Re: [Qemu-devel] [PATCH 5/5] tcg-arm: Use AT_PLATFORM to detect the host ISA

[Claudio Fontana]

Richard wrote (eons ago):
> With this we can generate armv7 insns even when the OS compiles for a
> lower common denominator.  The macros are arranged so that when we do
> compile for a given ISA, all of the runtime checks for that ISA are
> optimized away.
> 
> Signed-off-by: Richard Henderson <address@hidden>
> ---
>  tcg/arm/tcg-target.c | 22 +++++++++++++++++-----
>  1 file changed, 17 insertions(+), 5 deletions(-)
> 
> diff --git a/tcg/arm/tcg-target.c b/tcg/arm/tcg-target.c
> index 202f1fc..243dedd 100644
> --- a/tcg/arm/tcg-target.c
> +++ b/tcg/arm/tcg-target.c
> @@ -41,9 +41,11 @@
>  # endif
>  #endif
>  
> -#define use_armv5_instructions  (__ARM_ARCH >= 5)
> -#define use_armv6_instructions  (__ARM_ARCH >= 6)
> -#define use_armv7_instructions  (__ARM_ARCH >= 7)
> +static int arm_arch = __ARM_ARCH;
> +
> +#define use_armv5_instructions  (__ARM_ARCH >= 5 || arm_arch >= 5)
> +#define use_armv6_instructions  (__ARM_ARCH >= 6 || arm_arch >= 6)
> +#define use_armv7_instructions  (__ARM_ARCH >= 7 || arm_arch >= 7)
>  
>  #ifndef use_idiv_instructions
>  bool use_idiv_instructions;
> @@ -2036,12 +2038,22 @@ static const TCGTargetOpDef arm_op_defs[] = {
>  
>  static void tcg_target_init(TCGContext *s)
>  {
> -#if defined(CONFIG_GETAUXVAL) && !defined(use_idiv_instructions)
> +#if defined(CONFIG_GETAUXVAL)
> +    /* Only probe for the platform and capabilities if we havn't already
> +       determined maximum values at compile time.  */
> +# if !defined(use_idiv_instructions)
>      {
>          unsigned long hwcap = getauxval(AT_HWCAP);
>          use_idiv_instructions = hwcap & (HWCAP_ARM_IDIVA | HWCAP_ARM_IDIVT);
>      }
> -#endif
> +# endif
> +    if (__ARM_ARCH < 7) {
> +        const char *pl = (const char *)getauxval(AT_PLATFORM);
> +        if (pl != NULL && pl[0] == 'v' && pl[1] >= '4' && pl[1] <= '9') {
> +            arm_arch = pl[1] - '0';
> +        }
> +    }
> +#endif /* GETAUXVAL */
>  
>  #if !defined(CONFIG_USER_ONLY)
>      /* fail safe */
> -- 
> 1.8.1.4
> 

this also fails to apply at the moment because of the removal of the 'fail 
safe' thing.

Claudio