom_index, .function);
     //     }
 
     //     if (wasm.dwarf) |*dwarf| {
     //         try dwarf.flushModule(comp.module.?);
     //     }
     // }
 
     try wasm.mergeSections();
     try wasm.mergeTypes();
     try wasm.allocateAtoms();
     try wasm.setupMemory();
     wasm.allocateVirtualAddresses();
     wasm.mapFunctionTable();
     try wasm.initializeCallCtorsFunction();
     try wasm.setupInitMemoryFunction();
     try wasm.setupTLSRelocationsFunction();
     try wasm.initializeTLSFunction();
     try wasm.setupStartSection();
     try wasm.setupExports();
     try wasm.writeToFile(enabled_features, emit_features_count, arena);
 }
 
 /// Writes the WebAssembly in-memory module to the file
 fn writeToFile(
     wasm: *Wasm,
     enabled_features: [@typeInfo(types.Feature.Tag).Enum.fields.len]bool,
     feature_count: u32,
     arena: Allocator,
 ) !void {
     const comp = wasm.base.comp;
     const gpa = comp.gpa;
     const use_llvm = comp.config.use_llvm;
     const use_lld = build_options.have_llvm and comp.config.use_lld;
     const shared_memory = comp.config.shared_memory;
     const import_memory = comp.config.import_memory;
     const export_memory = comp.config.export_memory;
 
     // Size of each section header
     const header_size = 5 + 1;
     // The amount of sections that will be written
     var section_count: u32 = 0;
     // Index of the code section. Used to tell relocation table where the section lives.
     var code_section_index: ?u32 = null;
     // Index of the data section. Used to tell relocation table where the section lives.
     var data_section_index: ?u32 = null;
     const is_obj = comp.config.output_mode == .Obj or (!use_llvm and use_lld);
 
     var binary_bytes = std.ArrayList(u8).init(gpa);
     defer binary_bytes.deinit();
     const binary_writer = binary_bytes.writer();
 
     // We write the magic bytes at the end so they will only be written
     // if everything succeeded as expected. So populate with 0's for now.
     try binary_writer.writeAll(&[_]u8{0} ** 8);
     // (Re)set file pointer to 0
     try wasm.base.file.?.setEndPos(0);
     try wasm.base.file.?.seekTo(0);
 
     // Type section
     if (wasm.func_types.items.len != 0) {
         const header_offset = try reserveVecSectionHeader(&binary_bytes);
         log.debug("Writing type section. Count: ({d})", .{wasm.func_types.items.len});
         for (wasm.func_types.items) |func_type| {
             try leb.writeULEB128(binary_writer, std.wasm.function_type);
             try leb.writeULEB128(binary_writer, @as(u32, @intCast(func_type.params.len)));
             for (func_type.params) |param_ty| {
                 try leb.writeULEB128(binary_writer, std.wasm.valtype(param_ty));
             }
             try leb.writeULEB128(binary_writer, @as(u32, @intCast(func_type.returns.len)));
             for (func_type.returns) |ret_ty| {
                 try leb.writeULEB128(binary_writer, std.wasm.valtype(ret_ty));
             }
         }
 
         try writeVecSectionHeader(
             binary_bytes.items,
             header_offset,
             .type,
             @intCast(binary_bytes.items.len - header_offset - header_size),
             @intCast(wasm.func_types.items.len),
         );
         section_count += 1;
     }
 
     // Import section
     if (wasm.imports.count() != 0 or import_memory) {
         const header_offset = try reserveVecSectionHeader(&binary_bytes);
 
         var it = wasm.imports.iterator();
         while (it.next()) |entry| {
             assert(entry.key_ptr.*.getSymbol(wasm).isUndefined());
             const import = entry.value_ptr.*;
             try wasm.emitImport(binary_writer, import);
         }
 
         if (import_memory) {
             const mem_name = if (is_obj) "__linear_memory" else "memory";
             const mem_imp: types.Import = .{
                 .module_name = try wasm.string_table.put(gpa, wasm.host_name),
                 .name = try wasm.string_table.put(gpa, mem_name),
                 .kind = .{ .memory = wasm.memories.limits },
             };
             try wasm.emitImport(binary_writer, mem_imp);
         }
 
         try writeVecSectionHeader(
             binary_bytes.items,
             header_offset,
             .import,
             @intCast(binary_bytes.items.len - header_offset - header_size),
             @intCast(wasm.imports.count() + @intFromBool(import_memory)),
         );
         section_count += 1;
     }
 
     // Function section
     if (wasm.functions.count() != 0) {
         const header_offset = try reserveVecSectionHeader(&binary_bytes);
         for (wasm.functions.values()) |function| {
             try leb.writeULEB128(binary_writer, function.func.type_index);
         }
 
         try writeVecSectionHeader(
             binary_bytes.items,
             header_offset,
             .function,
             @intCast(binary_bytes.items.len - header_offset - header_size),
             @intCast(wasm.functions.count()),
         );
         section_count += 1;
     }
 
     // Table section
     if (wasm.tables.items.len > 0) {
         const header_offset = try reserveVecSectionHeader(&binary_bytes);
 
         for (wasm.tables.items) |table| {
             try leb.writeULEB128(binary_writer, std.wasm.reftype(table.reftype));
             try emitLimits(binary_writer, table.limits);
         }
 
         try writeVecSectionHeader(
             binary_bytes.items,
             header_offset,
             .table,
             @intCast(binary_bytes.items.len - header_offset - header_size),
             @intCast(wasm.tables.items.len),
         );
         section_count += 1;
     }
 
     // Memory section
     if (!import_memory) {
         const header_offset = try reserveVecSectionHeader(&binary_bytes);
 
         try emitLimits(binary_writer, wasm.memories.limits);
         try writeVecSectionHeader(
             binary_bytes.items,
             header_offset,
             .memory,
             @intCast(binary_bytes.items.len - header_offset - header_size),
             1, // wasm currently only supports 1 linear memory segment
         );
         section_count += 1;
     }
 
     // Global section (used to emit stack pointer)
     if (wasm.wasm_globals.items.len > 0) {
         const header_offset = try reserveVecSectionHeader(&binary_bytes);
 
         for (wasm.wasm_globals.items) |global| {
             try binary_writer.writeByte(std.wasm.valtype(global.global_type.valtype));
             try binary_writer.writeByte(@intFromBool(global.global_type.mutable));
             try emitInit(binary_writer, global.init);
         }
 
         try writeVecSectionHeader(
             binary_bytes.items,
             header_offset,
             .global,
             @intCast(binary_bytes.items.len - header_offset - header_size),
             @intCast(wasm.wasm_globals.items.len),
         );
         section_count += 1;
     }
 
     // Export section
     if (wasm.exports.items.len != 0 or export_memory) {
         const header_offset = try reserveVecSectionHeader(&binary_bytes);
 
         for (wasm.exports.items) |exp| {
             const name = wasm.string_table.get(exp.name);
             try leb.writeULEB128(binary_writer, @as(u32, @intCast(name.len)));
             try binary_writer.writeAll(name);
             try leb.writeULEB128(binary_writer, @intFromEnum(exp.kind));
             try leb.writeULEB128(binary_writer, exp.index);
         }
 
         if (export_memory) {
             try leb.writeULEB128(binary_writer, @as(u32, @intCast("memory".len)));
             try binary_writer.writeAll("memory");
             try binary_writer.writeByte(std.wasm.externalKind(.memory));
             try leb.writeULEB128(binary_writer, @as(u32, 0));
         }
 
         try writeVecSectionHeader(
             binary_bytes.items,
             header_offset,
             .@"export",
             @intCast(binary_bytes.items.len - header_offset - header_size),
             @intCast(wasm.exports.items.len + @intFromBool(export_memory)),
         );
         section_count += 1;
     }
 
     if (wasm.entry) |entry_index| {
         const header_offset = try reserveVecSectionHeader(&binary_bytes);
         try writeVecSectionHeader(
             binary_bytes.items,
             header_offset,
             .start,
             @intCast(binary_bytes.items.len - header_offset - header_size),
             entry_index,
         );
     }
 
