Re: [Qemu-devel] [PATCH v2 25/27] tcg-ppc64: Use getauxval for ISA detection

[Aurelien Jarno <aurelien@aurel32.net>]

On Mon, Mar 04, 2013 at 04:33:08PM -0800, Richard Henderson wrote:
> Glibc 2.16 includes an easy way to get feature bits previously
> buried in /proc or the program startup auxiliary vector.  Use it.
> 
> Signed-off-by: Richard Henderson <rth@twiddle.net>
> ---
>  configure              | 18 ++++++++++++++++++
>  tcg/ppc64/tcg-target.c | 20 +++++++++++++++++++-
>  2 files changed, 37 insertions(+), 1 deletion(-)
> 
> diff --git a/configure b/configure
> index 19738ac..c876099 100755
> --- a/configure
> +++ b/configure
> @@ -3214,6 +3214,20 @@ if compile_prog "" "" ; then
>      int128=yes
>  fi
>  
> +########################################
> +# check if getauxval is available.
> +
> +getauxval=no
> +cat > $TMPC << EOF
> +#include <sys/auxv.h>
> +int main(void) {
> +  return getauxval(AT_HWCAP) == 0;
> +}
> +EOF
> +if compile_prog "" "" ; then
> +    getauxval=yes
> +fi
> +
>  ##########################################
>  # End of CC checks
>  # After here, no more $cc or $ld runs
> @@ -3767,6 +3781,10 @@ if test "$int128" = "yes" ; then
>    echo "CONFIG_INT128=y" >> $config_host_mak
>  fi
>  
> +if test "$getauxval" = "yes" ; then
> +  echo "CONFIG_GETAUXVAL=y" >> $config_host_mak
> +fi
> +
>  if test "$glusterfs" = "yes" ; then
>    echo "CONFIG_GLUSTERFS=y" >> $config_host_mak
>  fi
> diff --git a/tcg/ppc64/tcg-target.c b/tcg/ppc64/tcg-target.c
> index 2acccf6..826726d 100644
> --- a/tcg/ppc64/tcg-target.c
> +++ b/tcg/ppc64/tcg-target.c
> @@ -44,8 +44,16 @@ static uint8_t *tb_ret_addr;
>  #define GUEST_BASE 0
>  #endif
>  
> +#ifdef CONFIG_GETAUXVAL
> +#include <sys/auxv.h>
> +static bool have_isa_2_05;
> +static bool have_isa_2_06;
> +#define HAVE_ISA_2_05  have_isa_2_05
> +#define HAVE_ISEL      have_isa_2_06
> +#else
>  #define HAVE_ISA_2_05  0
> -#define HAVE_ISEL      0
> +#define HAVE_ISA_ISEL  0
> +#endif
>  
>  #ifdef CONFIG_USE_GUEST_BASE
>  #define TCG_GUEST_BASE_REG 30
> @@ -2084,6 +2092,16 @@ static const TCGTargetOpDef ppc_op_defs[] = {
>  
>  static void tcg_target_init (TCGContext *s)
>  {
> +#ifdef CONFIG_GETAUXVAL
> +    unsigned long hwcap = getauxval(AT_HWCAP);
> +    /* Bizzarely, the linux kernel doesn't set *all* applicable bits.  */
> +    if (hwcap & PPC_FEATURE_ARCH_2_06) {
> +        have_isa_2_05 = have_isa_2_06 = true;
> +    } else if (hwcap & PPC_FEATURE_ARCH_2_05) {
> +        have_isa_2_05 = true;
> +    }

It's a great idea, but following comments from patch 14, you only have
to check for ARCH_2_06.

I wonder if the same could be used for arm with AT_PLATFORM to detect ARM
v5/v6/v7.

> +#endif
> +
>      tcg_regset_set32 (tcg_target_available_regs[TCG_TYPE_I32], 0, 0xffffffff);
>      tcg_regset_set32 (tcg_target_available_regs[TCG_TYPE_I64], 0, 0xffffffff);
>      tcg_regset_set32 (tcg_target_call_clobber_regs, 0,
> -- 
> 1.8.1.2
> 
> 
> 

-- 
Aurelien Jarno                          GPG: 1024D/F1BCDB73
aurelien@aurel32.net                 http://www.aurel32.net