linux-kernel - [PATCH v2] compiler/gcc4: make quirk for asm_volatile

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Message-Id: <1392274867-15236-1-git-send-email-steven@uplinklabs.net>
Date:	Wed, 12 Feb 2014 23:01:07 -0800
From:	Steven Noonan <steven@...inklabs.net>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:	Steven Noonan <steven@...inklabs.net>, Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	stable@...r.kernel.org
Subject: [PATCH v2] compiler/gcc4: make quirk for asm_volatile_goto unconditional

I started noticing problems with KVM guest destruction on Linux 3.12+, where
guest memory wasn't being cleaned up. I bisected it down to the commit
introducing the new 'asm goto'-based atomics, and found this quirk was later
applied to those.

Unfortunately, even with GCC 4.8.2 (which ostensibly fixed the known 'asm goto'
bug) I am still getting some kind of miscompilation. If I enable the
asm_volatile_goto quirk for my compiler, KVM guests are destroyed correctly and
the memory is cleaned up.

[1] http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58670
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: stable@...r.kernel.org
Signed-off-by: Steven Noonan <steven@...inklabs.net>
---

v2: Adding stable@...r.kernel.org to Cc.

 include/linux/compiler-gcc4.h | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/include/linux/compiler-gcc4.h b/include/linux/compiler-gcc4.h
index ded4299..2507fd2 100644
--- a/include/linux/compiler-gcc4.h
+++ b/include/linux/compiler-gcc4.h
@@ -75,11 +75,7 @@
  *
  * (asm goto is automatically volatile - the naming reflects this.)
  */
-#if GCC_VERSION <= 40801
-# define asm_volatile_goto(x...)	do { asm goto(x); asm (""); } while (0)
-#else
-# define asm_volatile_goto(x...)	do { asm goto(x); } while (0)
-#endif
+#define asm_volatile_goto(x...)	do { asm goto(x); asm (""); } while (0)
 
 #ifdef CONFIG_ARCH_USE_BUILTIN_BSWAP
 #if GCC_VERSION >= 40400
-- 
1.8.5.4

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