From mboxrd@z Thu Jan  1 00:00:00 1970
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Date: Sat, 07 Jan 2006 14:33:56 +0100
From: Philippe Gerum <rpm@xenomai.org>
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Subject: Re: [Xenomai-core] [PATCH] Fix ppc fpu support
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To: Heikki Lindholm <holindho@domain.hid>
Cc: xenomai@xenomai.org

Heikki Lindholm wrote:
> Xenomai might preempt linux when linux has cleared a tasks MSR_FP, but 
> not yet set last_task_used_math to NULL. As a result the tasks MSR_FP 
> will get set, although it should be cleared. If the task happens to hit 
> one of the codepaths that save FPU state if MSR_FP is set, the wrong FPU 
> state might be saved to the task. The attached patch should fix this. I 
> couldn't try it on most recent Xenomai trunk, because latency wouldn't 
> build anymore. However, I see no reason it shouldn't work. All thee 
> having trouble with X and Xenomai, give this a shot.
> 

Merged in r383, thanks.

> -- Heikki Lindholm
> 
> 
> ------------------------------------------------------------------------
> 
> diff -Nru xenomai/include/asm-powerpc/system.h xenomai-devel/include/asm-powerpc/system.h
> --- xenomai/include/asm-powerpc/system.h	2006-01-06 15:55:19.000000000 +0200
> +++ xenomai-devel/include/asm-powerpc/system.h	2006-01-06 16:44:53.000000000 +0200
> @@ -55,6 +55,7 @@
>      rthal_fpenv_t fpuenv  __attribute__ ((aligned (16)));
>      rthal_fpenv_t *fpup;	/* Pointer to the FPU backup area */
>      struct task_struct *user_fpu_owner;
> +    unsigned long user_fpu_owner_prev_msr;
>      /* Pointer the the FPU owner in userspace:
>         - NULL for RT K threads,
>         - last_task_used_math for Linux US threads (only current or NULL when MP)
> @@ -368,7 +369,10 @@
>          rthal_save_fpu(tcb->fpup);
>  
>          if(tcb->user_fpu_owner && tcb->user_fpu_owner->thread.regs)
> +            {
> +            tcb->user_fpu_owner_prev_msr = tcb->user_fpu_owner->thread.regs->msr;
>              tcb->user_fpu_owner->thread.regs->msr &= ~MSR_FP;
> +            }
>          }   
>  
>  #endif /* CONFIG_XENO_HW_FPU */
> @@ -383,7 +387,13 @@
>          {
>          rthal_restore_fpu(tcb->fpup);
>  
> -        if(tcb->user_fpu_owner && tcb->user_fpu_owner->thread.regs)
> +	/* Note: Only enable FP in MSR, if it was enabled when we saved the
> +	 * fpu state. We might have preempted Linux when it had disabled FP
> +	 * for the thread, but not yet set last_task_used_math to NULL 
> +	 */
> +        if(tcb->user_fpu_owner && 
> +			tcb->user_fpu_owner->thread.regs &&
> +			((tcb->user_fpu_owner_prev_msr & MSR_FP) != 0))
>              tcb->user_fpu_owner->thread.regs->msr |= MSR_FP;
>          }   
>  
> 
> 
> ------------------------------------------------------------------------
> 
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-- 

Philippe.