zig

commit f78380b936de862476ea6b3cc3e8d4ba4562c7fa (tree)
parent 2a62d4b20be9b99f53367e74434e1971ced78848
Author: LemonBoy <thatlemon@gmail.com>
Date:   Fri, 16 Oct 2020 12:15:46 +0200

stage1: Don't ask LLVM to emit misaligned memcpy

Pay close attention to the RHS type alignment when rendering an
assignment op as it may differ from the LHS pointer one.

This problem was noticed when debugging a CI failure in #6648: due to
sheer luck the misalignment caused a segfault on macos that was also
reproduced locally.

I tried to write a small test case but it turned out to be a daunting
task as I couldn't manage to trigger the problem consistently (and stop
the optimizer from simplifying everything). Patches welcome.

Diffstat:
M
src/stage1/codegen.cpp
 | 
8
+++++---

1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/src/stage1/codegen.cpp b/src/stage1/codegen.cpp
@@ -1645,11 +1645,13 @@ static void gen_assign_raw(CodeGen *g, LLVMValueRef ptr, ZigType *ptr_type,
 
         ZigType *usize = g->builtin_types.entry_usize;
         uint64_t size_bytes = LLVMStoreSizeOfType(g->target_data_ref, get_llvm_type(g, child_type));
-        uint64_t align_bytes = get_ptr_align(g, ptr_type);
+        uint64_t src_align_bytes = get_abi_alignment(g, child_type);
+        uint64_t dest_align_bytes = get_ptr_align(g, ptr_type);
         assert(size_bytes > 0);
-        assert(align_bytes > 0);
+        assert(src_align_bytes > 0);
+        assert(dest_align_bytes > 0);
 
-        ZigLLVMBuildMemCpy(g->builder, dest_ptr, align_bytes, src_ptr, align_bytes,
+        ZigLLVMBuildMemCpy(g->builder, dest_ptr, dest_align_bytes, src_ptr, src_align_bytes,
                 LLVMConstInt(usize->llvm_type, size_bytes, false),
                 ptr_type->data.pointer.is_volatile);
         return;