From: ivan.djelic@parrot•com (Ivan Djelic)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH] [RFC] arm: fix memset-related crashes caused by recent GCC (4.7.2) optimizations
Date: Mon, 11 Feb 2013 13:35:33 +0100 [thread overview]
Message-ID: <20130211123533.GB28067@parrot.com> (raw)
In-Reply-To: <alpine.LFD.2.02.1302090943440.6300@xanadu.home>
On Sat, Feb 09, 2013 at 02:48:31PM +0000, Nicolas Pitre wrote:
> On Sat, 2 Feb 2013, Ivan Djelic wrote:
>
> > Recent GCC versions (e.g. GCC-4.7.2) perform optimizations based on
> > assumptions about the implementation of memset and similar functions.
> > The current ARM optimized memset code does not return the value of
> > its first argument, as is usually expected from standard implementations.
> >
> > For instance in the following function:
> >
> > void debug_mutex_lock_common(struct mutex *lock, struct mutex_waiter *waiter)
> > {
> > memset(waiter, MUTEX_DEBUG_INIT, sizeof(*waiter));
> > waiter->magic = waiter;
> > INIT_LIST_HEAD(&waiter->list);
> > }
> >
> > compiled as:
> >
> > 800554d0 <debug_mutex_lock_common>:
> > 800554d0: e92d4008 push {r3, lr}
> > 800554d4: e1a00001 mov r0, r1
> > 800554d8: e3a02010 mov r2, #16 ; 0x10
> > 800554dc: e3a01011 mov r1, #17 ; 0x11
> > 800554e0: eb04426e bl 80165ea0 <memset>
> > 800554e4: e1a03000 mov r3, r0
> > 800554e8: e583000c str r0, [r3, #12]
> > 800554ec: e5830000 str r0, [r3]
> > 800554f0: e5830004 str r0, [r3, #4]
> > 800554f4: e8bd8008 pop {r3, pc}
> >
> > GCC assumes memset returns the value of pointer 'waiter' in register r0; causing
> > register/memory corruptions.
> >
> > This patch fixes the return value of the assembly version of memset.
> > Could you please review, or suggest better alternatives ?
> >
> > Thanks,
> >
> > --
> > Ivan
> >
> > (this is a shorter and (hopefully) clearer repost of
> > http://lists.infradead.org/pipermail/linux-arm-kernel/2013-January/144916.html)
> >
> > The patch adds a 'mov' instruction and merges an additional load+store into
> > existing load/store instructions.
> > For ease of review, here is a breakdown of the patch into 4 simple steps:
> >
> > Step 1
> > ======
> > Perform the following substitutions:
> > ip -> r8, then
> > r0 -> ip,
> > and insert 'mov ip, r0' as the first statement of the function.
> > At this point, we have a memset() implementation returning the proper result,
> > but corrupting r8 on some paths (the ones that were using ip).
> >
> > Step 2
> > ======
> > Make sure r8 is saved and restored when (! CALGN(1)+0) == 1:
> >
> > save r8:
> > - str lr, [sp, #-4]!
> > + stmfd sp!, {r8, lr}
> >
> > and restore r8 on both exit paths:
> > - ldmeqfd sp!, {pc} @ Now <64 bytes to go.
> > + ldmeqfd sp!, {r8, pc} @ Now <64 bytes to go.
> > (...)
> > tst r2, #16
> > stmneia ip!, {r1, r3, r8, lr}
> > - ldr lr, [sp], #4
> > + ldmfd sp!, {r8, lr}
> >
> > Step 3
> > ======
> > Make sure r8 is saved and restored when (! CALGN(1)+0) == 0:
> >
> > save r8:
> > - stmfd sp!, {r4-r7, lr}
> > + stmfd sp!, {r4-r8, lr}
> >
> > and restore r8 on both exit paths:
> > bgt 3b
> > - ldmeqfd sp!, {r4-r7, pc}
> > + ldmeqfd sp!, {r4-r8, pc}
> > (...)
> > tst r2, #16
> > stmneia ip!, {r4-r7}
> > - ldmfd sp!, {r4-r7, lr}
> > + ldmfd sp!, {r4-r8, lr}
> >
> > Step 4
> > ======
> > Rewrite register list "r4-r7, r8" as "r4-r8".
> >
> > Signed-off-by: Ivan Djelic <ivan.djelic@parrot•com>
>
> Reviewed-by: Nicolas Pitre <nico@linaro•org>
>
> This is good for the stable tree as well.
>
> Please include in your official commit text the above breakdown
> explanation as well.
OK, will do.
Thanks a lot for reviewing,
--
Ivan
next prev parent reply other threads:[~2013-02-11 12:35 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-02-02 8:33 [PATCH] [RFC] arm: fix memset-related crashes caused by recent GCC (4.7.2) optimizations Ivan Djelic
2013-02-09 11:05 ` Ivan Djelic
2013-02-09 14:48 ` Nicolas Pitre
2013-02-11 12:35 ` Ivan Djelic [this message]
2013-02-11 18:17 ` Ben Dooks
2013-02-11 21:39 ` Ivan Djelic
2013-02-11 18:41 ` Will Deacon
2013-02-11 19:42 ` Ivan Djelic
2013-02-12 14:00 ` Will Deacon
2013-02-12 15:58 ` Russell King - ARM Linux
2013-02-12 16:36 ` Will Deacon
2013-02-12 16:37 ` Russell King - ARM Linux
2013-02-12 16:38 ` Will Deacon
2013-03-05 13:50 ` Dirk Behme
2013-03-06 1:42 ` Will Deacon
2013-03-06 7:05 ` Dirk Behme
2013-03-06 17:11 ` Russell King - ARM Linux
2013-03-06 17:38 ` Dirk Behme
2013-03-06 18:43 ` Russell King - ARM Linux
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