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From: "michael.hope at linaro dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/49169] New: ARM: optimisations strip the Thumb/ARM mode bit off function pointers
Date: Thu, 26 May 2011 02:23:00 -0000 [thread overview]
Message-ID: <bug-49169-4@http.gcc.gnu.org/bugzilla/> (raw)
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49169
Summary: ARM: optimisations strip the Thumb/ARM mode bit off
function pointers
Product: gcc
Version: 4.6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
AssignedTo: unassigned@gcc.gnu.org
ReportedBy: michael.hope@linaro.org
ARM devices encode the instruction set mode in the LSB of the function address.
Functions are word aligned on ARM. If you try to test the LSB of a function
pointer then GCC assumes that the two least significant bits are zero and
optimises away the test.
This problem is seen in Mono and was originally reported at:
https://bugs.launchpad.net/ubuntu/+source/gcc-4.5/+bug/721531
A reduced test case is:
void main() {
void *p = main;
if ((int)p & 1) printf ("HIT!\n");
}
When compiled with -march=armv7-a -mthumb -O0 then the word 'HIT!' will show.
When compiled with -O2, the branch is not taken.
The problem does not occur in 4.4.5. It does occur in 4.5.2, 4.6.0, and trunk
r174044.
next reply other threads:[~2011-05-26 2:13 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-05-26 2:23 michael.hope at linaro dot org [this message]
2011-05-26 7:59 ` [Bug rtl-optimization/49169] " mikpe at it dot uu.se
2011-05-26 8:22 ` rguenth at gcc dot gnu.org
2011-05-26 8:48 ` rguenth at gcc dot gnu.org
2011-06-07 7:33 ` rsandifo at gcc dot gnu.org
2011-06-27 9:34 ` rsandifo at gcc dot gnu.org
2011-07-08 15:05 ` ramana at gcc dot gnu.org
2011-09-19 9:00 ` jye2 at gcc dot gnu.org
2012-07-31 1:00 ` ramana at gcc dot gnu.org
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