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Re: how to make gcc warn about arithmetic signed overflow
- From: Oleg Endo <oleg dot endo at t-online dot de>
- To: Dave Allured - NOAA Affiliate <dave dot allured at noaa dot gov>
- Cc: gcc-help at gcc dot gnu dot org
- Date: Mon, 23 Sep 2013 21:42:44 +0200
- Subject: Re: how to make gcc warn about arithmetic signed overflow
- Authentication-results: sourceware.org; auth=none
- References: <20130921164609 dot GC3086 at a dot lan> <CAH6eHdTToM+TMy55m5HYo39DC8nA0RrTma1Bp5OnhUtPErMfOA at mail dot gmail dot com> <20130921174229 dot GD3086 at a dot lan> <CAH6eHdQzJNQY4Meysi259RheSaGscKUF28OW43OvOD1rf6FkxQ at mail dot gmail dot com> <20130923000355 dot fa2a964c dot jklowden at schemamania dot org> <CALqwTFMfRi6sZY6Ffpdp0E4d4xiJT0EHRUQH-+Oph5c5AWR3-Q at mail dot gmail dot com>
On Mon, 2013-09-23 at 13:38 -0600, Dave Allured - NOAA Affiliate wrote:
> On Sun, Sep 22, 2013 at 10:03 PM, James K. Lowden
> <jklowden@schemamania.org> wrote:
> > Regarding the OP's query
> >
> >> > int r = ab * bc;
> >
> > although the provided example is simple enough, it's the compiler's
> > job is to generate object code, not to do static analysis.
> >
> > Even if the values are const, in the general case they could be
> > modified by another module or another thread. The compiler simply
> > doesn't have enough information to warn of every runtime overflow.
>
> I believe the CPU overflow flag is updated after most integer
> arithmetic instructions. Does GCC have any facility for checking this
> flag after each integer operation? This would be a runtime check, of
> course, not a compile time check.
>
See -ftrapv option. Although trapping math is not supported on every
target properly.
E.g. http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35412
or SH related http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54272
Cheers,
Oleg