From: ben.dooks@codethink•co.uk (Ben Dooks)
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 18:17:32 +0000 [thread overview]
Message-ID: <511935BC.8060105@codethink.co.uk> (raw)
In-Reply-To: <1359793988-6881-1-git-send-email-ivan.djelic@parrot.com>
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?
>
> 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 18:17 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 [this message]
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=511935BC.8060105@codethink.co.uk \
--to=ben.dooks@codethink$(echo .)co.uk \
--cc=linux-arm-kernel@lists$(echo .)infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox