Subject: [PATCH v2] ARM: teach __asmeq that r11 == fp and r12 == ip

From: [email-masked] (Alex Elder)
Date: Thu, 29 Jan 2015 06:44:30 -0600

On 01/29/2015 03:44 AM, Ard Biesheuvel wrote:
> The __asmeq macro is used inside inline asm statements to ensure that
> register asm variables that explicitly specify a register are mapped
> correctly onto those registers when used in inline asm input and output
> constraints. However, the string based matching fails to take into account
> that 'fp' is often referred to as 'r11' and 'ip' is often referred to as
> 'r12', (e.g., by clang), causing false negatives.
> 
> Fix this by making __asmeq consider the ("fp","r11"), ("r11","fp"),
> ("ip","r12") and ("r12","ip") cases specifically.
> 
> Signed-off-by: Ard Biesheuvel <[email-masked]>

I'm satisfied.  Kind of awkward, but it does what's needed,
and solves the general problem rather than a specific instance
of it in "bcm_kona_smc.c".

I tested it in my environment with "r12" and "ip" used in
all combinations and can confirm they all work as desired.

Thanks for doing this Ard.

Reviewed-by: Alex Elder <[email-masked]>

> ---
> v2:
> Added r11 but not r10, as the latter is only referred to as 'sl' in
> objdump output, but GCC emitted inline asm substitutes the references
> with 'r10' instead. sp/lr/pc are unambiguous between GCC and clang.
> 
> Primary purpose of this patch is to fix the incompatibility between clang
> and GCC, but the side effect is that it relaxes the requirement imposed on
> the programmer to refer to a register by the same name as the compiler does.
> If that is seen as a substantial upside by some, we could indeed still decide
> to add r10, r13, r14 and r15 (for which no such incompatibility exists) as well.
> However, those are not currently used in __asmeq invocations anywhere under
> arch/arm
> 
>  arch/arm/include/asm/compiler.h | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/include/asm/compiler.h b/arch/arm/include/asm/compiler.h
> index 8155db2f7fa1..29fe85e59439 100644
> --- a/arch/arm/include/asm/compiler.h
> +++ b/arch/arm/include/asm/compiler.h
> @@ -8,8 +8,21 @@
>   * This string is meant to be concatenated with the inline asm string and
>   * will cause compilation to stop on mismatch.
>   * (for details, see gcc PR 15089)
> + * For compatibility with clang, we have to specifically take the equivalence
> + * of 'r11' <-> 'fp' and 'r12' <-> 'ip' into account as well.
>   */
> -#define __asmeq(x, y)  ".ifnc " x "," y " ; .err ; .endif\n\t"
> +#define __asmeq(x, y)				\
> +	".ifnc " x "," y "; "			\
> +	  ".ifnc " x y ",fpr11; " 		\
> +	    ".ifnc " x y ",r11fp; "		\
> +	      ".ifnc " x y ",ipr12; " 		\
> +	        ".ifnc " x y ",r12ip; "		\
> +	          ".err; "			\
> +	        ".endif; "			\
> +	      ".endif; "			\
> +	    ".endif; "				\
> +	  ".endif; "				\
> +	".endif\n\t"
>  
>  
>  #endif /* __ASM_ARM_COMPILER_H */
>