Commit `5aec88fa41`

Luuk de Gram <luuk@degram.dev>

2024-02-05 17:17:07

wasm: correctly generate relocations for type index

Previously we could directly write the type index because we used the index that was known in the final binary. However, as we now process the Zig module as its own relocatable object file, we must ensure to generate a relocation for type indexes. This also ensures that we can later link the relocatable object file as a standalone also. This also fixes generating indirect function table entries for ZigObject as it now correctly points to the relocation symbol index rather than the symbol index that owns the relocation.

master

1 parent 5a0f2af

Changed files (3)

src

arch

wasm

Emit.zig

link

Wasm

ZigObject.zig

Wasm.zig

@@ -385,7 +385,19 @@ fn emitCallIndirect(emit: *Emit, inst: Mir.Inst.Index) !void {
     try emit.code.append(std.wasm.opcode(.call_indirect));
     // NOTE: If we remove unused function types in the future for incremental
     // linking, we must also emit a relocation for this `type_index`
-    try leb128.writeULEB128(emit.code.writer(), type_index);
+    const call_offset = emit.offset();
+    var buf: [5]u8 = undefined;
+    leb128.writeUnsignedFixed(5, &buf, type_index);
+    try emit.code.appendSlice(&buf);
+    if (type_index != 0) {
+        const atom_index = emit.bin_file.zigObjectPtr().?.decls_map.get(emit.decl_index).?.atom;
+        const atom = emit.bin_file.getAtomPtr(atom_index);
+        try atom.relocs.append(emit.bin_file.base.comp.gpa, .{
+            .offset = call_offset,
+            .index = type_index,
+            .relocation_type = .R_WASM_TYPE_INDEX_LEB,
+        });
+    }
     try leb128.writeULEB128(emit.code.writer(), @as(u32, 0)); // TODO: Emit relocation for table index
 }

@@ -1137,14 +1137,20 @@ pub fn parseSymbolIntoAtom(zig_object: *ZigObject, wasm_file: *Wasm, index: u32)
             .R_WASM_TABLE_INDEX_SLEB,
             .R_WASM_TABLE_INDEX_SLEB64,
             => {
-                try wasm_file.function_table.put(gpa, loc, 0);
+                try wasm_file.function_table.put(gpa, .{
+                    .file = zig_object.index,
+                    .index = reloc.index,
+                }, 0);
             },
             .R_WASM_GLOBAL_INDEX_I32,
             .R_WASM_GLOBAL_INDEX_LEB,
             => {
                 const sym = zig_object.symbol(reloc.index);
                 if (sym.tag != .global) {
-                    try wasm_file.got_symbols.append(gpa, loc);
+                    try wasm_file.got_symbols.append(gpa, .{
+                        .file = zig_object.index,
+                        .index = reloc.index,
+                    });
                 }
             },
             else => {},

@@ -3057,7 +3057,9 @@ fn writeToFile(
         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);
+            const sym = symbol_loc_ptr.getSymbol(wasm);
+            std.debug.assert(sym.isAlive());
+            std.debug.assert(sym.index < wasm.functions.count() + wasm.imported_functions_count);
             try leb.writeULEB128(binary_writer, sym.index);
         }

Commit 5aec88fa41

Commit `5aec88fa41`