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stage1: Don't ask LLVM to emit misaligned memcpy

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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.
This commit is contained in:
LemonBoy 2020-10-16 12:15:46 +02:00 committed by Andrew Kelley
parent 2a62d4b20b
commit f78380b936
1 changed files with 5 additions and 3 deletions
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8
src/stage1/codegen.cpp
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@ -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;