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SubjectRe: [PATCH 3/7] openrisc: restore call-saved regs on sigreturn
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On 09/16/2016 04:43 PM, Stafford Horne wrote:
> From: Jonas Bonn <jonas@southpole.se>
>
> Return to userspace via _resume_userspace instead of via syscall return
> path for the rt_sigreturn syscall.
>
> I'll rework this comment more later, but this patch needs testing.

This whole patch was reworked later... what happened to that work? I
recall it being posted for testing without feedback...

In any case, the patch comment needs cleaning up.

/Jonas

>
> Old comment from previous patch:
>
> The sigreturn syscall is more like a context switch than a function call;
> it entails a return from one context (the signal handler) to another
> (the process in question). For a context switch like this there are
> effectively no call-saved regs that remain constant across the transition.
>
> This patch restores the call-saved regs from pt_regs before returning from
> the syscall, effectively restoring the context that the process had before
> being interrupted by the signal handler. Restoring the call-saved regs
> in this way allows us to return to userspace via the usual syscall fast
> path.
>
> Reported-by: Sebastian Macke <sebastian@macke.de>
> Signed-off-by: Jonas Bonn <jonas@southpole.se>
> Signed-off-by: Stafford Horne <shorne@gmail.com>
> ---
> arch/openrisc/kernel/entry.S | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/arch/openrisc/kernel/entry.S b/arch/openrisc/kernel/entry.S
> index fec8bf9..572d223 100644
> --- a/arch/openrisc/kernel/entry.S
> +++ b/arch/openrisc/kernel/entry.S
> @@ -1101,8 +1101,16 @@ ENTRY(__sys_fork)
> l.addi r3,r1,0
>
> ENTRY(sys_rt_sigreturn)
> - l.j _sys_rt_sigreturn
> + l.jal _sys_rt_sigreturn
> l.addi r3,r1,0
> + l.sfne r30,r0
> + l.bnf _no_syscall_trace
> + l.nop
> + l.jal do_syscall_trace_leave
> + l.addi r3,r1,0
> +_no_syscall_trace:
> + l.j _resume_userspace
> + l.nop
>
> /* This is a catch-all syscall for atomic instructions for the OpenRISC 1000.
> * The functions takes a variable number of parameters depending on which

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