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

[Masahiro Yamada]

On Sun, Jul 28, 2024 at 5:43 AM Brian Gerst <brgerst@xxxxxxxxx> wrote:
>
> On Fri, Jul 26, 2024 at 2:05 PM Nathan Chancellor <nathan@xxxxxxxxxx> 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@xxxxxxxxxxxxxxx
> > 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@xxxxxxxxxx>
> > ---
> > 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@xxxxxxxxx/
>
> Brian Gerst

Judging from the Fixes tags, Nathan meant this patch is
a back-port candidate so that the latest LLVM can be used for stable kernels.

You are making big changes, and do you mean they can be back-ported?



-- 
Best Regards
Masahiro Yamada