linux-kernel - Re: [PATCH 3/7] openrisc: restore call-saved regs on sigreturn

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Date:   Mon, 19 Sep 2016 23:50:30 +0900 (JST)
From:   Stafford Horne <shorne@...il.com>
To:     Jonas Bonn <jonas@...thpole.se>
cc:     Stafford Horne <shorne@...il.com>,
        Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/7] openrisc: restore call-saved regs on sigreturn



On Mon, 19 Sep 2016, Jonas Bonn wrote:

> On 09/16/2016 04:43 PM, Stafford Horne wrote:
>>  From: Jonas Bonn <jonas@...thpole.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.

Hi Jonas,
When working through the changelogs to pull out these patches I didnt find 
anything more recent.  However, I did only notice the commit message 
needed cleanup after posting the patch set.  It was on my todo list to 
clean it up.

I will have another look for a later patch, I didnt find at first. But 
thanks for the info.

-Stafford

>>
>>  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@...ke.de>
>>  Signed-off-by: Jonas Bonn <jonas@...thpole.se>
>>  Signed-off-by: Stafford Horne <shorne@...il.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
>
>