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Re: GCC optimizes integer overflow: bug or feature?
From: |
Denis Vlasenko |
Subject: |
Re: GCC optimizes integer overflow: bug or feature? |
Date: |
Tue, 19 Dec 2006 19:48:36 +0100 |
User-agent: |
KMail/1.8.2 |
On Tuesday 19 December 2006 11:37, Paolo Bonzini wrote:
>
> > By the way, as I've tried to describe here:
> > <http://cert.uni-stuttgart.de/advisories/c-integer-overflow.php>
> > variable range tracking can result in reintroduction of
> > supposedly-fixed security vulnerabilities. 8-(
>
> Interesting read. I agree with the proposed fix; however, note that GCC
> does not make the result of overflowing signed left-shifts undefined,
> exactly because in this case the overflow is relied upon by too many
> existing programs (and also because left shifts are inherently a bitwise
> operation, with well defined overflowing behavior on the most
> significant bits).
I wrote this just a few days ago:
do {
int32_t v1 = v << 1;
if (v < 0) v1 ^= mask;
v = v1;
printf("%10u: %08x\n", c++, v);
} while (v != 1);
I would become rather sad if this will stop compiling correctly.
--
vda
- Re: GCC optimizes integer overflow: bug or feature?, (continued)
- Re: GCC optimizes integer overflow: bug or feature?, Robert Dewar, 2006/12/19
- Re: GCC optimizes integer overflow: bug or feature?, Joseph S. Myers, 2006/12/19
- Re: GCC optimizes integer overflow: bug or feature?, Robert Dewar, 2006/12/19
- Re: GCC optimizes integer overflow: bug or feature?, Paolo Bonzini, 2006/12/19
- Re: GCC optimizes integer overflow: bug or feature?, Robert Dewar, 2006/12/19
- Re: GCC optimizes integer overflow: bug or feature?, Robert Dewar, 2006/12/19
- Re: GCC optimizes integer overflow: bug or feature?, Florian Weimer, 2006/12/19
- Re: GCC optimizes integer overflow: bug or feature?, Joseph S. Myers, 2006/12/19
- Re: GCC optimizes integer overflow: bug or feature?, Florian Weimer, 2006/12/19
- Re: GCC optimizes integer overflow: bug or feature?, Robert Dewar, 2006/12/19
- Re: GCC optimizes integer overflow: bug or feature?,
Denis Vlasenko <=
- Re: GCC optimizes integer overflow: bug or feature?, Andrew Haley, 2006/12/19
- Re: GCC optimizes integer overflow: bug or feature?, Denis Vlasenko, 2006/12/20
- Re: GCC optimizes integer overflow: bug or feature?, Robert Dewar, 2006/12/19
- Re: GCC optimizes integer overflow: bug or feature?, Paul Brook, 2006/12/20
- Re: GCC optimizes integer overflow: bug or feature?, Robert Dewar, 2006/12/19
- Re: GCC optimizes integer overflow: bug or feature?, Andrew Pinski, 2006/12/20
- Re: GCC optimizes integer overflow: bug or feature?, Robert Dewar, 2006/12/19
- RE: GCC optimizes integer overflow: bug or feature?, Dave Korn, 2006/12/20
- Re: GCC optimizes integer overflow: bug or feature?, Robert Dewar, 2006/12/19
- Re: GCC optimizes integer overflow: bug or feature?, Mike Stump, 2006/12/20