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

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Date:	Thu, 13 Feb 2014 07:48:26 +0100
From:	Mike Galbraith <bitbucket@...ine.de>
To:	Steven Noonan <steven@...inklabs.net>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] compiler/gcc4: make quirk for asm_volatile_goto
 unconditional

On Wed, 2014-02-12 at 20:53 -0800, Steven Noonan wrote: 
> 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 v3.12+ ?

> Signed-off-by: Steven Noonan <steven@...inklabs.net>
> ---
>  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


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