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Merge pull request #14869 from Luukdegram/wasm-linker

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wasm-linker: refactor virtual addresses
This commit is contained in:
Luuk de Gram
2023-03-10 16:48:30 +01:00
committed by GitHub
parent 5a26d1b426 0ee9a52507
commit 904f414e7e
4 changed files with 43 additions and 68 deletions
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82
src/link/Wasm.zig
View File

@@ -468,6 +468,7 @@ fn createSyntheticSymbol(wasm: *Wasm, name: []const u8, tag: Symbol.Tag) !Symbol
.flags = 0,
.tag = tag,
.index = undefined,
.virtual_address = undefined,
});
try wasm.resolved_symbols.putNoClobber(wasm.base.allocator, loc, {});
try wasm.globals.put(wasm.base.allocator, name_offset, loc);
@@ -886,32 +887,12 @@ fn resolveLazySymbols(wasm: *Wasm) !void {
const loc = try wasm.createSyntheticSymbol("__heap_base", .data);
try wasm.discarded.putNoClobber(wasm.base.allocator, kv.value, loc);
_ = wasm.resolved_symbols.swapRemove(loc); // we don't want to emit this symbol, only use it for relocations.
// TODO: Can we use `createAtom` here while also re-using the symbol
// from `createSyntheticSymbol`.
const atom_index = @intCast(Atom.Index, wasm.managed_atoms.items.len);
const atom = try wasm.managed_atoms.addOne(wasm.base.allocator);
atom.* = Atom.empty;
atom.sym_index = loc.index;
atom.alignment = 1;
try wasm.parseAtom(atom_index, .{ .data = .synthetic });
try wasm.symbol_atom.putNoClobber(wasm.base.allocator, loc, atom_index);
}
if (wasm.undefs.fetchSwapRemove("__heap_end")) |kv| {
const loc = try wasm.createSyntheticSymbol("__heap_end", .data);
try wasm.discarded.putNoClobber(wasm.base.allocator, kv.value, loc);
_ = wasm.resolved_symbols.swapRemove(loc);
const atom_index = @intCast(Atom.Index, wasm.managed_atoms.items.len);
const atom = try wasm.managed_atoms.addOne(wasm.base.allocator);
atom.* = Atom.empty;
atom.sym_index = loc.index;
atom.alignment = 1;
try wasm.parseAtom(atom_index, .{ .data = .synthetic });
try wasm.symbol_atom.putNoClobber(wasm.base.allocator, loc, atom_index);
}
}
@@ -1011,6 +992,7 @@ pub fn allocateSymbol(wasm: *Wasm) !u32 {
.flags = @enumToInt(Symbol.Flag.WASM_SYM_BINDING_LOCAL),
.tag = undefined, // will be set after updateDecl
.index = undefined, // will be set after updateDecl
.virtual_address = undefined, // will be set during atom allocation
};
if (wasm.symbols_free_list.popOrNull()) |index| {
wasm.symbols.items[index] = symbol;
@@ -1246,6 +1228,7 @@ pub fn lowerUnnamedConst(wasm: *Wasm, tv: TypedValue, decl_index: Module.Decl.In
.flags = @enumToInt(Symbol.Flag.WASM_SYM_BINDING_LOCAL),
.tag = .data,
.index = undefined,
.virtual_address = undefined,
};
try wasm.resolved_symbols.putNoClobber(wasm.base.allocator, atom.symbolLoc(), {});
@@ -1292,6 +1275,7 @@ pub fn getGlobalSymbol(wasm: *Wasm, name: []const u8) !u32 {
.flags = 0,
.index = undefined, // index to type will be set after merging function symbols
.tag = .function,
.virtual_address = undefined,
};
symbol.setGlobal(true);
symbol.setUndefined(true);
@@ -1610,7 +1594,6 @@ const Kind = union(enum) {
read_only,
uninitialized,
initialized,
synthetic,
},
function: void,
@@ -1621,7 +1604,6 @@ const Kind = union(enum) {
.read_only => return ".rodata.",
.uninitialized => return ".bss.",
.initialized => return ".data.",
.synthetic => return ".synthetic",
}
}
};
@@ -1788,6 +1770,30 @@ fn allocateAtoms(wasm: *Wasm) !void {
}
}
/// 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) {
continue; // only data symbols have virtual addresses
}
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.options.output_mode != .Obj;
const segment_info = if (atom.file) |object_index| blk: {
break :blk wasm.objects.items[object_index].segment_info;
} 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];
symbol.virtual_address = atom.offset + segment.offset;
}
}
fn sortDataSegments(wasm: *Wasm) !void {
var new_mapping: std.StringArrayHashMapUnmanaged(u32) = .{};
try new_mapping.ensureUnusedCapacity(wasm.base.allocator, wasm.data_segments.count());
