[PATCH 2/2] sparc: Fix mistakenly cleared PSR[EF] bit.

[Sebastian Huber]

Hello Maksim,

On 06/06/2019 14:43, Maksim Kozlov wrote:
> On Thu, 6 Jun 2019 at 09:57, Sebastian Huber 
> <sebastian.huber at embedded-brains.de 
> <mailto:sebastian.huber at embedded-brains.de>> wrote:
>
>
>
>     On 05/06/2019 21:22, Maksim E. Kozlov wrote:
>     > ---
>     >   cpukit/score/cpu/sparc/cpu_asm.S | 3 ++-
>     >   1 file changed, 2 insertions(+), 1 deletion(-)
>     >
>     > diff --git a/cpukit/score/cpu/sparc/cpu_asm.S
>     b/cpukit/score/cpu/sparc/cpu_asm.S
>     > index 2f3ad24510..69bbfb2748 100644
>     > --- a/cpukit/score/cpu/sparc/cpu_asm.S
>     > +++ b/cpukit/score/cpu/sparc/cpu_asm.S
>     > @@ -682,10 +682,11 @@ isr_dispatch:
>     >           ld      [%g6 + SPARC_PER_CPU_FP_OWNER_OFFSET], %l7
>     >           cmp     %l6, %l7
>     >           bne     .Ldisable_fp
>     > -         andn   %l0, %l5, %l0
>     > +         nop
>
>     Wouldn't it be sufficient to change this to
>
>     bne,a .Ldisable_fp
>       andn %l0, %l5, %l0
>
>     ?
>
>
> Yes, you are right, this is my inattentiveness, and it is enough just 
> to set
> an annul flag.
> If it is needed, I attached modified patch, but if you prefer, you can 
> just add
> this flag yourself.

I still have problems to understand why this patch is necessary. The 
current code is like this:

         /*
          * If we are still the floating point unit owner, then reset the
          * floating point unit owner to NULL, otherwise clear PSR[EF] 
in the
          * interrupt frame and let the FP disabled system call do the 
floating
          * point context save/restore.
          */
         ld      [%g6 + SPARC_PER_CPU_FP_OWNER_OFFSET], %l7
         cmp     %l6, %l7
         bne     .Ldisable_fp
          andn   %l0, %l5, %l0

---> No matter what happens, the PSR[FP] is now cleared in %l0.
---> In this path we are the FPU owner and direct jump to ...

         ba      .Lthread_dispatch_done
          st     %g0, [%g6 + SPARC_PER_CPU_FP_OWNER_OFFSET]

.Ldisable_fp:
         ba      .Lthread_dispatch_done
          st      %l0, [%fp + ISF_PSR_OFFSET]
.Lnon_fp_thread_dispatch:

         call    SYM(_Thread_Do_dispatch)
          mov    %g6, %o0

---> ... here. From now on %l0 is no longer used and ...

#if SPARC_HAS_FPU == 1
.Lthread_dispatch_done:
#endif

         [... %l0 not used ]

---> ... here it is loaded:

         ldd     [%fp + ISF_PSR_OFFSET], %l0    ! restore psr, PC

-- 
Sebastian Huber, embedded brains GmbH

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