On Sat, Jan 22, 2011 at 3:30 PM, Mateusz Loskot <mate...@loskot.net> wrote: > On 18/01/11 21:51, Blue Swirl wrote: >> On Tue, Jan 18, 2011 at 6:00 PM, Mateusz Loskot <mate...@loskot.net> wrote: >>> On 18/01/11 17:36, Blue Swirl wrote: >>>> >>>> On Tue, Jan 18, 2011 at 3:27 PM, Mateusz Loskot<mate...@loskot.net> >>>> 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 >>> >>> I just tested on NetBSD 5.0/SPARC under QEMU 0.13 (same version I use with >>> NetBSD 5.1/SPARC) and it works well indeed: >>> >>> mloskot@qemu-netbsd-50-sparc:~/tmp# ./a.out >>> is a number >>> nan >>> mloskot@qemu-netbsd-50-sparc:~/tmp# >>> >>> Hmm, this is becoming interesting. >>> >>> I run QEMU 0.13 on Windows Vista (64-bit). >>> Perhaps host system and QEMU binaries are relevant here. >>> I will try on Linux host system later tonight. >>> >>> BTW, here are my images: >>> >>> http://mateusz.loskot.net/tmp/qemu/ >> >> The problem was with NaN handling in fcmped instruction. I've >> committed a patch that fixes the problem, please test. Thanks for >> reporting and the test case. > > FYI, this problem seems to be occurring in qemu on Windows only. > I tested git version dated before you applied the fix > and built on Linux and the problem does not happening there.
No, it was generic problem. I could reproduce it with your test case and with a small assembler program which only used fcmped using user emulator.
