[PATCH] x86: drop a bogus cc clobber

[PATCH] x86: drop a bogus cc clobber

[Jan Beulich]

With the addition of uses of gcc's condition code outputs (commit
35ccfb7114 "x86, asm: Use CC_SET()/CC_OUT() in <asm/rwsem.h>") there's
now an overlap of outputs and clobbers in __down_write_trylock(). Such
overlaps are generally getting tagged with an error (occasionally even
with an ICE). I can't really tell why plain gcc 6.2 doesn't detect this
(judging by the code it is meant to), while the slightly modified one I
use does. Since condition code clobbers are never necessary on x86
(other than perhaps for documentation purposes, which doesn't really
get done consistently), remove it altogether rather than inventing
something like CC_CLOBBER (to accompany CC_SET/CC_OUT).

Signed-off-by: Jan Beulich <jbeulich@suse.com>

--- a/arch/x86/include/asm/rwsem.h
+++ b/arch/x86/include/asm/rwsem.h
@@ -154,7 +154,7 @@ static inline bool __down_write_trylock(
 		     : "+m" (sem->count), "=&a" (tmp0), "=&r" (tmp1),
 		       CC_OUT(e) (result)
 		     : "er" (RWSEM_ACTIVE_WRITE_BIAS)
-		     : "memory", "cc");
+		     : "memory");
 	return result;
 }
 

[tip:locking/core] locking/rwsem, x86: Drop a bogus cc clobber

[tip-bot for Jan Beulich]

Commit-ID:  c907420fdaec78b17f59a6011cb5f9d6051c6a35
Gitweb:     http://git.kernel.org/tip/c907420fdaec78b17f59a6011cb5f9d6051c6a35
Author:     Jan Beulich <JBeulich@suse.com>
AuthorDate: Mon, 19 Sep 2016 07:27:08 -0600
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 20 Sep 2016 08:26:41 +0200

locking/rwsem, x86: Drop a bogus cc clobber

With the addition of uses of GCC's condition code outputs in commit:

  35ccfb7114 ("x86, asm: Use CC_SET()/CC_OUT() in <asm/rwsem.h>")

... there's now an overlap of outputs and clobbers in __down_write_trylock().

Such overlaps are generally getting tagged with an error (occasionally
even with an ICE). I can't really tell why plain GCC 6.2 doesn't detect
this (judging by the code it is meant to), while the slightly modified
one I use does. Since condition code clobbers are never necessary on x86
(other than perhaps for documentation purposes, which doesn't really
get done consistently), remove it altogether rather than inventing
something like CC_CLOBBER (to accompany CC_SET/CC_OUT).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/57E003CC0200007800110102@prv-mh.provo.novell.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/include/asm/rwsem.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/rwsem.h b/arch/x86/include/asm/rwsem.h
index 8dbc762..3d33a71 100644
--- a/arch/x86/include/asm/rwsem.h
+++ b/arch/x86/include/asm/rwsem.h
@@ -154,7 +154,7 @@ static inline bool __down_write_trylock(struct rw_semaphore *sem)
 		     : "+m" (sem->count), "=&a" (tmp0), "=&r" (tmp1),
 		       CC_OUT(e) (result)
 		     : "er" (RWSEM_ACTIVE_WRITE_BIAS)
-		     : "memory", "cc");
+		     : "memory");
 	return result;
 }