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

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Message-ID: <20130918095003.GB1783@mudshark.cambridge.arm.com>
Date:	Wed, 18 Sep 2013 10:50:03 +0100
From:	Will Deacon <will.deacon@....com>
To:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Russell King <linux@....linux.org.uk>
Subject: Re: Commit breaks strace: ARM: entry: allow ARM-private syscalls to
 be restarted

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)

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