Recently I used 'stress-ng --class compute ...' which reported the
failure of the 'logmath clogl' test. It could be reproduced with this
loop which finishes after some random number of iterations:
$ while stress-ng --logmath 1 --logmath-method clogl -t 1; do echo OK; done
stress-ng: info: [6190] setting to a 1 sec run per stressor
...
stress-ng: info: [6190] successful run completed in 1.37 sec
OK
...
OK
stress-ng: info: [6198] setting to a 1 sec run per stressor
stress-ng: info: [6198] dispatching hogs: 1 logmath
stress-ng: fail: [6199] logmath: clogl does not match expected result
stress-ng: error: [6198] logmath: [6199] terminated with an error, exit
status=2 (stressor failed)
...
stress-ng: info: [6198] unsuccessful run completed in 1.37 sec
The value mismatch occurs at the very end when the test loop running
clogl() is hit by the signal indicating timeout.
A closer look shows that the problem could also be reproduced without
any external math function:
$ uname -r
3.5.4-1.x86_64
$ gcc --version
gcc (GCC) 12.4.0
...
$ cat sigtest.c
#include <signal.h>
#include <stdio.h>
static volatile sig_atomic_t sigcnt;
static void sigint_handler(int sig)
{
(void)sig;
sigcnt++;
}
#ifndef WORKS
typedef long double float_type;
#define FMT "La"
#else
typedef double float_type;
#define FMT "a"
#endif
int main()
{
signal(SIGINT, sigint_handler);
volatile float_type x = 0x1.23456789p+0;
while (sigcnt < 42) {
volatile float_type y = x;
volatile float_type d = y - x;
if (d != 0.0)
printf("x = %" FMT ", y = %" FMT ", d = %" FMT "\n", x, y, d);
}
}
$ gcc -o sigtest -O2 sigtest.c
$ ./sigtest > out.txt
(press ^C 42x :-)
$ sort out.txt | uniq -c
3 x = 0x1.23456789p+0, y = -nan, d = -nan
6 x = 0x1.23456789p+0, y = 0x1.23456789p+0, d = -nan
33 x = 0x1.23456789p+0, y = 0x1.23456789p+0, d = 0x0p+0
The problem also occurs if compiled without -O2, but less often. No
problem occurs if compiled with -DWORKS which suggests that only 'long
double' is affected.
--
Regards,
Christian
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