Fix improper reuse of global symbols in MachO

Signed-off-by: Jakub Konka <kubkon@jakubkonka.com>

src/Module.zig

@@ -93,7 +93,7 @@ pub const Export = struct {
     /// Byte offset into the file that contains the export directive.
     src: usize,
     /// Represents the position of the export, if any, in the output file.
-    link: link.File.Elf.Export,
+    link: link.File.Export,
     /// The Decl that performs the export. Note that this is *not* the Decl being exported.
     owner_decl: *Decl,
     /// The Decl being exported. Note this is *not* the Decl performing the export.
@@ -1712,7 +1712,10 @@ fn deleteDeclExports(self: *Module, decl: *Decl) void {
             }
         }
         if (self.comp.bin_file.cast(link.File.Elf)) |elf| {
-            elf.deleteExport(exp.link);
+            elf.deleteExport(exp.link.elf);
+        }
+        if (self.comp.bin_file.cast(link.File.MachO)) |macho| {
+            macho.deleteExport(exp.link.macho);
         }
         if (self.failed_exports.remove(exp)) |entry| {
             entry.value.destroy(self.gpa);
@@ -1875,7 +1878,13 @@ pub fn analyzeExport(self: *Module, scope: *Scope, src: usize, borrowed_symbol_n
     new_export.* = .{
         .options = .{ .name = symbol_name },
         .src = src,
-        .link = .{},
+        .link = switch (self.comp.bin_file.tag) {
+            .coff => .{ .coff = {} },
+            .elf => .{ .elf = link.File.Elf.Export{} },
+            .macho => .{ .macho = link.File.MachO.Export{} },
+            .c => .{ .c = {} },
+            .wasm => .{ .wasm = {} },
+        },
         .owner_decl = owner_decl,
         .exported_decl = exported_decl,
         .status = .in_progress,

src/link.zig

@@ -133,6 +133,14 @@ pub const File = struct {
         wasm: ?Wasm.FnData,
     };
 
+    pub const Export = union {
+        elf: Elf.Export,
+        coff: void,
+        macho: MachO.Export,
+        c: void,
+        wasm: void,
+    };
+
     /// For DWARF .debug_info.
     pub const DbgInfoTypeRelocsTable = std.HashMapUnmanaged(Type, DbgInfoTypeReloc, Type.hash, Type.eql, std.hash_map.DefaultMaxLoadPercentage);
 

src/link/Elf.zig

@@ -2588,7 +2588,7 @@ pub fn updateDeclExports(
             },
         };
         const stt_bits: u8 = @truncate(u4, decl_sym.st_info);
-        if (exp.link.sym_index) |i| {
+        if (exp.link.elf.sym_index) |i| {
             const sym = &self.global_symbols.items[i];
             sym.* = .{
                 .st_name = try self.updateString(sym.st_name, exp.options.name),
@@ -2613,7 +2613,7 @@ pub fn updateDeclExports(
                 .st_size = decl_sym.st_size,
             };
 
-            exp.link.sym_index = @intCast(u32, i);
+            exp.link.elf.sym_index = @intCast(u32, i);
         }
     }
 }

src/link/MachO.zig

@@ -115,6 +115,9 @@ local_symbols: std.ArrayListUnmanaged(macho.nlist_64) = .{},
 global_symbols: std.ArrayListUnmanaged(macho.nlist_64) = .{},
 /// Table of all undefined symbols
 undef_symbols: std.ArrayListUnmanaged(macho.nlist_64) = .{},
+
+global_symbol_free_list: std.ArrayListUnmanaged(u32) = .{},
+
 dyld_stub_binder_index: ?u16 = null,
 
 /// Table of symbol names aka the string table.
@@ -178,6 +181,10 @@ pub const TextBlock = struct {
     };
 };
 
+pub const Export = struct {
+    sym_index: ?u32 = null,
+};
+
 pub const SrcFn = struct {
     pub const empty = SrcFn{};
 };
@@ -713,6 +720,7 @@ pub fn deinit(self: *MachO) void {
     self.string_table.deinit(self.base.allocator);
     self.undef_symbols.deinit(self.base.allocator);
     self.global_symbols.deinit(self.base.allocator);
+    self.global_symbol_free_list.deinit(self.base.allocator);
     self.local_symbols.deinit(self.base.allocator);
     self.sections.deinit(self.base.allocator);
     self.load_commands.deinit(self.base.allocator);
@@ -837,7 +845,7 @@ pub fn updateDeclExports(
             },
         };
         const n_type = decl_sym.n_type | macho.N_EXT;
-        if (exp.link.sym_index) |i| {
+        if (exp.link.macho.sym_index) |i| {
             const sym = &self.global_symbols.items[i];
             sym.* = .{
                 .n_strx = try self.updateString(sym.n_strx, exp.options.name),
@@ -848,8 +856,10 @@ pub fn updateDeclExports(
             };
         } else {
             const name_str_index = try self.makeString(exp.options.name);
-            _ = self.global_symbols.addOneAssumeCapacity();
-            const i = self.global_symbols.items.len - 1;
+            const i = if (self.global_symbol_free_list.popOrNull()) |i| i else blk: {
+                _ = self.global_symbols.addOneAssumeCapacity();
+                break :blk self.global_symbols.items.len - 1;
+            };
             self.global_symbols.items[i] = .{
                 .n_strx = name_str_index,
                 .n_type = n_type,
@@ -858,11 +868,17 @@ pub fn updateDeclExports(
                 .n_value = decl_sym.n_value,
             };
 
-            exp.link.sym_index = @intCast(u32, i);
+            exp.link.macho.sym_index = @intCast(u32, i);
         }
     }
 }
 
+pub fn deleteExport(self: *MachO, exp: Export) void {
+    const sym_index = exp.sym_index orelse return;
+    self.global_symbol_free_list.append(self.base.allocator, sym_index) catch {};
+    self.global_symbols.items[sym_index].n_type = 0;
+}
+
 pub fn freeDecl(self: *MachO, decl: *Module.Decl) void {}
 
 pub fn getDeclVAddr(self: *MachO, decl: *const Module.Decl) u64 {