Re: Libm core dump with SIGILL

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

Paul Koning skrev den 2015-08-21 15:41:
> > On Aug 21, 2015, at 9:29 AM, Greg Stark <stark%mit.edu@localhost> wrote:
> >
> > On Fri, Aug 21, 2015 at 2:24 PM, Johnny Billquist <bqt%update.uu.se@localhost> wrote:
> > > > SIGILL is a compiler bug (if the implementation of exp() is in C) or a
> > > > programmer error (if it's in assembler).
> > >
> > > We should check this. There is trickery going on with VAX FP, in order to
> > > somewhat achieve some of the similar properties of IEEE FP. I know that have
> > > bitten me in the past, and it might even be needed to check in gcc itself,
> > > as the actual libraries might not even be invoked.
> >
> > Sorry, I should have included the versions of things
> >
> > This is on a freshly installed NetBSD 6.1.5 on simh from a recently
> > checked out git tree:
> >
> > simh# uname -a
> > NetBSD simh 6.1.5 NetBSD 6.1.5 (GENERIC) vax
> >
> > simh# gcc --version
> > gcc (GCC) 4.1.3 20080704 prerelease (NetBSD nb3 20111107)
> >
> > $ ./vax -h
> > MicroVAX 3900 simulator V4.0-0 Beta        git commit id: f3af74e4
> >
> > The backtrace is actually a bit deeper than just exp()
> >
> > #0  0x7f7b6984 in infnan (34) from /usr/lib/libm.so.0
> > #1  0x7f7b6810 in scalb (16512, 1179648, 17406, 0) from /usr/lib/libm.so.0
> > #2  0x7f7b66df in exp (255017904, 735823842) from /usr/lib/libm.so.0
> Ok.  It's intentional, but I would call this a design error.  Look at libm/arch/vax/n_infnan.S, it ends in an explicit "reserved operand" error.  Why anyone would do that rather than generating the exception intended for this purpose (floating point error) is unclear.
I assume it is to separate these IEEE-related signals from "native" signals.
The infnan manpage also says that infnan() could be replaced with 
something else if that is desired.

https://www.freebsd.org/cgi/man.cgi?query=infnan&apropos=0&sektion=3&manpath=4.3BSD+NET%2F2&arch=default&format=html

-- Ragge