On 16/10/2018 08:25, Ingo Molnar wrote: > > * Juergen Gross <[email protected]> wrote: > >> Some gcc versions seem to have problems with the constraints in >> __cmpxchg_double() as they suddenly issue a build error when random >> parts of sources calling __cmpxchg_double() are modified, like e.g. >> slub.c. This has been observed on Debian systems only so far. >> >> Using "0" instead of "a" in the input constraints has the same >> semantics while avoiding that build error. >> >> Signed-off-by: Juergen Gross <[email protected]> >> --- >> I should note that I have observed gcc hangs instead sometimes. Not >> taking any patches modifying users of __cmpxchg_double() due to a gcc >> bug which seems to be distro-specific is a bad move IMO. >> >> I'd rather make it clear from build behavior that this is a bug in gcc >> by letting the build hang instead of throwing error warnings not in any >> way related to changes in the code. >> >> The gcc bug is filed under: >> >> https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=908154 >> --- >> arch/x86/include/asm/cmpxchg.h | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/arch/x86/include/asm/cmpxchg.h b/arch/x86/include/asm/cmpxchg.h >> index a55d79b233d3..b3b4d61a8969 100644 >> --- a/arch/x86/include/asm/cmpxchg.h >> +++ b/arch/x86/include/asm/cmpxchg.h >> @@ -245,7 +245,7 @@ extern void __add_wrong_size(void) >> asm volatile(pfx "cmpxchg%c4b %2; sete %0" \ >> : "=a" (__ret), "+d" (__old2), \ >> "+m" (*(p1)), "+m" (*(p2)) \ >> - : "i" (2 * sizeof(long)), "a" (__old1), \ >> + : "i" (2 * sizeof(long)), "0" (__old1), \ >> "b" (__new1), "c" (__new2)); \ > > This got changed to +a in -tip: > > c808c09b527c: x86/asm: Use CC_SET()/CC_OUT() in __cmpxchg_double() > > Mind sending a patch on top of -tip?
No, I think you can drop my patch. c808c09b527c: x86/asm: Use CC_SET()/CC_OUT() in __cmpxchg_double() has the same effect as my patch: the build failure is replaced by gcc hanging instead in the critical configuration. Juergen