     // element section (function table)
     if (wasm.function_table.count() > 0) {
         const header_offset = try reserveVecSectionHeader(&binary_bytes);
 
         const table_loc = wasm.findGlobalSymbol("__indirect_function_table").?;
         const table_sym = table_loc.getSymbol(wasm);
 
         const flags: u32 = if (table_sym.index == 0) 0x0 else 0x02; // passive with implicit 0-index table or set table index manually
         try leb.writeULEB128(binary_writer, flags);
         if (flags == 0x02) {
             try leb.writeULEB128(binary_writer, table_sym.index);
         }
         try emitInit(binary_writer, .{ .i32_const = 1 }); // We start at index 1, so unresolved function pointers are invalid
         if (flags == 0x02) {
             try leb.writeULEB128(binary_writer, @as(u8, 0)); // represents funcref
         }
         try leb.writeULEB128(binary_writer, @as(u32, @intCast(wasm.function_table.count())));
         var symbol_it = wasm.function_table.keyIterator();
         while (symbol_it.next()) |symbol_loc_ptr| {
             const sym = symbol_loc_ptr.*.getSymbol(wasm);
             try leb.writeULEB128(binary_writer, sym.index);
         }
 
         try writeVecSectionHeader(
             binary_bytes.items,
             header_offset,
             .element,
             @intCast(binary_bytes.items.len - header_offset - header_size),
             1,
         );
         section_count += 1;
     }
 
     // When the shared-memory option is enabled, we *must* emit the 'data count' section.
     const data_segments_count = wasm.data_segments.count() - @intFromBool(wasm.data_segments.contains(".bss") and !import_memory);
     if (data_segments_count != 0 and shared_memory) {
         const header_offset = try reserveVecSectionHeader(&binary_bytes);
         try writeVecSectionHeader(
             binary_bytes.items,
             header_offset,
             .data_count,
             @intCast(binary_bytes.items.len - header_offset - header_size),
             @intCast(data_segments_count),
         );
     }
 
     // Code section
     if (wasm.code_section_index != null) {
         const header_offset = try reserveVecSectionHeader(&binary_bytes);
         const start_offset = binary_bytes.items.len - 5; // minus 5 so start offset is 5 to include entry count
 
         var func_it = wasm.functions.iterator();
         while (func_it.next()) |entry| {
             const sym_loc: SymbolLoc = .{ .index = entry.value_ptr.sym_index, .file = entry.key_ptr.file };
             const atom_index = wasm.symbol_atom.get(sym_loc).?;
             const atom = wasm.getAtomPtr(atom_index);
 
             if (!is_obj) {
                 atom.resolveRelocs(wasm);
             }
             atom.offset = @intCast(binary_bytes.items.len - start_offset);
             try leb.writeULEB128(binary_writer, atom.size);
             try binary_writer.writeAll(atom.code.items);
         }
 
         try writeVecSectionHeader(
             binary_bytes.items,
             header_offset,
             .code,
             @intCast(binary_bytes.items.len - header_offset - header_size),
             @intCast(wasm.functions.count()),
         );
         code_section_index = section_count;
         section_count += 1;
     }
 
     // Data section
     if (data_segments_count != 0) {
         const header_offset = try reserveVecSectionHeader(&binary_bytes);
 
         var it = wasm.data_segments.iterator();
         var segment_count: u32 = 0;
         while (it.next()) |entry| {
             // do not output 'bss' section unless we import memory and therefore
             // want to guarantee the data is zero initialized
             if (!import_memory and std.mem.eql(u8, entry.key_ptr.*, ".bss")) continue;
             const segment_index = entry.value_ptr.*;
             const segment = wasm.segments.items[segment_index];
             if (segment.size == 0) continue; // do not emit empty segments
             segment_count += 1;
             var atom_index = wasm.atoms.get(segment_index).?;
 
             try leb.writeULEB128(binary_writer, segment.flags);
             if (segment.flags & @intFromEnum(Wasm.Segment.Flag.WASM_DATA_SEGMENT_HAS_MEMINDEX) != 0) {
                 try leb.writeULEB128(binary_writer, @as(u32, 0)); // memory is always index 0 as we only have 1 memory entry
             }
             // when a segment is passive, it's initialized during runtime.
             if (!segment.isPassive()) {
                 try emitInit(binary_writer, .{ .i32_const = @as(i32, @bitCast(segment.offset)) });
             }
             // offset into data section
             try leb.writeULEB128(binary_writer, segment.size);
 
             // fill in the offset table and the data segments
             var current_offset: u32 = 0;
             while (true) {
                 const atom = wasm.getAtomPtr(atom_index);
                 if (!is_obj) {
                     atom.resolveRelocs(wasm);
                 }
 
                 // Pad with zeroes to ensure all segments are aligned
                 if (current_offset != atom.offset) {
                     const diff = atom.offset - current_offset;
                     try binary_writer.writeByteNTimes(0, diff);
                     current_offset += diff;
                 }
                 assert(current_offset == atom.offset);
                 assert(atom.code.items.len == atom.size);
                 try binary_writer.writeAll(atom.code.items);
 
                 current_offset += atom.size;
                 if (atom.prev) |prev| {
                     atom_index = prev;
                 } else {
                     // also pad with zeroes when last atom to ensure
                     // segments are aligned.
                     if (current_offset != segment.size) {
                         try binary_writer.writeByteNTimes(0, segment.size - current_offset);
                         current_offset += segment.size - current_offset;
                     }
                     break;
                 }
             }
             assert(current_offset == segment.size);
         }
 
         try writeVecSectionHeader(
             binary_bytes.items,
             header_offset,
             .data,
             @intCast(binary_bytes.items.len - header_offset - header_size),
             @intCast(segment_count),
         );
         data_section_index = section_count;
         section_count += 1;
     }
 
     if (is_obj) {
         // relocations need to point to the index of a symbol in the final symbol table. To save memory,
         // we never store all symbols in a single table, but store a location reference instead.
         // This means that for a relocatable object file, we need to generate one and provide it to the relocation sections.
         var symbol_table = std.AutoArrayHashMap(SymbolLoc, u32).init(arena);
         try wasm.emitLinkSection(&binary_bytes, &symbol_table);
         if (code_section_index) |code_index| {
             try wasm.emitCodeRelocations(&binary_bytes, code_index, symbol_table);
         }
         if (data_section_index) |data_index| {
             try wasm.emitDataRelocations(&binary_bytes, data_index, symbol_table);
         }
     } else if (comp.config.debug_format != .strip) {
         try wasm.emitNameSection(&binary_bytes, arena);
     }
 
