Re: [PATCH] hardening: Require clang 20.1.0 for __counted_by

[Alexander Lobakin <aleksander.lobakin@intel.com>]

From: Nathan Chancellor <nathan@kernel.org>
Date: Thu, 07 Aug 2025 14:36:28 -0700

> After an innocuous change in -next that modified a structure that
> contains __counted_by, clang-19 start crashing when building certain
> files in drivers/gpu/drm/xe. When assertions are enabled, the more
> descriptive failure is:
> 
>   clang: clang/lib/AST/RecordLayoutBuilder.cpp:3335: const ASTRecordLayout &clang::ASTContext::getASTRecordLayout(const RecordDecl *) const: Assertion `D && "Cannot get layout of forward declarations!"' failed.
> 
> According to a reverse bisect, a tangential change to the LLVM IR
> generation phase of clang during the LLVM 20 development cycle [1]
> resolves this problem. Bump the version of clang that enables
> CONFIG_CC_HAS_COUNTED_BY to 20.1.0 to ensure that this issue cannot be
> hit.

Any chance for this to go to the next 19.x (if it's planned at all)?
I always use the latest HEAD from llvm-project, but 19 is still widely
used across distros etc =\

> 
> Link: https://github.com/llvm/llvm-project/commit/160fb1121cdf703c3ef5e61fb26c5659eb581489 [1]
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> ---
> Should this be marked for stable? If this makes 6.17 final, I think we
> are fine for mainline and newer but I wonder if a patch that adds
> __counted_by to a structure would ever be backported and expose this
> problem there.

Thanks,
Olek