From 1b1921f0e26b9cb8ac78003c9061acac2da5e7ab Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Sat, 8 Aug 2020 01:00:29 -0700
Subject: [PATCH] stage1: deal with WebAssembly not supporting @returnAddress()

This makes `@returnAddress()` return 0 for WebAssembly (when not using
the Emscripten OS) and avoids trying to capture stack traces for the
general purpose allocator on that target.
---
 lib/std/heap.zig                           | 11 +++++++++--
 lib/std/heap/general_purpose_allocator.zig |  5 ++++-
 src/codegen.cpp                            |  6 ++++++
 3 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/lib/std/heap.zig b/lib/std/heap.zig
index 88f27fad49..0c9dbca369 100644
--- a/lib/std/heap.zig
+++ b/lib/std/heap.zig
@@ -37,7 +37,7 @@ var c_allocator_state = Allocator{
     .resizeFn = cResize,
 };
 
-fn cAlloc(self: *Allocator, len: usize, ptr_align: u29, len_align: u29) Allocator.Error![]u8 {
+fn cAlloc(self: *Allocator, len: usize, ptr_align: u29, len_align: u29, ret_addr: usize) Allocator.Error![]u8 {
     assert(ptr_align <= @alignOf(c_longdouble));
     const ptr = @ptrCast([*]u8, c.malloc(len) orelse return error.OutOfMemory);
     if (len_align == 0) {
@@ -54,7 +54,14 @@ fn cAlloc(self: *Allocator, len: usize, ptr_align: u29, len_align: u29) Allocato
     return ptr[0..mem.alignBackwardAnyAlign(full_len, len_align)];
 }
 
-fn cResize(self: *Allocator, buf: []u8, old_align: u29, new_len: usize, len_align: u29) Allocator.Error!usize {
+fn cResize(
+    self: *Allocator,
+    buf: []u8,
+    old_align: u29,
+    new_len: usize,
+    len_align: u29,
+    ret_addr: usize,
+) Allocator.Error!usize {
     if (new_len == 0) {
         c.free(buf.ptr);
         return 0;
diff --git a/lib/std/heap/general_purpose_allocator.zig b/lib/std/heap/general_purpose_allocator.zig
index 98f029579c..5369560356 100644
--- a/lib/std/heap/general_purpose_allocator.zig
+++ b/lib/std/heap/general_purpose_allocator.zig
@@ -102,9 +102,12 @@ const StackTrace = std.builtin.StackTrace;
 /// Integer type for pointing to slots in a small allocation
 const SlotIndex = std.meta.Int(false, math.log2(page_size) + 1);
 
+// WebAssembly doesn't support stack tracing yet.
+const default_stack_trace_frames: usize = if (std.Target.current.cpu.arch.isWasm()) 0 else 4;
+
 pub const Config = struct {
     /// Number of stack frames to capture.
-    stack_trace_frames: usize = if (std.debug.runtime_safety) @as(usize, 4) else @as(usize, 0),
+    stack_trace_frames: usize = if (std.debug.runtime_safety) default_stack_trace_frames else @as(usize, 0),
 
     /// If true, the allocator will have two fields:
     ///  * `total_requested_bytes` which tracks the total allocated bytes of memory requested.
diff --git a/src/codegen.cpp b/src/codegen.cpp
index 023c94f245..6941eae466 100644
--- a/src/codegen.cpp
+++ b/src/codegen.cpp
@@ -5886,6 +5886,12 @@ static LLVMValueRef ir_render_breakpoint(CodeGen *g, IrExecutableGen *executable
 static LLVMValueRef ir_render_return_address(CodeGen *g, IrExecutableGen *executable,
         IrInstGenReturnAddress *instruction)
 {
+    if (target_is_wasm(g->zig_target) && g->zig_target->os != OsEmscripten) {
+        // I got this error from LLVM 10:
+        // "Non-Emscripten WebAssembly hasn't implemented __builtin_return_address"
+        return LLVMConstNull(get_llvm_type(g, instruction->base.value->type));
+    }
+
     LLVMValueRef zero = LLVMConstNull(g->builtin_types.entry_i32->llvm_type);
     LLVMValueRef ptr_val = LLVMBuildCall(g->builder, get_return_address_fn_val(g), &zero, 1, "");
     return LLVMBuildPtrToInt(g->builder, ptr_val, g->builtin_types.entry_usize->llvm_type, "");