     if (comp.config.debug_format != .strip) {
         // The build id must be computed on the main sections only,
         // so we have to do it now, before the debug sections.
         switch (wasm.base.build_id) {
             .none => {},
             .fast => {
                 var id: [16]u8 = undefined;
                 std.crypto.hash.sha3.TurboShake128(null).hash(binary_bytes.items, &id, .{});
                 var uuid: [36]u8 = undefined;
                 _ = try std.fmt.bufPrint(&uuid, "{s}-{s}-{s}-{s}-{s}", .{
                     std.fmt.fmtSliceHexLower(id[0..4]),
                     std.fmt.fmtSliceHexLower(id[4..6]),
                     std.fmt.fmtSliceHexLower(id[6..8]),
                     std.fmt.fmtSliceHexLower(id[8..10]),
                     std.fmt.fmtSliceHexLower(id[10..]),
                 });
                 try emitBuildIdSection(&binary_bytes, &uuid);
             },
             .hexstring => |hs| {
                 var buffer: [32 * 2]u8 = undefined;
                 const str = std.fmt.bufPrint(&buffer, "{s}", .{
                     std.fmt.fmtSliceHexLower(hs.toSlice()),
                 }) catch unreachable;
                 try emitBuildIdSection(&binary_bytes, str);
             },
             else => |mode| log.err("build-id '{s}' is not supported for WASM", .{@tagName(mode)}),
         }
 
         var debug_bytes = std.ArrayList(u8).init(gpa);
         defer debug_bytes.deinit();
 
         const DebugSection = struct {
             name: []const u8,
             index: ?u32,
         };
 
         const debug_sections: []const DebugSection = &.{
             .{ .name = ".debug_info", .index = wasm.debug_info_index },
             .{ .name = ".debug_pubtypes", .index = wasm.debug_pubtypes_index },
             .{ .name = ".debug_abbrev", .index = wasm.debug_abbrev_index },
             .{ .name = ".debug_line", .index = wasm.debug_line_index },
             .{ .name = ".debug_str", .index = wasm.debug_str_index },
             .{ .name = ".debug_pubnames", .index = wasm.debug_pubnames_index },
             .{ .name = ".debug_loc", .index = wasm.debug_loc_index },
             .{ .name = ".debug_ranges", .index = wasm.debug_ranges_index },
         };
 
         for (debug_sections) |item| {
             if (item.index) |index| {
                 var atom = wasm.getAtomPtr(wasm.atoms.get(index).?);
                 while (true) {
                     atom.resolveRelocs(wasm);
                     try debug_bytes.appendSlice(atom.code.items);
                     atom = if (atom.prev) |prev| wasm.getAtomPtr(prev) else break;
                 }
                 try emitDebugSection(&binary_bytes, debug_bytes.items, item.name);
                 debug_bytes.clearRetainingCapacity();
             }
         }
 
         try emitProducerSection(&binary_bytes);
         if (feature_count > 0) {
             try emitFeaturesSection(&binary_bytes, &enabled_features, feature_count);
         }
     }
 
     // Only when writing all sections executed properly we write the magic
     // bytes. This allows us to easily detect what went wrong while generating
     // the final binary.
     {
         const src = std.wasm.magic ++ std.wasm.version;
         binary_bytes.items[0..src.len].* = src;
     }
 
     // finally, write the entire binary into the file.
     var iovec = [_]std.os.iovec_const{.{
         .iov_base = binary_bytes.items.ptr,
         .iov_len = binary_bytes.items.len,
     }};
     try wasm.base.file.?.writevAll(&iovec);
 }
 
 fn emitDebugSection(binary_bytes: *std.ArrayList(u8), data: []const u8, name: []const u8) !void {
     if (data.len == 0) return;
     const header_offset = try reserveCustomSectionHeader(binary_bytes);
     const writer = binary_bytes.writer();
     try leb.writeULEB128(writer, @as(u32, @intCast(name.len)));
     try writer.writeAll(name);
 
     const start = binary_bytes.items.len - header_offset;
     log.debug("Emit debug section: '{s}' start=0x{x:0>8} end=0x{x:0>8}", .{ name, start, start + data.len });
     try writer.writeAll(data);
 
     try writeCustomSectionHeader(
         binary_bytes.items,
         header_offset,
         @as(u32, @intCast(binary_bytes.items.len - header_offset - 6)),
     );
 }
 
 fn emitProducerSection(binary_bytes: *std.ArrayList(u8)) !void {
     const header_offset = try reserveCustomSectionHeader(binary_bytes);
 
     const writer = binary_bytes.writer();
     const producers = "producers";
     try leb.writeULEB128(writer, @as(u32, @intCast(producers.len)));
     try writer.writeAll(producers);
 
     try leb.writeULEB128(writer, @as(u32, 2)); // 2 fields: Language + processed-by
 
     // used for the Zig version
     var version_buf: [100]u8 = undefined;
     const version = try std.fmt.bufPrint(&version_buf, "{}", .{build_options.semver});
 
     // language field
     {
         const language = "language";
         try leb.writeULEB128(writer, @as(u32, @intCast(language.len)));
         try writer.writeAll(language);
 
         // field_value_count (TODO: Parse object files for producer sections to detect their language)
         try leb.writeULEB128(writer, @as(u32, 1));
 
         // versioned name
         {
             try leb.writeULEB128(writer, @as(u32, 3)); // len of "Zig"
             try writer.writeAll("Zig");
 
             try leb.writeULEB128(writer, @as(u32, @intCast(version.len)));
             try writer.writeAll(version);
         }
     }
 
     // processed-by field
     {
         const processed_by = "processed-by";
         try leb.writeULEB128(writer, @as(u32, @intCast(processed_by.len)));
         try writer.writeAll(processed_by);
 
         // field_value_count (TODO: Parse object files for producer sections to detect other used tools)
         try leb.writeULEB128(writer, @as(u32, 1));
 
         // versioned name
         {
             try leb.writeULEB128(writer, @as(u32, 3)); // len of "Zig"
             try writer.writeAll("Zig");
 
             try leb.writeULEB128(writer, @as(u32, @intCast(version.len)));
             try writer.writeAll(version);
         }
     }
 
     try writeCustomSectionHeader(
         binary_bytes.items,
         header_offset,
         @as(u32, @intCast(binary_bytes.items.len - header_offset - 6)),
     );
 }
 
 fn emitBuildIdSection(binary_bytes: *std.ArrayList(u8), build_id: []const u8) !void {
     const header_offset = try reserveCustomSectionHeader(binary_bytes);
 
     const writer = binary_bytes.writer();
     const hdr_build_id = "build_id";
     try leb.writeULEB128(writer, @as(u32, @intCast(hdr_build_id.len)));
     try writer.writeAll(hdr_build_id);
 
     try leb.writeULEB128(writer, @as(u32, 1));
     try leb.writeULEB128(writer, @as(u32, @intCast(build_id.len)));
     try writer.writeAll(build_id);
 
     try writeCustomSectionHeader(
         binary_bytes.items,
         header_offset,
         @as(u32, @intCast(binary_bytes.items.len - header_offset - 6)),
     );
 }
 
 fn emitFeaturesSection(binary_bytes: *std.ArrayList(u8), enabled_features: []const bool, features_count: u32) !void {
     const header_offset = try reserveCustomSectionHeader(binary_bytes);
 
     const writer = binary_bytes.writer();
     const target_features = "target_features";
     try leb.writeULEB128(writer, @as(u32, @intCast(target_features.len)));
     try writer.writeAll(target_features);
 
     try leb.writeULEB128(writer, features_count);
     for (enabled_features, 0..) |enabled, feature_index| {
         if (enabled) {
             const feature: types.Feature = .{ .prefix = .used, .tag = @as(types.Feature.Tag, @enumFromInt(feature_index)) };
             try leb.writeULEB128(writer, @intFromEnum(feature.prefix));
             var buf: [100]u8 = undefined;
             const string = try std.fmt.bufPrint(&buf, "{}", .{feature.tag});
             try leb.writeULEB128(writer, @as(u32, @intCast(string.len)));
             try writer.writeAll(string);
         }
     }
 
     try writeCustomSectionHeader(
         binary_bytes.items,
         header_offset,
         @as(u32, @intCast(binary_bytes.items.len - header_offset - 6)),
     );
 }
 
 fn emitNameSection(wasm: *Wasm, binary_bytes: *std.ArrayList(u8), arena: std.mem.Allocator) !void {
     const comp = wasm.base.comp;
     const import_memory = comp.config.import_memory;
     const Name = struct {
         index: u32,
         name: []const u8,
 
         fn lessThan(context: void, lhs: @This(), rhs: @This()) bool {
             _ = context;
             return lhs.index < rhs.index;
         }
     };
 
