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From: "bernd.edlinger at hotmail dot de" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/56997] Incorrect write to packed field when strict-volatile-bitfields enabled on aarch32
Date: Sun, 23 Jun 2013 18:02:00 -0000 [thread overview]
Message-ID: <bug-56997-4-CF9apqmZv5@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-56997-4@http.gcc.gnu.org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56997
Bernd Edlinger <bernd.edlinger at hotmail dot de> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |bernd.edlinger at hotmail dot de
--- Comment #6 from Bernd Edlinger <bernd.edlinger at hotmail dot de> ---
(In reply to Sandra Loosemore from comment #5)
> Patch posted here:
http://gcc.gnu.org/ml/gcc-patches/2013-06/msg00750.html
Hi Sandra,
I tried your patch, but I dont like the code that it generates:
printf("%x\n", (unsigned int)g.b);
g.b = 0xAAAAAAA;
is compiled to invalid code (in ARMv5)
ldr r4, .L2
ldr r1, [r4]
ldr r3, [r4, #4]
and r3, r3, #7
mov r3, r3, asl #25
orr r1, r3, r1, lsr #7
ldr r0, .L2+4
bl printf
ldr r2, [r4]
ldr r3, .L2+8
and r2, r2, #127
orr r3, r2, r3
str r3, [r4]
ldr r3, [r4, #4]
bic r3, r3, #7
orr r3, r3, #5
str r3, [r4, #4]
code is invalid because: the object "g" is only 5 bytes large,
but the first statement reads 2x4 bytes, and ignores the 3 extra bytes.
this can fault if g is close to a segment boundary.
The second statement reads the 3 bytes beyond g and writes them
unmodified back. That is problematic if a task switch occurs between the
read and store sequence, and the other task modifies something in the 3 bytes.
Previous versions of gcc produced single 5x1 byte read/write sequences for
that structure, as does apparently the x86 version.
Regards
Bernd.
next prev parent reply other threads:[~2013-06-23 18:02 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-04-18 8:05 [Bug target/56997] New: " joey.ye at arm dot com
2013-04-18 8:12 ` [Bug target/56997] " joey.ye at arm dot com
2013-04-18 8:26 ` rguenth at gcc dot gnu.org
2013-04-18 8:46 ` joey.ye at arm dot com
2013-06-08 19:59 ` sandra at codesourcery dot com
2013-06-14 3:01 ` sandra at codesourcery dot com
2013-06-23 18:02 ` bernd.edlinger at hotmail dot de [this message]
2013-06-23 22:03 ` bernd.edlinger at hotmail dot de
2013-06-24 0:03 ` sandra at codesourcery dot com
2013-06-24 20:27 ` bernd.edlinger at hotmail dot de
2013-06-25 11:35 ` bernd.edlinger at hotmail dot de
2013-08-28 20:43 ` ramana at gcc dot gnu.org
2013-10-07 15:42 ` sandra at codesourcery dot com
2013-12-11 16:50 ` edlinger at gcc dot gnu.org
2013-12-11 16:59 ` edlinger at gcc dot gnu.org
2014-01-07 10:12 ` joey.ye at arm dot com
2014-02-27 7:28 ` jye2 at gcc dot gnu.org
2014-08-15 4:46 ` pinskia at gcc dot gnu.org
2014-08-15 16:36 ` bernd.edlinger at hotmail dot de
2015-04-04 15:28 ` bernd.edlinger at hotmail dot de
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