@@ -1805,7 +1811,6 @@ fn sortDataSegments(wasm: *Wasm) !void {
if (mem.startsWith(u8, name, ".rodata")) return 0;
if (mem.startsWith(u8, name, ".data")) return 1;
if (mem.startsWith(u8, name, ".text")) return 2;
if (mem.startsWith(u8, name, ".synthetic")) return 100; // always at end
return 3;
}
};
@@ -2137,13 +2142,10 @@ fn setupExports(wasm: *Wasm) !void {
break :blk try wasm.string_table.put(wasm.base.allocator, sym_name);
};
const exp: types.Export = if (symbol.tag == .data) exp: {
const atom_index = wasm.symbol_atom.get(sym_loc).?;
const atom = wasm.getAtom(atom_index);
const va = atom.getVA(wasm, symbol);
const global_index = @intCast(u32, wasm.imported_globals_count + wasm.wasm_globals.items.len);
try wasm.wasm_globals.append(wasm.base.allocator, .{
.global_type = .{ .valtype = .i32, .mutable = false },
.init = .{ .i32_const = @intCast(i32, va) },
.init = .{ .i32_const = @intCast(i32, symbol.virtual_address) },
});
break :exp .{
.name = export_name,
@@ -2220,10 +2222,6 @@ fn setupMemory(wasm: *Wasm) !void {
var offset: u32 = @intCast(u32, memory_ptr);
var data_seg_it = wasm.data_segments.iterator();
while (data_seg_it.next()) |entry| {
if (mem.eql(u8, entry.key_ptr.*, ".synthetic")) {
// do not update synthetic segments as they are not part of the output
continue;
}
const segment = &wasm.segments.items[entry.value_ptr.*];
memory_ptr = std.mem.alignForwardGeneric(u64, memory_ptr, segment.alignment);
memory_ptr += segment.size;
@@ -2240,12 +2238,8 @@ fn setupMemory(wasm: *Wasm) !void {
// 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 segment_index = wasm.data_segments.get(".synthetic").?;
const segment = &wasm.segments.items[segment_index];
segment.offset = 0; // for simplicity we store the entire VA into atom's offset.
const atom_index = wasm.symbol_atom.get(loc).?;
const atom = wasm.getAtomPtr(atom_index);
atom.offset = @intCast(u32, mem.alignForwardGeneric(u64, memory_ptr, heap_alignment));
const symbol = loc.getSymbol(wasm);
symbol.virtual_address = @intCast(u32, mem.alignForwardGeneric(u64, memory_ptr, heap_alignment));
}
// Setup the max amount of pages
@@ -2274,12 +2268,8 @@ fn setupMemory(wasm: *Wasm) !void {
log.debug("Total memory pages: {d}", .{wasm.memories.limits.min});
if (wasm.findGlobalSymbol("__heap_end")) |loc| {
const segment_index = wasm.data_segments.get(".synthetic").?;
const segment = &wasm.segments.items[segment_index];
segment.offset = 0;
const atom_index = wasm.symbol_atom.get(loc).?;
const atom = wasm.getAtomPtr(atom_index);
atom.offset = @intCast(u32, memory_ptr);
const symbol = loc.getSymbol(wasm);
symbol.virtual_address = @intCast(u32, memory_ptr);
}
if (wasm.base.options.max_memory) |max_memory| {
@@ -2417,6 +2407,7 @@ pub fn getErrorTableSymbol(wasm: *Wasm) !u32 {
.tag = .data,
.flags = 0,
.index = 0,
.virtual_address = undefined,
};
symbol.setFlag(.WASM_SYM_VISIBILITY_HIDDEN);
@@ -2449,6 +2440,7 @@ fn populateErrorNameTable(wasm: *Wasm) !void {
.tag = .data,
.flags = 0,
.index = 0,
.virtual_address = undefined,
};
names_symbol.setFlag(.WASM_SYM_VISIBILITY_HIDDEN);
@@ -2749,6 +2741,7 @@ fn linkWithZld(wasm: *Wasm, comp: *Compilation, prog_node: *std.Progress.Node) l
try wasm.allocateAtoms();
try wasm.setupMemory();
wasm.allocateVirtualAddresses();
wasm.mapFunctionTable();
try wasm.mergeSections();
try wasm.mergeTypes();
@@ -2867,6 +2860,7 @@ pub fn flushModule(wasm: *Wasm, comp: *Compilation, prog_node: *std.Progress.Nod
try wasm.allocateAtoms();
try wasm.setupMemory();
wasm.allocateVirtualAddresses();
wasm.mapFunctionTable();
try wasm.mergeSections();
try wasm.mergeTypes();
@@ -3460,8 +3454,6 @@ fn emitNameSection(wasm: *Wasm, binary_bytes: *std.ArrayList(u8), arena: std.mem
// bss section is not emitted when this condition holds true, so we also
// do not output a name for it.
if (!wasm.base.options.import_memory and std.mem.eql(u8, key, ".bss")) continue;
// Synthetic segments are not emitted
if (std.mem.eql(u8, key, ".synthetic")) continue;
segments.appendAssumeCapacity(.{ .index = data_segment_index, .name = key });
data_segment_index += 1;
}