     // we must de-duplicate symbols that point to the same function
     var funcs = std.AutoArrayHashMap(u32, Name).init(arena);
     try funcs.ensureUnusedCapacity(wasm.functions.count() + wasm.imported_functions_count);
     var globals = try std.ArrayList(Name).initCapacity(arena, wasm.wasm_globals.items.len + wasm.imported_globals_count);
     var segments = try std.ArrayList(Name).initCapacity(arena, wasm.data_segments.count());
 
     for (wasm.resolved_symbols.keys()) |sym_loc| {
         const symbol = sym_loc.getSymbol(wasm).*;
         if (symbol.isDead()) {
             continue;
         }
         const name = sym_loc.getName(wasm);
         switch (symbol.tag) {
             .function => {
                 const gop = funcs.getOrPutAssumeCapacity(symbol.index);
                 if (!gop.found_existing) {
                     gop.value_ptr.* = .{ .index = symbol.index, .name = name };
                 }
             },
             .global => globals.appendAssumeCapacity(.{ .index = symbol.index, .name = name }),
             else => {},
         }
     }
     // data segments are already 'ordered'
     var data_segment_index: u32 = 0;
     for (wasm.data_segments.keys()) |key| {
         // bss section is not emitted when this condition holds true, so we also
         // do not output a name for it.
         if (!import_memory and std.mem.eql(u8, key, ".bss")) continue;
         segments.appendAssumeCapacity(.{ .index = data_segment_index, .name = key });
         data_segment_index += 1;
     }
 
     mem.sort(Name, funcs.values(), {}, Name.lessThan);
     mem.sort(Name, globals.items, {}, Name.lessThan);
 
     const header_offset = try reserveCustomSectionHeader(binary_bytes);
     const writer = binary_bytes.writer();
     try leb.writeULEB128(writer, @as(u32, @intCast("name".len)));
     try writer.writeAll("name");
 
     try wasm.emitNameSubsection(.function, funcs.values(), writer);
     try wasm.emitNameSubsection(.global, globals.items, writer);
     try wasm.emitNameSubsection(.data_segment, segments.items, writer);
 
     try writeCustomSectionHeader(
         binary_bytes.items,
         header_offset,
         @as(u32, @intCast(binary_bytes.items.len - header_offset - 6)),
     );
 }
 
 fn emitNameSubsection(wasm: *Wasm, section_id: std.wasm.NameSubsection, names: anytype, writer: anytype) !void {
     const gpa = wasm.base.comp.gpa;
 
     // We must emit subsection size, so first write to a temporary list
     var section_list = std.ArrayList(u8).init(gpa);
     defer section_list.deinit();
     const sub_writer = section_list.writer();
 
     try leb.writeULEB128(sub_writer, @as(u32, @intCast(names.len)));
     for (names) |name| {
         log.debug("Emit symbol '{s}' type({s})", .{ name.name, @tagName(section_id) });
         try leb.writeULEB128(sub_writer, name.index);
         try leb.writeULEB128(sub_writer, @as(u32, @intCast(name.name.len)));
         try sub_writer.writeAll(name.name);
     }
 
     // From now, write to the actual writer
     try leb.writeULEB128(writer, @intFromEnum(section_id));
     try leb.writeULEB128(writer, @as(u32, @intCast(section_list.items.len)));
     try writer.writeAll(section_list.items);
 }
 
 fn emitLimits(writer: anytype, limits: std.wasm.Limits) !void {
     try writer.writeByte(limits.flags);
     try leb.writeULEB128(writer, limits.min);
     if (limits.hasFlag(.WASM_LIMITS_FLAG_HAS_MAX)) {
         try leb.writeULEB128(writer, limits.max);
     }
 }
 
 fn emitInit(writer: anytype, init_expr: std.wasm.InitExpression) !void {
     switch (init_expr) {
         .i32_const => |val| {
             try writer.writeByte(std.wasm.opcode(.i32_const));
             try leb.writeILEB128(writer, val);
         },
         .i64_const => |val| {
             try writer.writeByte(std.wasm.opcode(.i64_const));
             try leb.writeILEB128(writer, val);
         },
         .f32_const => |val| {
             try writer.writeByte(std.wasm.opcode(.f32_const));
             try writer.writeInt(u32, @bitCast(val), .little);
         },
         .f64_const => |val| {
             try writer.writeByte(std.wasm.opcode(.f64_const));
             try writer.writeInt(u64, @bitCast(val), .little);
         },
         .global_get => |val| {
             try writer.writeByte(std.wasm.opcode(.global_get));
             try leb.writeULEB128(writer, val);
         },
     }
     try writer.writeByte(std.wasm.opcode(.end));
 }
 
 fn emitImport(wasm: *Wasm, writer: anytype, import: types.Import) !void {
     const module_name = wasm.string_table.get(import.module_name);
     try leb.writeULEB128(writer, @as(u32, @intCast(module_name.len)));
     try writer.writeAll(module_name);
 
     const name = wasm.string_table.get(import.name);
     try leb.writeULEB128(writer, @as(u32, @intCast(name.len)));
     try writer.writeAll(name);
 
     try writer.writeByte(@intFromEnum(import.kind));
     switch (import.kind) {
         .function => |type_index| try leb.writeULEB128(writer, type_index),
         .global => |global_type| {
             try leb.writeULEB128(writer, std.wasm.valtype(global_type.valtype));
             try writer.writeByte(@intFromBool(global_type.mutable));
         },
         .table => |table| {
             try leb.writeULEB128(writer, std.wasm.reftype(table.reftype));
             try emitLimits(writer, table.limits);
         },
         .memory => |limits| {
             try emitLimits(writer, limits);
         },
     }
 }
 
 fn linkWithLLD(wasm: *Wasm, arena: Allocator, prog_node: *std.Progress.Node) !void {
     const tracy = trace(@src());
     defer tracy.end();
 
     const comp = wasm.base.comp;
     const shared_memory = comp.config.shared_memory;
     const export_memory = comp.config.export_memory;
     const import_memory = comp.config.import_memory;
     const target = comp.root_mod.resolved_target.result;
 
     const gpa = comp.gpa;
 
     const directory = wasm.base.emit.directory; // Just an alias to make it shorter to type.
     const full_out_path = try directory.join(arena, &[_][]const u8{wasm.base.emit.sub_path});
 
