Commit 02119362d70bb16ae6ab00124928bde89834c83f | zig

author	Andrew Kelley <andrew@ziglang.org> 2025-10-27 12:11:10-07:00
committer	Andrew Kelley <andrew@ziglang.org> 2025-10-29 06:20:51-07:00
log	02119362d70bb16ae6ab00124928bde89834c83f
tree	8fc933f9cba5df08252b091bc40ef40ad310bfea
parent	6ccb53bff130a473f9d2cc3d0c1ad3a8c6399b2d

wasm linking: handle unreachable call_indirect

The compiler crashed when we tried to call a function pointer for which
the type signature does not match any function body or function import
in the entire wasm executable, because there is no way to create a
reference to a function without it being in the function table or import
table. Solution is to make this instruction lower to unreachable.

1 files changed, 14 insertions(+), 2 deletions(-)

src
- codegen
  - wasm
    Emit.zig

src/codegen/wasm/Emit.zig+14-2

 @@ -188,8 +188,8 @@ pub fn lowerToCode(emit: *Emit) Error!void {
                 .fromInterned(fn_info.return_type),
                 target,
             ).?;
-            code.appendAssumeCapacity(@intFromEnum(std.wasm.Opcode.call_indirect));
             if (is_obj) {
+                code.appendAssumeCapacity(@intFromEnum(std.wasm.Opcode.call_indirect));
                 try wasm.out_relocs.append(gpa, .{
                     .offset = @intCast(code.items.len),
                     .pointee = .{ .type_index = func_ty_index },
 @@ -198,7 +198,19 @@ pub fn lowerToCode(emit: *Emit) Error!void {
                 });
                 code.appendNTimesAssumeCapacity(0, 5);
             } else {
-                const index: Wasm.Flush.FuncTypeIndex = .fromTypeIndex(func_ty_index, &wasm.flush_buffer);
+                const index: Wasm.Flush.FuncTypeIndex = @enumFromInt(wasm.flush_buffer.func_types.getIndex(func_ty_index) orelse {
+                    // In this case we tried to call a function pointer for
+                    // which the type signature does not match any function
+                    // body or function import in the entire wasm executable.
+                    //
+                    // Since there is no way to create a reference to a
+                    // function without it being in the function table or
+                    // import table, this instruction is unreachable.
+                    code.appendAssumeCapacity(@intFromEnum(std.wasm.Opcode.@"unreachable"));
+                    inst += 1;
+                    continue :loop tags[inst];
+                });
+                code.appendAssumeCapacity(@intFromEnum(std.wasm.Opcode.call_indirect));
                 writeUleb128(code, @intFromEnum(index));
             }
             writeUleb128(code, @as(u32, 0)); // table index