Re: [Qemu-devel] [sparc] Floating point exception issue

[Blue Swirl]

On Tue, Jan 18, 2011 at 3:27 PM, Mateusz Loskot <address@hidden> wrote:
> Hi,
>
> Recently, I have reported mysterious issues on NetBSD 5.1
> emulated on SPARC. The whole first thread is here:
>
> http://lists.gnu.org/archive/html/qemu-devel/2011-01/msg01509.html
>
> I decided to investigate the problem deeper and with great help
> from NetBSD folks, I managed to find reproducible test case.
> Initially, it was AWK command:
>
> # echo NaN | awk '{print "test"}'
> awk: floating point exception 8
>  source line number 1
>
> and next it boiled down to simple C program (see below).
> Details of the investigation are archived in the NetBSD Problem
> Report #44389 here:
>
> http://gnats.netbsd.org/cgi-bin/query-pr-single.pl?number=44389
>
>
> Here is final version of the test program which reproduces the problem:
>
> #include <stdio.h>
> #include <stdlib.h>
> #include <math.h>
> #include <errno.h>
>
> int is_number(const char *s)
> {
>        double r;
>        char *ep;
>        errno = 0;
>        r = strtod(s, &ep);
>        if (r == HUGE_VAL)
>                printf("X:%g\n", r);
>
>        if (ep == s || r == HUGE_VAL || errno == ERANGE)
>                return 0;
>        while (*ep == ' ' || *ep == '\t' || *ep == '\n')
>                ep++;
>        if (*ep == '\0')
>                return 1;
>        else
>                return 0;
> }
>
> int main(int argc, char **argv)
> {
>        double v;
>
>        if (is_number("NaN")) {
>                printf("is a number\n");
>                v = atof("NaN");
>        } else {
>                printf("not a number\n");
>                v = 0.0;
>        }
>        printf("%.4f\n", v);
>
>        return 0;
> }
>
>
> On NetBSD/SPARC, the program receives SIGFPE:
>
> $ gcc ./nan_test_2.c
>  $ ./a.out
>  [1]   Floating point exception (core dumped) ./a.out
>
> Specifically, it's caused by r == HUGE_VAL condition in
>  if (ep == s || r == HUGE_VAL || errno == ERANGE)
> where r is NaN.
>
> All the signs indicate there is a bug in QEMU.

I'll install 5.1, but on 4.0 which I had installed, the program works fine:
$ ./sigfpe
is a number
nan