linux-kernel - Re: [PATCH] kbuild: Fix '-S -c' in x86 stack protector scripts

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Message-ID: <CAMzpN2hRVzWOF5YDvE8pPKfogdcuou8REsY+uXzkdORnFn=buQ@mail.gmail.com>
Date: Sat, 27 Jul 2024 16:43:00 -0400
From: Brian Gerst <brgerst@...il.com>
To: Nathan Chancellor <nathan@...nel.org>
Cc: masahiroy@...nel.org, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, 
	dave.hansen@...ux.intel.com, x86@...nel.org, nicolas@...sle.eu, 
	maskray@...gle.com, morbo@...gle.com, justinstitt@...gle.com, kees@...nel.org, 
	linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org, 
	llvm@...ts.linux.dev, patches@...ts.linux.dev, stable@...r.kernel.org
Subject: Re: [PATCH] kbuild: Fix '-S -c' in x86 stack protector scripts

On Fri, Jul 26, 2024 at 2:05 PM Nathan Chancellor <nathan@...nel.org> wrote:
>
> After a recent change in clang to stop consuming all instances of '-S'
> and '-c' [1], the stack protector scripts break due to the kernel's use
> of -Werror=unused-command-line-argument to catch cases where flags are
> not being properly consumed by the compiler driver:
>
>   $ echo | clang -o - -x c - -S -c -Werror=unused-command-line-argument
>   clang: error: argument unused during compilation: '-c' [-Werror,-Wunused-command-line-argument]
>
> This results in CONFIG_STACKPROTECTOR getting disabled because
> CONFIG_CC_HAS_SANE_STACKPROTECTOR is no longer set.
>
> '-c' and '-S' both instruct the compiler to stop at different stages of
> the pipeline ('-S' after compiling, '-c' after assembling), so having
> them present together in the same command makes little sense. In this
> case, the test wants to stop before assembling because it is looking at
> the textual assembly output of the compiler for either '%fs' or '%gs',
> so remove '-c' from the list of arguments to resolve the error.
>
> All versions of GCC continue to work after this change, along with
> versions of clang that do or do not contain the change mentioned above.
>
> Cc: stable@...r.kernel.org
> Fixes: 4f7fd4d7a791 ("[PATCH] Add the -fstack-protector option to the CFLAGS")
> Fixes: 60a5317ff0f4 ("x86: implement x86_32 stack protector")
> Link: https://github.com/llvm/llvm-project/commit/6461e537815f7fa68cef06842505353cf5600e9c [1]
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> ---
> I think this could go via either -tip or Kbuild?
>
> Perhaps this is an issue in the clang commit mentioned in the message
> above since it deviates from GCC (Fangrui is on CC here) but I think the
> combination of these options is a little dubious to begin with, hence
> this change.

As part of my stack protector cleanup series, I found that these
scripts can simply be removed.  I can repost those patches as a
standalone cleanup.

https://lore.kernel.org/lkml/20240322165233.71698-1-brgerst@gmail.com/

Brian Gerst