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 22:39:25 +0100 [thread overview]
Message-ID: <20130211213925.GA30998@parrot.com> (raw)
In-Reply-To: <511935BC.8060105@codethink.co.uk>
On Mon, Feb 11, 2013 at 06:17:32PM +0000, Ben Dooks wrote:
> On 02/02/13 08:33, 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.
>
>
> > @@ -43,29 +47,28 @@ ENTRY(memset)
> > #if ! CALGN(1)+0
> >
> > /*
> > - * We need an extra register for this loop - save the return address and
> > - * use the LR
> > + * We need an 2 extra registers for this loop - use r8 and the LR
> > */
> > - str lr, [sp, #-4]!
> > - mov ip, r1
> > + stmfd sp!, {r8, lr}
> > + mov r8, r1
> > mov lr, r1
>
> Out of interest, why not save {r0, lr} and avoid having to
> re-write the entirety of the inner loop?
Because at the inner loop entry, r0 no longer contains the current write pointer: ip is
the current pointer, possibly different from r0 because of the unaligned fixup code.
The idea was to avoid introducing an extra load+store on load/store-free paths; thereby
using a register other than r0 for the current pointer...
BR,
--
Ivan
>
> >
> > 2: subs r2, r2, #64
> > - stmgeia r0!, {r1, r3, ip, lr} @ 64 bytes at a time.
> > - stmgeia r0!, {r1, r3, ip, lr}
> > - stmgeia r0!, {r1, r3, ip, lr}
> > - stmgeia r0!, {r1, r3, ip, lr}
> > + stmgeia ip!, {r1, r3, r8, lr} @ 64 bytes at a time.
> > + stmgeia ip!, {r1, r3, r8, lr}
> > + stmgeia ip!, {r1, r3, r8, lr}
> > + stmgeia ip!, {r1, r3, r8, lr}
> > bgt 2b
> > - ldmeqfd sp!, {pc} @ Now<64 bytes to go.
> > + ldmeqfd sp!, {r8, pc} @ Now<64 bytes to go.
>
>
> --
> Ben Dooks http://www.codethink.co.uk/
> Senior Engineer Codethink - Providing Genius
next prev parent reply other threads:[~2013-02-11 21:39 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
2013-02-11 18:17 ` Ben Dooks
2013-02-11 21:39 ` Ivan Djelic [this message]
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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