Re: [PATCH] gcc4: Add 'asm goto' miscompilation quirk

[Jakub Jelinek <jakub@redhat.com>]

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