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From: Dmitry Vyukov <dvyukov@google.com>
Date: Mon, 19 Mar 2018 09:43:25 +0300
Message-ID: <CACT4Y+aLqY6wUfRMto_CZxPRSyvPKxK8ucvAmAY-aR_gq8fOAg@mail.gmail.com>
Subject: Re: clang fails on linux-next since commit 8bf705d13039
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Sender: owner-linux-mm@kvack.org
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To: Lukas Bulwahn <lukas.bulwahn@gmail.com>, Nick Desaulniers <ndesaulniers@google.com>, Greg Hackmann <ghackmann@google.com>, Luis Lozano <llozano@google.com>, Matthias Kaehlcke <mka@google.com>, Michael Davidson <md@google.com>, Sami Tolvanen <samitolvanen@google.com>, Paul Lawrence <paullawrence@google.com>
Cc: Ingo Molnar <mingo@kernel.org>, Linux-MM <linux-mm@kvack.org>, kasan-dev <kasan-dev@googlegroups.com>, llvmlinux@lists.linuxfoundation.org, sil2review@lists.osadl.org

On Sat, Mar 17, 2018 at 2:13 PM, Lukas Bulwahn <lukas.bulwahn@gmail.com> wrote:
> Hi Dmitry, hi Ingo,
>
> since commit 8bf705d13039 ("locking/atomic/x86: Switch atomic.h to use atomic-instrumented.h")
> on linux-next (tested and bisected from tag next-20180316), compiling the
> kernel with clang fails with:
>
> In file included from arch/x86/entry/vdso/vdso32/vclock_gettime.c:33:
> In file included from arch/x86/entry/vdso/vdso32/../vclock_gettime.c:15:
> In file included from ./arch/x86/include/asm/vgtod.h:6:
> In file included from ./include/linux/clocksource.h:13:
> In file included from ./include/linux/timex.h:56:
> In file included from ./include/uapi/linux/timex.h:56:
> In file included from ./include/linux/time.h:6:
> In file included from ./include/linux/seqlock.h:36:
> In file included from ./include/linux/spinlock.h:51:
> In file included from ./include/linux/preempt.h:81:
> In file included from ./arch/x86/include/asm/preempt.h:7:
> In file included from ./include/linux/thread_info.h:38:
> In file included from ./arch/x86/include/asm/thread_info.h:53:
> In file included from ./arch/x86/include/asm/cpufeature.h:5:
> In file included from ./arch/x86/include/asm/processor.h:21:
> In file included from ./arch/x86/include/asm/msr.h:67:
> In file included from ./arch/x86/include/asm/atomic.h:279:
> ./include/asm-generic/atomic-instrumented.h:295:10: error: invalid output size for constraint '=a'
>                 return arch_cmpxchg((u64 *)ptr, (u64)old, (u64)new);
>                        ^
> ./arch/x86/include/asm/cmpxchg.h:149:2: note: expanded from macro 'arch_cmpxchg'
>         __cmpxchg(ptr, old, new, sizeof(*(ptr)))
>         ^
> ./arch/x86/include/asm/cmpxchg.h:134:2: note: expanded from macro '__cmpxchg'
>         __raw_cmpxchg((ptr), (old), (new), (size), LOCK_PREFIX)
>         ^
> ./arch/x86/include/asm/cmpxchg.h:95:17: note: expanded from macro '__raw_cmpxchg'
>                              : "=a" (__ret), "+m" (*__ptr)              \
>                                      ^
>
> (... and some more similar and closely related errors)


Thanks for reporting, Lukas.

+more people who are more aware of the current state of clang for kernel.

Are there are known issues in '=a' constraint handling between gcc and
clang? Is there a recommended way to resolve them?

Also, Lukas what's your version of clang? Potentially there are some
fixes for kernel in the very latest versions of clang.