From 5aec88fa4102e87295bf60971209d114c6ae6733 Mon Sep 17 00:00:00 2001
From: Luuk de Gram <luuk@degram.dev>
Date: Mon, 5 Feb 2024 17:17:07 +0100
Subject: [PATCH] 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.
---
 src/arch/wasm/Emit.zig      | 14 +++++++++++++-
 src/link/Wasm.zig           |  4 +++-
 src/link/Wasm/ZigObject.zig | 10 ++++++++--
 3 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/src/arch/wasm/Emit.zig b/src/arch/wasm/Emit.zig
index 31c15ce0ef..ded960daf1 100644
--- a/src/arch/wasm/Emit.zig
+++ b/src/arch/wasm/Emit.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
 }
 
diff --git a/src/link/Wasm.zig b/src/link/Wasm.zig
index 26dd8b47b6..5f4277dfdd 100644
--- a/src/link/Wasm.zig
+++ b/src/link/Wasm.zig
@@ -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);
         }
 
diff --git a/src/link/Wasm/ZigObject.zig b/src/link/Wasm/ZigObject.zig
index ae5252cdd4..e73bd466cc 100644
--- a/src/link/Wasm/ZigObject.zig
+++ b/src/link/Wasm/ZigObject.zig
@@ -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 => {},