Re: Libm core dump with SIGILL

[Anders Magnusson <ragge%ludd.ltu.se@localhost>]

Paul Koning skrev den 2015-08-21 16:10:
> > On Aug 21, 2015, at 10:01 AM, Anders Magnusson <ragge%ludd.ltu.se@localhost> wrote:
> >
> > Greg Stark skrev den 2015-08-21 14:35:
> > > While running the Postgres regression tests I found that the exp()
> > > function in libm gets a SIGILL with certain arguments.
> > >
> > > simh$  gcc -Wall  exp.c -lm
> > > simh$ ./a.out
> > > [4]   Illegal instruction (core dumped) ./a.out
> > >
> > > On a modern architecture with IEEE floats:
> > >
> > > $ gcc -Wall  exp.c -lm
> > > $ ./a.out
> > > exp(88.0297) = 1.70141e+38
> > >
> > > I know the VAX floating points are not exactly IEEE and they may not
> > > be able to represent this value but I would expect them to get a FPE
> > > or signal overflow in some other way, not get a SIGILL?
> > Well, not in VAX FP.  From the man page for exp:
> >
> > RETURN VALUES
> >      These functions will return the appropriate computation unless an error
> >      occurs or an argument is out of range.  The functions exp() and expm1()
> >      detect if the computed value will overflow, set the global variable errno
> >      to ERANGE and cause a reserved operand fault on a VAX.
> >
> > So, it is following the specs... :-)
> But SIGILL means illegal instruction, not reserved operand.  Isn't EMODD an optional instruction?  I wonder if the issue is that it's not recognized on Greg's platform so he ends up with the wrong exception.
And what signal is reserved operand on an Unix system? :-)

From trap.c:
        case T_RESOPFLT|T_USER:
                sig = SIGILL;
                code = ILL_ILLOPC;
                break;

-- Ragge