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RE: libstdc++/5625: exception unwinding creates invalid pointer on mips
- From: Ed Maste <emaste at SANDVINE dot com>
- To: echristo at gcc dot gnu dot org
- Cc: gcc-prs at gcc dot gnu dot org,
- Date: 23 Apr 2002 19:36:02 -0000
- Subject: RE: libstdc++/5625: exception unwinding creates invalid pointer on mips
- Reply-to: Ed Maste <emaste at SANDVINE dot com>
The following reply was made to PR libstdc++/5625; it has been noted by GNATS.
From: Ed Maste <emaste@SANDVINE.com>
To: "'echristo@gcc.gnu.org'" <echristo@gcc.gnu.org>,
"'echristo@redhat.com'" <echristo@redhat.com>, Ed Maste
<emaste@SANDVINE.com>, "'gcc-bugs@gcc.gnu.org'" <gcc-bugs@gcc.gnu.org>,
"'gcc-prs@gcc.gnu.org'" <gcc-prs@gcc.gnu.org>, "'gcc-gnats@gcc.gnu.org'"
<gcc-gnats@gcc.gnu.org>
Cc:
Subject: RE: libstdc++/5625: exception unwinding creates invalid pointer o
n mips
Date: Tue, 23 Apr 2002 15:35:33 -0400
Yes, the MIPS documentation states that the destination register
gets the sign-extended result ("GPR[rt]<-sign_extend(temp31..0)").
However, note the ADDIU instruction Restrictions section:
Restrictions:
If GPR rs does not contain a sign-extended
32-bit value (bits 63..31 equal), then the
result of the operation is UNPREDICTABLE.
And then, on page 2:
1.2.1 UNPREDICTABLE
UNPREDICTABLE results may vary from processor
implementation to implementation, instruction
to instruction, or as a function of time on the
same implementation or instruction. Software can
never depend on results that are UNPREDICTABLE.
UNPREDICTABLE operations may cause a result to
be generated or not. If a result is generated,
it is UNPREDICTABLE. UNPREDICTABLE operations
may cause arbitrary exceptions.
-ed
http://www.mips.com/publications/documentation/MD00087-2B-MIPS64BIS-AFP-00.9
5.pdf
(no comma attached to the end of the URL this time!)