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Date: Fri, 13 Feb 2015 11:55:34 +0100
From: Jan Kiszka <jan.kiszka@siemens.com>
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Subject: Re: [Xenomai] [Xenomai-git] Philippe Gerum : cobalt/x86: exclude
 %rsp from mayday fixup
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To: Philippe Gerum <rpm@xenomai.org>, Xenomai <xenomai@xenomai.org>

On 2015-02-12 18:45, xenomai-git-request@xenomai.org wrote:
> Module: xenomai-3
> Branch: next
> Commit: 667a361408e34b69ea761dcaf0ec8d8081d18cb3
> URL:    http://git.xenomai.org/?p=xenomai-3.git;a=commit;h=667a361408e34b69ea761dcaf0ec8d8081d18cb3
> 
> Author: Philippe Gerum <rpm@xenomai.org>
> Date:   Thu Feb 12 18:39:02 2015 +0100
> 
> cobalt/x86: exclude %rsp from mayday fixup
> 
> ---
> 
>  kernel/cobalt/arch/x86/mayday.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/cobalt/arch/x86/mayday.c b/kernel/cobalt/arch/x86/mayday.c
> index 62c5eea..22a9196 100644
> --- a/kernel/cobalt/arch/x86/mayday.c
> +++ b/kernel/cobalt/arch/x86/mayday.c
> @@ -204,11 +204,12 @@ void xnarch_fixup_mayday(struct xnarchtcb *tcb, struct pt_regs *regs)
>  		test_thread_flag(TIF_IA32)) {
>  		regs->ip = tcb->mayday.ip;
>  		regs->ax = tcb->mayday.ax;
> +		regs->sp = tcb->mayday.sp;
>  	} else
>  		regs->ax = tcb->mayday.ip;
>  #else
>  	regs->ip = tcb->mayday.ip;
>  	regs->ax = tcb->mayday.ax;
> -#endif
>  	regs->sp = tcb->mayday.sp;
> +#endif
>  }

That makes me wonder why we have to save/restore at all? In the end, the
syscall triggered by the ia32 trampoline code doesn't push anything to
the user's stack, does it?

But I'm also confused that my tests without this patch were still
successful...

Jan

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