Re: clang fails on linux-next since commit 8bf705d13039

[Dmitry Vyukov <dvyukov@google.com>]

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.