linux-kernel - Re: Commit breaks strace: ARM: entry: allow ARM-private syscalls to be restarted

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Date:	Fri, 4 Oct 2013 19:24:48 +0200
From:	Arokux X <arokux@...il.com>
To:	Will Deacon <will.deacon@....com>
Cc:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	Russell King <linux@....linux.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: Commit breaks strace: ARM: entry: allow ARM-private syscalls to
 be restarted

On Wed, Sep 18, 2013 at 11:50 AM, Will Deacon <will.deacon@....com> wrote:
> On Wed, Sep 18, 2013 at 10:17:48AM +0100, Will Deacon wrote:
>> On Tue, Sep 17, 2013 at 10:57:49PM +0100, Jason Gunthorpe wrote:
>> > This happens with the latest git head for strace, as well as the 4.7
>> > release.
>> >
>> > Hopefully you can cook up a fix :)
>>
>> I'll take a look today, thanks.
>
> Ok, looks like the backwards branch to the syscall dispatching logic from
> the trace entry is busted. Can you try the patch below please?
>
> I might also take a look at unifying the function prototypes for arm_syscall
> and syscall_trace_enter, since it should help us remove some of the argument
> shuffling in the trace path.
>
> Will
>
> --->8
>
> diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
> index 74ad15d1..bc6bd96 100644
> --- a/arch/arm/kernel/entry-common.S
> +++ b/arch/arm/kernel/entry-common.S
> @@ -442,10 +442,10 @@ local_restart:
>         ldrcc   pc, [tbl, scno, lsl #2]         @ call sys_* routine
>
>         add     r1, sp, #S_OFF
> -       cmp     scno, #(__ARM_NR_BASE - __NR_SYSCALL_BASE)
> +2:     cmp     scno, #(__ARM_NR_BASE - __NR_SYSCALL_BASE)
>         eor     r0, scno, #__NR_SYSCALL_BASE    @ put OS number back
>         bcs     arm_syscall
> -2:     mov     why, #0                         @ no longer a real syscall
> +       mov     why, #0                         @ no longer a real syscall
>         b       sys_ni_syscall                  @ not private func
>
>  #if defined(CONFIG_OABI_COMPAT) || !defined(CONFIG_AEABI)

Just stumbled upon the same issue. The patch seems to cure the problem. Thanks.
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