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Date: Thu, 10 Oct 2013 10:31:07 +0200
From: Jakub Jelinek <jakub@...hat.com>
To: Ingo Molnar <mingo@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>,
Oleg Nesterov <oleg@...hat.com>,
Fengguang Wu <fengguang.wu@...el.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Richard Henderson <rth@...ddle.net>
Subject: Re: [PATCH] gcc4: Add 'asm goto' miscompilation quirk
On Thu, Oct 10, 2013 at 10:24:30AM +0200, Ingo Molnar wrote:
> Something like the patch below? (Totally untested and all that.)
>
> Notes:
>
> - If the bug is fixed in 4.8.3 then the version check can be sharpened
> from 99999 to 40803.
The bug is likely going to be fixed already for 4.8.2 (to be released
next week or so).
> - I'd really prefer this quirk versus having to add the extra barrier to
> the label, as it makes the actual usage sites a lot less painful.
Please check how much it bloats the generated code.
Also, for the bitops patch, you probably want an asm_volatile_goto variant.
> --- a/include/linux/compiler-gcc4.h
> +++ b/include/linux/compiler-gcc4.h
> @@ -65,6 +65,19 @@
> #define __visible __attribute__((externally_visible))
> #endif
>
> +/*
> + * GCC 'asm goto' miscompiles certain code sequences:
> + *
> + * http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58670
> + *
> + * Work it around via quirk suggested by Jakub Jelinek.
> + * Not yet fixed, so use the quirk on all compiler versions:
> + */
> +#if GCC_VERSION <= 99999
> +# define asm_goto(x...) do { asm goto(x); asm (""); } while (0)
> +#else
> +# define asm_goto(x...) do { asm goto(x); } while (0)
> +#endif
>
> #ifdef CONFIG_ARCH_USE_BUILTIN_BSWAP
> #if GCC_VERSION >= 40400
Jakub
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