dwblaikie wrote:
Here's the smallest patch that would put explicit alignment on any packed
structure:
```
diff --git a/clang/lib/CodeGen/CGDebugInfo.cpp
b/clang/lib/CodeGen/CGDebugInfo.cpp
index a072475ba770..bbb13ddd593b 100644
--- a/clang/lib/CodeGen/CGDebugInfo.cpp
+++ b/clang/lib/CodeGen/CGDebugInfo.cpp
@@ -64,7 +64,7 @@ static uint32_t getTypeAlignIfRequired(const Type *Ty, const
ASTContext &Ctx) {
// MaxFieldAlignmentAttr is the attribute added to types
// declared after #pragma pack(n).
if (auto *Decl = Ty->getAsRecordDecl())
- if (Decl->hasAttr<MaxFieldAlignmentAttr>())
+ if (Decl->hasAttr<MaxFieldAlignmentAttr>() || Decl->hasAttr<PackedAttr>())
return TI.Align;
return 0;
```
But I don't think that's the right approach - I think what we should do is
compute the natural alignment of the structure, then compare that to the actual
alignment - and if they differ, we should put an explicit alignment on the
structure. This avoids the risk that other alignment-influencing effects might
be missed (and avoids the case of putting alignment on a structure that, when
packed, just has the same alignment anyway - which is a minor issue, but nice
to get right (eg: packed struct of a single char probably shouldn't have an
explicit alignment - since it's the same as the implicit alignment anyway))
https://github.com/llvm/llvm-project/pull/93809
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