24
src/link/Wasm/Atom.zig
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@@ -89,21 +89,6 @@ pub fn getSymbolIndex(atom: Atom) ?u32 {
return atom.sym_index;
}
/// Returns the virtual address of the `Atom`. This is the address starting
/// from the first entry within a section.
pub fn getVA(atom: Atom, wasm: *const Wasm, symbol: *const Symbol) u32 {
if (symbol.tag == .function) return atom.offset;
std.debug.assert(symbol.tag == .data);
const merge_segment = wasm.base.options.output_mode != .Obj;
const segment_info = if (atom.file) |object_index| blk: {
break :blk wasm.objects.items[object_index].segment_info;
} 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];
return segment.offset + atom.offset;
}
/// Resolves the relocations within the atom, writing the new value
/// at the calculated offset.
pub fn resolveRelocs(atom: *Atom, wasm_bin: *const Wasm) void {
@@ -186,14 +171,7 @@ fn relocationValue(atom: Atom, relocation: types.Relocation, wasm_bin: *const Wa
if (symbol.isUndefined()) {
return 0;
}
const target_atom_index = wasm_bin.symbol_atom.get(target_loc) orelse {
// this can only occur during incremental-compilation when a relocation
// still points to a freed decl. It is fine to emit the value 0 here
// as no actual code will point towards it.
return 0;
};
const target_atom = wasm_bin.getAtom(target_atom_index);
const va = @intCast(i32, target_atom.getVA(wasm_bin, symbol));
const va = @intCast(i64, symbol.virtual_address);
return @intCast(u32, va + relocation.addend);
},
.R_WASM_EVENT_INDEX_LEB => return symbol.index,

2
src/link/Wasm/Object.zig
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@@ -270,6 +270,7 @@ fn checkLegacyIndirectFunctionTable(object: *Object) !?Symbol {
.name = table_import.name,
.tag = .table,
.index = 0,
.virtual_address = undefined,
};
table_symbol.setFlag(.WASM_SYM_UNDEFINED);
table_symbol.setFlag(.WASM_SYM_NO_STRIP);
@@ -758,6 +759,7 @@ fn Parser(comptime ReaderType: type) type {
.tag = tag,
.name = undefined,
.index = undefined,
.virtual_address = undefined,
};
switch (tag) {

3
src/link/Wasm/Symbol.zig
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@@ -20,6 +20,9 @@ name: u32,
index: u32,
/// Represents the kind of the symbol, such as a function or global.
tag: Tag,
/// Contains the virtual address of the symbol, relative to the start of its section.
/// This differs from the offset of an `Atom` which is relative to the start of a segment.
virtual_address: u32,
pub const Tag = enum {
function,