[Qemu-devel] Re: [PATCH] tcp/mips: Change TCG_AREG0 (fp -> s0)

[Aurelien Jarno]

On Thu, Apr 08, 2010 at 03:38:52PM +0200, Stefan Weil wrote:
> Register fp is a bad choice for compilations without
> optimisation, because the compiler makes heavy use
> of this register (so the resulting code crashes).

I don't fully understand why the compiler makes use of this register in 
code where env is declared as register fp.

> Register s0 was used for TCG_AREG1 in earlier releases,
> but was no longer used and is now free for TCG_AREG0.
> 
> The resulting code works for compilations without
> optimisation (tested with qemu mips in qemu mips
> on x86 host).

The patch is not complete, at least some changes are missing to 
tcg_target_callee_save_regs.

> Cc: Aurelien Jarno <address@hidden>
> Signed-off-by: Stefan Weil <address@hidden>
> ---
>  dyngen-exec.h         |    2 +-
>  tcg/mips/tcg-target.h |    2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/dyngen-exec.h b/dyngen-exec.h
> index b9f6969..85a2616 100644
> --- a/dyngen-exec.h
> +++ b/dyngen-exec.h
> @@ -61,7 +61,7 @@ extern int printf(const char *, ...);
>  #elif defined(__hppa__)
>  #define AREG0 "r17"
>  #elif defined(__mips__)
> -#define AREG0 "fp"
> +#define AREG0 "s0"
>  #elif defined(__sparc__)
>  #ifdef CONFIG_SOLARIS
>  #define AREG0 "g2"
> diff --git a/tcg/mips/tcg-target.h b/tcg/mips/tcg-target.h
> index 0292d33..0028bfa 100644
> --- a/tcg/mips/tcg-target.h
> +++ b/tcg/mips/tcg-target.h
> @@ -97,7 +97,7 @@ enum {
>  #undef TCG_TARGET_HAS_ext16u_i32   /* andi rt, rs, 0xffff */
>  
>  /* Note: must be synced with dyngen-exec.h */
> -#define TCG_AREG0 TCG_REG_FP
> +#define TCG_AREG0 TCG_REG_S0
>  
>  /* guest base is supported */
>  #define TCG_TARGET_HAS_GUEST_BASE
> -- 
> 1.5.6.5
> 
> 

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