Re: [Qemu-devel] [PATCH] target-mips: 64-bit FPU for user-mode emulation.

[Petar Jovanovic]

Will there be an update to this patch?
It would be nice to see this in for 1.6.

As of fp64 mode for o32/Rev2, it does not have to be resolved now.

Regards,
Petar

On Sun, 9 Jun 2013, Thomas Schwinge wrote:
> In my reading of the relevant documents, the latter change is not correct
> for o32, and empirically has "interesting" effects on the glibc math
> testsuite, for example.  Keeping the FR register unset for o32 I'm
> proposing to fix with the following patch:

 Correct, unless (until?) the -mfp64 o32 ABI extension is implemented for 
Linux, CP0.Status.FR must remain 0 for o32 programs.

> diff --git target-mips/translate.c target-mips/translate.c
> index 0a53203..51837d4 100644
> --- target-mips/translate.c
> +++ target-mips/translate.c
> @@ -15962,10 +15962,12 @@ void cpu_state_reset(CPUMIPSState *env)
>      if (env->CP0_Config3 & (1 << CP0C3_DSPP)) {
>          env->CP0_Status |= (1 << CP0St_MX);
>      }
> -    /* Enable 64-bit FPU if the target cpu supports it.  */
> +# if defined(TARGET_ABI_MIPSN32) || defined(TARGET_ABI_MIPSN64)
> +    /* Enable 64-bit FPU if the target CPU supports it.  */
>      if (env->active_fpu.fcr0 & (1 << FCR0_F64)) {
>          env->CP0_Status |= (1 << CP0St_FR);

 This is not entirely correct, older 64-bit FPUs, i.e. any before the 
MIPS32/MIPS64 rev. 2 ISA (e.g. R4000, R10000, 5Kf, etc.) won't have the 
CP1.FIR.F64 bit set; it was only defined at that ISA level because for 
earlier architecture revisions the type of the FPU could have been 
inferred from the type of the CPU.  Therefore the condition has to be 
changed, perhaps the best way would simply be just checking in the 
CP0.Status mask if the FR bit is writable.

 Also I suppose there must be an else clause here:

    } else {
        fprintf(stderr, "A 64-bit FPU required for NewABI emulation\n");
        exit(1);

or suchlike because the NewABI mandates full 64-bit FPU operation (or the 
condtion might be changed to an assertion instead and the emulated 
environment checked elsewhere earlier on, because a 64-bit CPU is required 
for NewABI operation anyway and a 64-bit CPU can't ever have a 32-bit FPU 
-- I don't know QEMU well enough to be sure offhand, please check).

>      }
> +# endif
>  #else
>      if (env->hflags & MIPS_HFLAG_BMASK) {
>          /* If the exception was raised from a delay slot,

  Maciej