From the trace, looking at the source of __raw_cmpxchg(), it immediately reminds me of this clang bug [0] where Clang validates inline asm constraints before running dead code elimination. [0] https://bugs.llvm.org/show_bug.cgi?id=33587 On Sun, Mar 18, 2018 at 11:43 PM Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote: > On Sat, Mar 17, 2018 at 2:13 PM, Lukas Bulwahn <lukas.bulwahn@xxxxxxxxx> 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. -- Thanks, ~Nick Desaulniers
