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Wed, 28 Aug 2019 11:45:31 -0700 (PDT) Date: Wed, 28 Aug 2019 11:45:29 -0700 From: Nathan Chancellor To: Nick Desaulniers Cc: Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , linuxppc-dev , LKML , clang-built-linux , "# 3.4.x" Subject: Re: [PATCH] powerpc: Avoid clang warnings around setjmp and longjmp Message-ID: <20190828184529.GC127646@archlinux-threadripper> References: <20190812023214.107817-1-natechancellor@gmail.com> <878srdv206.fsf@mpe.ellerman.id.au> <20190828175322.GA121833@archlinux-threadripper> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.12.1 (2019-06-15) Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Wed, Aug 28, 2019 at 11:01:14AM -0700, Nick Desaulniers wrote: > On Wed, Aug 28, 2019 at 10:53 AM Nathan Chancellor > wrote: > > > > On Wed, Aug 28, 2019 at 11:43:53PM +1000, Michael Ellerman wrote: > > > Nathan Chancellor 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 . > > > > [-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 . > > > > [-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 > > > > --- > > > > > > > > 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. > > The `-f` family of flags have dire implications for codegen, I'd > really prefer we think long and hard before adding/removing them to > suppress warnings. I don't think it's a solution for this particular > problem. I am fine with whatever approach gets this warning fixed to the maintainer's satisfaction... However, I think that -fno-builtin-* would be appropriate here because we are providing our own setjmp implementation, meaning clang should not be trying to do anything with the builtin implementation like building a declaration for it. Cheers, Nathan