     // If there is no Zig code to compile, then we should skip flushing the output file because it
     // will not be part of the linker line anyway.
     const module_obj_path: ?[]const u8 = if (comp.module != null) blk: {
         try wasm.flushModule(arena, prog_node);
 
         if (fs.path.dirname(full_out_path)) |dirname| {
             break :blk try fs.path.join(arena, &.{ dirname, wasm.base.zcu_object_sub_path.? });
         } else {
             break :blk wasm.base.zcu_object_sub_path.?;
         }
     } else null;
 
     var sub_prog_node = prog_node.start("LLD Link", 0);
     sub_prog_node.activate();
     sub_prog_node.context.refresh();
     defer sub_prog_node.end();
 
     const is_obj = comp.config.output_mode == .Obj;
     const compiler_rt_path: ?[]const u8 = blk: {
         if (comp.compiler_rt_lib) |lib| break :blk lib.full_object_path;
         if (comp.compiler_rt_obj) |obj| break :blk obj.full_object_path;
         break :blk null;
     };
 
     const id_symlink_basename = "lld.id";
 
     var man: Cache.Manifest = undefined;
     defer if (!wasm.base.disable_lld_caching) man.deinit();
 
     var digest: [Cache.hex_digest_len]u8 = undefined;
 
     if (!wasm.base.disable_lld_caching) {
         man = comp.cache_parent.obtain();
 
         // We are about to obtain this lock, so here we give other processes a chance first.
         wasm.base.releaseLock();
 
         comptime assert(Compilation.link_hash_implementation_version == 12);
 
         for (comp.objects) |obj| {
             _ = try man.addFile(obj.path, null);
             man.hash.add(obj.must_link);
         }
         for (comp.c_object_table.keys()) |key| {
             _ = try man.addFile(key.status.success.object_path, null);
         }
         try man.addOptionalFile(module_obj_path);
         try man.addOptionalFile(compiler_rt_path);
         man.hash.addOptionalBytes(wasm.entry_name);
         man.hash.add(wasm.base.stack_size);
         man.hash.add(wasm.base.build_id);
         man.hash.add(import_memory);
         man.hash.add(export_memory);
         man.hash.add(wasm.import_table);
         man.hash.add(wasm.export_table);
         man.hash.addOptional(wasm.initial_memory);
         man.hash.addOptional(wasm.max_memory);
         man.hash.add(shared_memory);
         man.hash.addOptional(wasm.global_base);
         man.hash.addListOfBytes(wasm.export_symbol_names);
         // strip does not need to go into the linker hash because it is part of the hash namespace
 
         // We don't actually care whether it's a cache hit or miss; we just need the digest and the lock.
         _ = try man.hit();
         digest = man.final();
 
         var prev_digest_buf: [digest.len]u8 = undefined;
         const prev_digest: []u8 = Cache.readSmallFile(
             directory.handle,
             id_symlink_basename,
             &prev_digest_buf,
         ) catch |err| blk: {
             log.debug("WASM LLD new_digest={s} error: {s}", .{ std.fmt.fmtSliceHexLower(&digest), @errorName(err) });
             // Handle this as a cache miss.
             break :blk prev_digest_buf[0..0];
         };
         if (mem.eql(u8, prev_digest, &digest)) {
             log.debug("WASM LLD digest={s} match - skipping invocation", .{std.fmt.fmtSliceHexLower(&digest)});
             // Hot diggity dog! The output binary is already there.
             wasm.base.lock = man.toOwnedLock();
             return;
         }
         log.debug("WASM LLD prev_digest={s} new_digest={s}", .{ std.fmt.fmtSliceHexLower(prev_digest), std.fmt.fmtSliceHexLower(&digest) });
 
         // We are about to change the output file to be different, so we invalidate the build hash now.
         directory.handle.deleteFile(id_symlink_basename) catch |err| switch (err) {
             error.FileNotFound => {},
             else => |e| return e,
         };
     }
 
     if (is_obj) {
         // LLD's WASM driver does not support the equivalent of `-r` so we do a simple file copy
         // here. TODO: think carefully about how we can avoid this redundant operation when doing
         // build-obj. See also the corresponding TODO in linkAsArchive.
         const the_object_path = blk: {
             if (comp.objects.len != 0)
                 break :blk comp.objects[0].path;
 
             if (comp.c_object_table.count() != 0)
                 break :blk comp.c_object_table.keys()[0].status.success.object_path;
 
             if (module_obj_path) |p|
                 break :blk p;
 
             // TODO I think this is unreachable. Audit this situation when solving the above TODO
             // regarding eliding redundant object -> object transformations.
             return error.NoObjectsToLink;
         };
         // This can happen when using --enable-cache and using the stage1 backend. In this case
         // we can skip the file copy.
         if (!mem.eql(u8, the_object_path, full_out_path)) {
             try fs.cwd().copyFile(the_object_path, fs.cwd(), full_out_path, .{});
         }
     } else {
         // Create an LLD command line and invoke it.
         var argv = std.ArrayList([]const u8).init(gpa);
         defer argv.deinit();
         // We will invoke ourselves as a child process to gain access to LLD.
         // This is necessary because LLD does not behave properly as a library -
         // it calls exit() and does not reset all global data between invocations.
         const linker_command = "wasm-ld";
         try argv.appendSlice(&[_][]const u8{ comp.self_exe_path.?, linker_command });
         try argv.append("--error-limit=0");
 
         if (comp.config.lto) {
             switch (comp.root_mod.optimize_mode) {
                 .Debug => {},
                 .ReleaseSmall => try argv.append("-O2"),
                 .ReleaseFast, .ReleaseSafe => try argv.append("-O3"),
             }
         }
 
         if (import_memory) {
             try argv.append("--import-memory");
         }
 
         if (export_memory) {
             try argv.append("--export-memory");
         }
 
         if (wasm.import_table) {
             assert(!wasm.export_table);
             try argv.append("--import-table");
         }
 
         if (wasm.export_table) {
             assert(!wasm.import_table);
             try argv.append("--export-table");
         }
 
         // For wasm-ld we only need to specify '--no-gc-sections' when the user explicitly
         // specified it as garbage collection is enabled by default.
         if (!wasm.base.gc_sections) {
             try argv.append("--no-gc-sections");
         }
 
         if (comp.config.debug_format == .strip) {
             try argv.append("-s");
         }
 
         if (wasm.initial_memory) |initial_memory| {
             const arg = try std.fmt.allocPrint(arena, "--initial-memory={d}", .{initial_memory});
             try argv.append(arg);
         }
 
         if (wasm.max_memory) |max_memory| {
             const arg = try std.fmt.allocPrint(arena, "--max-memory={d}", .{max_memory});
             try argv.append(arg);
         }
 
         if (shared_memory) {
             try argv.append("--shared-memory");
         }
 
         if (wasm.global_base) |global_base| {
             const arg = try std.fmt.allocPrint(arena, "--global-base={d}", .{global_base});
             try argv.append(arg);
         } else {
             // We prepend it by default, so when a stack overflow happens the runtime will trap correctly,
             // rather than silently overwrite all global declarations. See https://github.com/ziglang/zig/issues/4496
             //
             // The user can overwrite this behavior by setting the global-base
             try argv.append("--stack-first");
         }
 
