From: Nathan Chancellor <natechancellor@gmail.com>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nick Desaulniers <ndesaulniers@google.com>,
linux-kernel@vger.kernel.org, stable@vger.kernel.org,
clang-built-linux@googlegroups.com,
Paul Mackerras <paulus@samba.org>,
linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH] powerpc: Avoid clang warnings around setjmp and longjmp
Date: Wed, 28 Aug 2019 10:53:22 -0700 [thread overview]
Message-ID: <20190828175322.GA121833@archlinux-threadripper> (raw)
In-Reply-To: <878srdv206.fsf@mpe.ellerman.id.au>
On Wed, Aug 28, 2019 at 11:43:53PM +1000, Michael Ellerman wrote:
> Nathan Chancellor <natechancellor@gmail.com> writes:
>
> > Commit aea447141c7e ("powerpc: Disable -Wbuiltin-requires-header when
> > setjmp is used") disabled -Wbuiltin-requires-header because of a warning
> > about the setjmp and longjmp declarations.
> >
> > r367387 in clang added another diagnostic around this, complaining that
> > there is no jmp_buf declaration.
> >
> > In file included from ../arch/powerpc/xmon/xmon.c:47:
> > ../arch/powerpc/include/asm/setjmp.h:10:13: error: declaration of
> > built-in function 'setjmp' requires the declaration of the 'jmp_buf'
> > type, commonly provided in the header <setjmp.h>.
> > [-Werror,-Wincomplete-setjmp-declaration]
> > extern long setjmp(long *);
> > ^
> > ../arch/powerpc/include/asm/setjmp.h:11:13: error: declaration of
> > built-in function 'longjmp' requires the declaration of the 'jmp_buf'
> > type, commonly provided in the header <setjmp.h>.
> > [-Werror,-Wincomplete-setjmp-declaration]
> > extern void longjmp(long *, long);
> > ^
> > 2 errors generated.
> >
> > Take the same approach as the above commit by disabling the warning for
> > the same reason, we provide our own longjmp/setjmp function.
> >
> > Cc: stable@vger.kernel.org # 4.19+
> > Link: https://github.com/ClangBuiltLinux/linux/issues/625
> > Link: https://github.com/llvm/llvm-project/commit/3be25e79477db2d31ac46493d97eca8c20592b07
> > Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
> > ---
> >
> > It may be worth using -fno-builtin-setjmp and -fno-builtin-longjmp
> > instead as it makes it clear to clang that we are not using the builtin
> > longjmp and setjmp functions, which I think is why these warnings are
> > appearing (at least according to the commit that introduced this waring).
> >
> > Sample patch:
> > https://github.com/ClangBuiltLinux/linux/issues/625#issuecomment-519251372
>
> Couldn't we just add those flags to CFLAGS for the whole kernel? Rather
> than making them per-file.
Yes, I don't think this would be unreasonable. Are you referring to the
cc-disable-warning flags or the -fno-builtin flags? I personally think
the -fno-builtin flags convey to clang what the kernel is intending to
do better than disabling the warnings outright.
> I mean there's no kernel code that wants to use clang's builtin
> setjmp/longjmp implementation at all right?
>
> cheers
I did a quick search of the tree and it looks like powerpc and x86/um
are the only architectures that do anything with setjmp/longjmp. x86/um
avoids this by using a define flag to change setjmp to kernel_setjmp:
arch/um/Makefile: -Dlongjmp=kernel_longjmp -Dsetjmp=kernel_setjmp \
Seems like adding those flags should be safe.
Cheers,
Nathan
next prev parent reply other threads:[~2019-08-28 17:55 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-12 2:32 [PATCH] powerpc: Avoid clang warnings around setjmp and longjmp Nathan Chancellor
2019-08-12 5:37 ` Christophe Leroy
2019-08-12 16:55 ` Nathan Chancellor
2019-08-12 17:35 ` Nick Desaulniers
2019-08-27 0:12 ` Nathan Chancellor
2019-08-28 13:43 ` Michael Ellerman
2019-08-28 17:53 ` Nathan Chancellor [this message]
2019-08-28 18:01 ` Nick Desaulniers
2019-08-28 18:45 ` Nathan Chancellor
2019-08-28 22:16 ` Nick Desaulniers
2019-08-29 8:32 ` Segher Boessenkool
2019-08-29 9:59 ` David Laight
2019-09-03 5:55 ` Nathan Chancellor
2019-09-03 19:31 ` Segher Boessenkool
2019-09-04 0:24 ` Nathan Chancellor
2019-09-04 8:16 ` David Laight
2019-09-04 13:01 ` Segher Boessenkool
2019-09-04 23:15 ` Nathan Chancellor
2019-09-10 18:30 ` Michael Ellerman
2019-09-10 18:37 ` Nathan Chancellor
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