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From: "marcus.shawcroft at arm dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/48126] arm_output_sync_loop: misplaced memory barrier, missing clrex / dummy strex
Date: Thu, 17 Mar 2011 16:17:00 -0000 [thread overview]
Message-ID: <bug-48126-4-d5GBndCf6O@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-48126-4@http.gcc.gnu.org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48126
Marcus Shawcroft <marcus.shawcroft at arm dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |marcus.shawcroft at arm dot
| |com
--- Comment #1 from Marcus Shawcroft <marcus.shawcroft at arm dot com> 2011-03-17 16:14:36 UTC ---
The code sequence in question looks like this:
dmb sy
1:
ldrex r0, ...
cmp r0, r1
bne 2f
strex r4, r2, ..
teq r4, #0
bne 1b
dmb sy
2:
The ARM Architecture reference manual (section 3.4.5) requires that
there are no explicit memory references between the LDREX and the
STREX, this requirement does not extended to speculative loads in
branch shadows.
An LDREX without a following STREX is explicilty permitted by the
reference manual (section 3.4.5).
The CLREX instruction is provided for use by context switch code in
order to prevent a false positive STREX following a context switch
(section 3.4.4). The inclusion of a CLREX instruction in the above
fragment is not required by the ARM architecture reference manual.
next prev parent reply other threads:[~2011-03-17 16:14 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-03-14 23:12 [Bug target/48126] New: " m.k.edwards at gmail dot com
2011-03-17 16:17 ` marcus.shawcroft at arm dot com [this message]
2011-03-17 18:38 ` [Bug target/48126] " m.k.edwards at gmail dot com
2011-05-24 14:46 ` marcus.shawcroft at arm dot com
2011-05-24 17:05 ` m.k.edwards at gmail dot com
2011-06-22 16:40 ` david.gilbert at linaro dot org
2011-06-22 19:01 ` m.k.edwards at gmail dot com
2011-06-23 9:33 ` marcus.shawcroft at arm dot com
2011-06-24 11:29 ` m.k.edwards at gmail dot com
2011-06-24 13:57 ` ramana at gcc dot gnu.org
2011-10-14 14:40 ` [Bug target/48126] arm_output_sync_loop: misplaced memory barrier rsandifo at gcc dot gnu.org
2011-10-14 14:46 ` rsandifo at gcc dot gnu.org
2012-06-08 6:59 ` jye2 at gcc dot gnu.org
2012-06-19 3:01 ` jye2 at gcc dot gnu.org
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