         // Users are allowed to specify which symbols they want to export to the wasm host.
         for (wasm.export_symbol_names) |symbol_name| {
             const arg = try std.fmt.allocPrint(arena, "--export={s}", .{symbol_name});
             try argv.append(arg);
         }
 
         if (comp.config.rdynamic) {
             try argv.append("--export-dynamic");
         }
 
         if (wasm.entry_name) |entry_name| {
             try argv.appendSlice(&.{ "--entry", entry_name });
         } else {
             try argv.append("--no-entry");
         }
 
         try argv.appendSlice(&.{
             "-z",
             try std.fmt.allocPrint(arena, "stack-size={d}", .{wasm.base.stack_size}),
         });
 
         if (wasm.import_symbols) {
             try argv.append("--allow-undefined");
         }
 
         if (comp.config.output_mode == .Lib and comp.config.link_mode == .Dynamic) {
             try argv.append("--shared");
         }
         if (comp.config.pie) {
             try argv.append("--pie");
         }
 
         // XXX - TODO: add when wasm-ld supports --build-id.
         // if (wasm.base.build_id) {
         //     try argv.append("--build-id=tree");
         // }
 
         try argv.appendSlice(&.{ "-o", full_out_path });
 
         if (target.cpu.arch == .wasm64) {
             try argv.append("-mwasm64");
         }
 
         if (target.os.tag == .wasi) {
             const is_exe_or_dyn_lib = comp.config.output_mode == .Exe or
                 (comp.config.output_mode == .Lib and comp.config.link_mode == .Dynamic);
             if (is_exe_or_dyn_lib) {
                 for (comp.wasi_emulated_libs) |crt_file| {
                     try argv.append(try comp.get_libc_crt_file(
                         arena,
                         wasi_libc.emulatedLibCRFileLibName(crt_file),
                     ));
                 }
 
                 if (comp.config.link_libc) {
                     try argv.append(try comp.get_libc_crt_file(
                         arena,
                         wasi_libc.execModelCrtFileFullName(comp.config.wasi_exec_model),
                     ));
                     try argv.append(try comp.get_libc_crt_file(arena, "libc.a"));
                 }
 
                 if (comp.config.link_libcpp) {
                     try argv.append(comp.libcxx_static_lib.?.full_object_path);
                     try argv.append(comp.libcxxabi_static_lib.?.full_object_path);
                 }
             }
         }
 
         // Positional arguments to the linker such as object files.
         var whole_archive = false;
         for (comp.objects) |obj| {
             if (obj.must_link and !whole_archive) {
                 try argv.append("-whole-archive");
                 whole_archive = true;
             } else if (!obj.must_link and whole_archive) {
                 try argv.append("-no-whole-archive");
                 whole_archive = false;
             }
             try argv.append(obj.path);
         }
         if (whole_archive) {
             try argv.append("-no-whole-archive");
             whole_archive = false;
         }
 
         for (comp.c_object_table.keys()) |key| {
             try argv.append(key.status.success.object_path);
         }
         if (module_obj_path) |p| {
             try argv.append(p);
         }
 
         if (comp.config.output_mode != .Obj and
             !comp.skip_linker_dependencies and
             !comp.config.link_libc)
         {
             try argv.append(comp.libc_static_lib.?.full_object_path);
         }
 
         if (compiler_rt_path) |p| {
             try argv.append(p);
         }
 
         if (comp.verbose_link) {
             // Skip over our own name so that the LLD linker name is the first argv item.
             Compilation.dump_argv(argv.items[1..]);
         }
 
         if (std.process.can_spawn) {
             // If possible, we run LLD as a child process because it does not always
             // behave properly as a library, unfortunately.
             // https://github.com/ziglang/zig/issues/3825
             var child = std.ChildProcess.init(argv.items, arena);
             if (comp.clang_passthrough_mode) {
                 child.stdin_behavior = .Inherit;
                 child.stdout_behavior = .Inherit;
                 child.stderr_behavior = .Inherit;
 
                 const term = child.spawnAndWait() catch |err| {
                     log.err("unable to spawn {s}: {s}", .{ argv.items[0], @errorName(err) });
                     return error.UnableToSpawnWasm;
                 };
                 switch (term) {
                     .Exited => |code| {
                         if (code != 0) {
                             std.process.exit(code);
                         }
                     },
                     else => std.process.abort(),
                 }
             } else {
                 child.stdin_behavior = .Ignore;
                 child.stdout_behavior = .Ignore;
                 child.stderr_behavior = .Pipe;
 
                 try child.spawn();
 
                 const stderr = try child.stderr.?.reader().readAllAlloc(arena, std.math.maxInt(usize));
 
                 const term = child.wait() catch |err| {
                     log.err("unable to spawn {s}: {s}", .{ argv.items[0], @errorName(err) });
                     return error.UnableToSpawnWasm;
                 };
 
                 switch (term) {
                     .Exited => |code| {
                         if (code != 0) {
                             comp.lockAndParseLldStderr(linker_command, stderr);
                             return error.LLDReportedFailure;
                         }
                     },
                     else => {
                         log.err("{s} terminated with stderr:\n{s}", .{ argv.items[0], stderr });
                         return error.LLDCrashed;
                     },
                 }
 
                 if (stderr.len != 0) {
                     log.warn("unexpected LLD stderr:\n{s}", .{stderr});
                 }
             }
         } else {
             const exit_code = try lldMain(arena, argv.items, false);
             if (exit_code != 0) {
                 if (comp.clang_passthrough_mode) {
                     std.process.exit(exit_code);
                 } else {
                     return error.LLDReportedFailure;
                 }
             }
         }
 
         // Give +x to the .wasm file if it is an executable and the OS is WASI.
         // Some systems may be configured to execute such binaries directly. Even if that
         // is not the case, it means we will get "exec format error" when trying to run
         // it, and then can react to that in the same way as trying to run an ELF file
         // from a foreign CPU architecture.
         if (fs.has_executable_bit and target.os.tag == .wasi and
             comp.config.output_mode == .Exe)
         {
             // TODO: what's our strategy for reporting linker errors from this function?
             // report a nice error here with the file path if it fails instead of
             // just returning the error code.
             // chmod does not interact with umask, so we use a conservative -rwxr--r-- here.
             std.os.fchmodat(fs.cwd().fd, full_out_path, 0o744, 0) catch |err| switch (err) {
                 error.OperationNotSupported => unreachable, // Not a symlink.
                 else => |e| return e,
             };
         }
     }
 
     if (!wasm.base.disable_lld_caching) {
         // Update the file with the digest. If it fails we can continue; it only
         // means that the next invocation will have an unnecessary cache miss.
         Cache.writeSmallFile(directory.handle, id_symlink_basename, &digest) catch |err| {
             log.warn("failed to save linking hash digest symlink: {s}", .{@errorName(err)});
         };
         // Again failure here only means an unnecessary cache miss.
         man.writeManifest() catch |err| {
             log.warn("failed to write cache manifest when linking: {s}", .{@errorName(err)});
         };
         // We hang on to this lock so that the output file path can be used without
         // other processes clobbering it.
         wasm.base.lock = man.toOwnedLock();
     }
 }
 
 fn reserveVecSectionHeader(bytes: *std.ArrayList(u8)) !u32 {
     // section id + fixed leb contents size + fixed leb vector length
     const header_size = 1 + 5 + 5;
     const offset = @as(u32, @intCast(bytes.items.len));
     try bytes.appendSlice(&[_]u8{0} ** header_size);
     return offset;
 }
 
 fn reserveCustomSectionHeader(bytes: *std.ArrayList(u8)) !u32 {
     // unlike regular section, we don't emit the count
     const header_size = 1 + 5;
     const offset = @as(u32, @intCast(bytes.items.len));
     try bytes.appendSlice(&[_]u8{0} ** header_size);
     return offset;
 }
 
 fn writeVecSectionHeader(buffer: []u8, offset: u32, section: std.wasm.Section, size: u32, items: u32) !void {
     var buf: [1 + 5 + 5]u8 = undefined;
     buf[0] = @intFromEnum(section);
     leb.writeUnsignedFixed(5, buf[1..6], size);
     leb.writeUnsignedFixed(5, buf[6..], items);
     buffer[offset..][0..buf.len].* = buf;
 }
 
 fn writeCustomSectionHeader(buffer: []u8, offset: u32, size: u32) !void {
     var buf: [1 + 5]u8 = undefined;
     buf[0] = 0; // 0 = 'custom' section
     leb.writeUnsignedFixed(5, buf[1..6], size);
     buffer[offset..][0..buf.len].* = buf;
 }
 
 fn emitLinkSection(wasm: *Wasm, binary_bytes: *std.ArrayList(u8), symbol_table: *std.AutoArrayHashMap(SymbolLoc, u32)) !void {
     const offset = try reserveCustomSectionHeader(binary_bytes);
     const writer = binary_bytes.writer();
     // emit "linking" custom section name
     const section_name = "linking";
     try leb.writeULEB128(writer, section_name.len);
     try writer.writeAll(section_name);
 
     // meta data version, which is currently '2'
     try leb.writeULEB128(writer, @as(u32, 2));
 
     // For each subsection type (found in types.Subsection) we can emit a section.
     // Currently, we only support emitting segment info and the symbol table.
     try wasm.emitSymbolTable(binary_bytes, symbol_table);
     try wasm.emitSegmentInfo(binary_bytes);
 
     const size: u32 = @intCast(binary_bytes.items.len - offset - 6);
     try writeCustomSectionHeader(binary_bytes.items, offset, size);
 }
 
 fn emitSymbolTable(wasm: *Wasm, binary_bytes: *std.ArrayList(u8), symbol_table: *std.AutoArrayHashMap(SymbolLoc, u32)) !void {
     const writer = binary_bytes.writer();
 
     try leb.writeULEB128(writer, @intFromEnum(types.SubsectionType.WASM_SYMBOL_TABLE));
     const table_offset = binary_bytes.items.len;
 
     var symbol_count: u32 = 0;
     for (wasm.resolved_symbols.keys()) |sym_loc| {
         const symbol = sym_loc.getSymbol(wasm).*;
         if (symbol.tag == .dead) continue; // Do not emit dead symbols
         try symbol_table.putNoClobber(sym_loc, symbol_count);
         symbol_count += 1;
         log.debug("Emit symbol: {}", .{symbol});
         try leb.writeULEB128(writer, @intFromEnum(symbol.tag));
         try leb.writeULEB128(writer, symbol.flags);
 
         const sym_name = if (wasm.export_names.get(sym_loc)) |exp_name| wasm.string_table.get(exp_name) else sym_loc.getName(wasm);
         switch (symbol.tag) {
             .data => {
                 try leb.writeULEB128(writer, @as(u32, @intCast(sym_name.len)));
                 try writer.writeAll(sym_name);
 
                 if (symbol.isDefined()) {
                     try leb.writeULEB128(writer, symbol.index);
                     const atom_index = wasm.symbol_atom.get(sym_loc).?;
                     const atom = wasm.getAtom(atom_index);
                     try leb.writeULEB128(writer, @as(u32, atom.offset));
                     try leb.writeULEB128(writer, @as(u32, atom.size));
                 }
             },
             .section => {
                 try leb.writeULEB128(writer, symbol.index);
             },
             else => {
                 try leb.writeULEB128(writer, symbol.index);
                 if (symbol.isDefined()) {
                     try leb.writeULEB128(writer, @as(u32, @intCast(sym_name.len)));
                     try writer.writeAll(sym_name);
                 }
             },
         }
     }
 
     var buf: [10]u8 = undefined;
     leb.writeUnsignedFixed(5, buf[0..5], @intCast(binary_bytes.items.len - table_offset + 5));
     leb.writeUnsignedFixed(5, buf[5..], symbol_count);
     try binary_bytes.insertSlice(table_offset, &buf);
 }
 
 fn emitSegmentInfo(wasm: *Wasm, binary_bytes: *std.ArrayList(u8)) !void {
     const writer = binary_bytes.writer();
     try leb.writeULEB128(writer, @intFromEnum(types.SubsectionType.WASM_SEGMENT_INFO));
     const segment_offset = binary_bytes.items.len;
 
     try leb.writeULEB128(writer, @as(u32, @intCast(wasm.segment_info.count())));
     for (wasm.segment_info.values()) |segment_info| {
         log.debug("Emit segment: {s} align({d}) flags({b})", .{
             segment_info.name,
             segment_info.alignment,
             segment_info.flags,
         });
         try leb.writeULEB128(writer, @as(u32, @intCast(segment_info.name.len)));
         try writer.writeAll(segment_info.name);
         try leb.writeULEB128(writer, segment_info.alignment.toLog2Units());
         try leb.writeULEB128(writer, segment_info.flags);
     }
 
     var buf: [5]u8 = undefined;
     leb.writeUnsignedFixed(5, &buf, @as(u32, @intCast(binary_bytes.items.len - segment_offset)));
     try binary_bytes.insertSlice(segment_offset, &buf);
 }
 
 pub fn getULEB128Size(uint_value: anytype) u32 {
     const T = @TypeOf(uint_value);
     const U = if (@typeInfo(T).Int.bits < 8) u8 else T;
     var value = @as(U, @intCast(uint_value));
 
     var size: u32 = 0;
     while (value != 0) : (size += 1) {
         value >>= 7;
     }
     return size;
 }
 
 /// For each relocatable section, emits a custom "relocation.<section_name>" section
 fn emitCodeRelocations(
     wasm: *Wasm,
     binary_bytes: *std.ArrayList(u8),
     section_index: u32,
     symbol_table: std.AutoArrayHashMap(SymbolLoc, u32),
 ) !void {
     const code_index = wasm.code_section_index orelse return;
     const writer = binary_bytes.writer();
     const header_offset = try reserveCustomSectionHeader(binary_bytes);
 
     // write custom section information
     const name = "reloc.CODE";
     try leb.writeULEB128(writer, @as(u32, @intCast(name.len)));
     try writer.writeAll(name);
     try leb.writeULEB128(writer, section_index);
     const reloc_start = binary_bytes.items.len;
 
     var count: u32 = 0;
     var atom: *Atom = wasm.getAtomPtr(wasm.atoms.get(code_index).?);
     // for each atom, we calculate the uleb size and append that
     var size_offset: u32 = 5; // account for code section size leb128
     while (true) {
         size_offset += getULEB128Size(atom.size);
         for (atom.relocs.items) |relocation| {
             count += 1;
             const sym_loc: SymbolLoc = .{ .file = atom.file, .index = relocation.index };
             const symbol_index = symbol_table.get(sym_loc).?;
             try leb.writeULEB128(writer, @intFromEnum(relocation.relocation_type));
             const offset = atom.offset + relocation.offset + size_offset;
             try leb.writeULEB128(writer, offset);
             try leb.writeULEB128(writer, symbol_index);
             if (relocation.relocation_type.addendIsPresent()) {
                 try leb.writeILEB128(writer, relocation.addend);
             }
             log.debug("Emit relocation: {}", .{relocation});
         }
         atom = if (atom.prev) |prev| wasm.getAtomPtr(prev) else break;
     }
     if (count == 0) return;
     var buf: [5]u8 = undefined;
     leb.writeUnsignedFixed(5, &buf, count);
     try binary_bytes.insertSlice(reloc_start, &buf);
     const size: u32 = @intCast(binary_bytes.items.len - header_offset - 6);
     try writeCustomSectionHeader(binary_bytes.items, header_offset, size);
 }
 
 fn emitDataRelocations(
     wasm: *Wasm,
     binary_bytes: *std.ArrayList(u8),
     section_index: u32,
     symbol_table: std.AutoArrayHashMap(SymbolLoc, u32),
 ) !void {
     if (wasm.data_segments.count() == 0) return;
     const writer = binary_bytes.writer();
     const header_offset = try reserveCustomSectionHeader(binary_bytes);
 
