linux-hardening - Re: [PATCH] hardening: Require clang 20.1.0 for __counted

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Message-ID: <adb1b558-124c-4f7f-b193-bf44a6132fa2@intel.com>
Date: Tue, 12 Aug 2025 18:28:29 +0200
From: Alexander Lobakin <aleksander.lobakin@...el.com>
To: Nathan Chancellor <nathan@...nel.org>
CC: Kees Cook <kees@...nel.org>, "Gustavo A. R. Silva"
	<gustavoars@...nel.org>, Bill Wendling <morbo@...gle.com>, Justin Stitt
	<justinstitt@...gle.com>, <linux-hardening@...r.kernel.org>,
	<llvm@...ts.linux.dev>, <patches@...ts.linux.dev>
Subject: Re: [PATCH] hardening: Require clang 20.1.0 for __counted_by

From: Nathan Chancellor <nathan@...nel.org>
Date: Mon, 11 Aug 2025 14:09:06 -0700

> On Mon, Aug 11, 2025 at 04:21:32PM +0200, Alexander Lobakin wrote:
>> From: Nathan Chancellor <nathan@...nel.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 =\
> 
> Unfortunately not, LLVM does not maintain more than one branch at a
> time, so LLVM 19 has been unsupported since LLVM 20.1.0-rc1 was
> released back in February :/

Aaah okay, I didn't know that, thanks!

BTW 21-rc1 was released roughly a month ago, does this mean that 20.x is
already unsupported?

> Cheers,
> Nathan

Olek