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.
