how to make gcc warn about arithmetic signed overflow

Oleg Endo oleg.endo@t-online.de
Mon Sep 23 19:43:00 GMT 2013


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



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