From f78380b936de862476ea6b3cc3e8d4ba4562c7fa Mon Sep 17 00:00:00 2001 From: LemonBoy Date: Fri, 16 Oct 2020 12:15:46 +0200 Subject: [PATCH] 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. --- src/stage1/codegen.cpp | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/src/stage1/codegen.cpp b/src/stage1/codegen.cpp index 5e9b84d25a..b8ac867082 100644 --- 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;