Messages in this thread Patch in this message | | | From | Juergen Gross <> | Subject | [PATCH] x86: modify inline asm constraints in __cmpxchg_double() | Date | Mon, 15 Oct 2018 10:48:02 +0200 |
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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 <jgross@suse.com> --- 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)); \ __ret; \ }) -- 2.16.4
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