     // write custom section information
     const name = "reloc.DATA";
     try leb.writeULEB128(writer, @as(u32, @intCast(name.len)));
     try writer.writeAll(name);
     try leb.writeULEB128(writer, section_index);
     const reloc_start = binary_bytes.items.len;
 
     var count: u32 = 0;
     // for each atom, we calculate the uleb size and append that
     var size_offset: u32 = 5; // account for code section size leb128
     for (wasm.data_segments.values()) |segment_index| {
         var atom: *Atom = wasm.getAtomPtr(wasm.atoms.get(segment_index).?);
         while (true) {
             size_offset += getULEB128Size(atom.size);
             for (atom.relocs.items) |relocation| {
                 count += 1;
                 const sym_loc: SymbolLoc = .{ .file = atom.file, .index = relocation.index };
                 const symbol_index = symbol_table.get(sym_loc).?;
                 try leb.writeULEB128(writer, @intFromEnum(relocation.relocation_type));
                 const offset = atom.offset + relocation.offset + size_offset;
                 try leb.writeULEB128(writer, offset);
                 try leb.writeULEB128(writer, symbol_index);
                 if (relocation.relocation_type.addendIsPresent()) {
                     try leb.writeILEB128(writer, relocation.addend);
                 }
                 log.debug("Emit relocation: {}", .{relocation});
             }
             atom = if (atom.prev) |prev| wasm.getAtomPtr(prev) else break;
         }
     }
     if (count == 0) return;
 
     var buf: [5]u8 = undefined;
     leb.writeUnsignedFixed(5, &buf, count);
     try binary_bytes.insertSlice(reloc_start, &buf);
     const size = @as(u32, @intCast(binary_bytes.items.len - header_offset - 6));
     try writeCustomSectionHeader(binary_bytes.items, header_offset, size);
 }
 
 fn hasPassiveInitializationSegments(wasm: *const Wasm) bool {
     const comp = wasm.base.comp;
     const import_memory = comp.config.import_memory;
 
     var it = wasm.data_segments.iterator();
     while (it.next()) |entry| {
         const segment: Segment = wasm.segments.items[entry.value_ptr.*];
         if (segment.needsPassiveInitialization(import_memory, entry.key_ptr.*)) {
             return true;
         }
     }
     return false;
 }
 
 /// Searches for a matching function signature. When no matching signature is found,
 /// a new entry will be made. The value returned is the index of the type within `wasm.func_types`.
 pub fn putOrGetFuncType(wasm: *Wasm, func_type: std.wasm.Type) !u32 {
     if (wasm.getTypeIndex(func_type)) |index| {
         return index;
     }
 
     // functype does not exist.
     const gpa = wasm.base.comp.gpa;
     const index: u32 = @intCast(wasm.func_types.items.len);
     const params = try gpa.dupe(std.wasm.Valtype, func_type.params);
     errdefer gpa.free(params);
     const returns = try gpa.dupe(std.wasm.Valtype, func_type.returns);
     errdefer gpa.free(returns);
     try wasm.func_types.append(gpa, .{
         .params = params,
         .returns = returns,
     });
     return index;
 }
 
 /// For the given `decl_index`, stores the corresponding type representing the function signature.
 /// Asserts declaration has an associated `Atom`.
 /// Returns the index into the list of types.
 pub fn storeDeclType(wasm: *Wasm, decl_index: InternPool.DeclIndex, func_type: std.wasm.Type) !u32 {
     return wasm.zigObjectPtr().?.storeDeclType(wasm.base.comp.gpa, decl_index, func_type);
 }
 
 /// Returns the symbol index of the error name table.
 ///
 /// When the symbol does not yet exist, it will create a new one instead.
 pub fn getErrorTableSymbol(wasm_file: *Wasm) !u32 {
     return wasm_file.zigObjectPtr().?.getErrorTableSymbol(wasm_file);
 }
 
 /// For a given `InternPool.DeclIndex` returns its corresponding `Atom.Index`.
 /// When the index was not found, a new `Atom` will be created, and its index will be returned.
 /// The newly created Atom is empty with default fields as specified by `Atom.empty`.
 pub fn getOrCreateAtomForDecl(wasm_file: *Wasm, decl_index: InternPool.DeclIndex) !Atom.Index {
     return wasm_file.zigObjectPtr().?.getOrCreateAtomForDecl(wasm_file, decl_index);
 }
 
 /// Verifies all resolved symbols and checks whether itself needs to be marked alive,
 /// as well as any of its references.
 fn markReferences(wasm: *Wasm) !void {
     const tracy = trace(@src());
     defer tracy.end();
 
     const do_garbage_collect = wasm.base.gc_sections;
     const comp = wasm.base.comp;
 
     for (wasm.resolved_symbols.keys()) |sym_loc| {
         const sym = sym_loc.getSymbol(wasm);
         if (sym.isExported(comp.config.rdynamic) or sym.isNoStrip() or !do_garbage_collect) {
             try wasm.mark(sym_loc);
             continue;
         }
 
         // Debug sections may require to be parsed and marked when it contains
         // relocations to alive symbols.
         if (sym.tag == .section and comp.config.debug_format != .strip) {
             const obj_file = wasm.file(sym_loc.file) orelse continue; // Incremental debug info is done independently
             _ = try obj_file.parseSymbolIntoAtom(wasm, sym_loc.index);
             sym.mark();
         }
     }
 }
 
 /// Marks a symbol as 'alive' recursively so itself and any references it contains to
 /// other symbols will not be omit from the binary.
 fn mark(wasm: *Wasm, loc: SymbolLoc) !void {
     const symbol = loc.getSymbol(wasm);
     if (symbol.isAlive()) {
         // Symbol is already marked alive, including its references.
         // This means we can skip it so we don't end up marking the same symbols
         // multiple times.
         return;
     }
     symbol.mark();
     if (symbol.isUndefined()) {
         // undefined symbols do not have an associated `Atom` and therefore also
         // do not contain relocations.
         return;
     }
 
     const atom_index = if (wasm.file(loc.file)) |obj_file|
         try obj_file.parseSymbolIntoAtom(wasm, loc.index)
     else
         wasm.symbol_atom.get(loc) orelse return;
 
     const atom = wasm.getAtom(atom_index);
     for (atom.relocs.items) |reloc| {
         const target_loc: SymbolLoc = .{ .index = reloc.index, .file = loc.file };
         try wasm.mark(target_loc.finalLoc(wasm));
     }
 }
 
 fn defaultEntrySymbolName(wasi_exec_model: std.builtin.WasiExecModel) []const u8 {
     return switch (wasi_exec_model) {
         .reactor => "_initialize",
         .command => "_start",
     };
 }