Messages in this thread |  | | Subject | 2.4, arch-dependent floating point exception and trap handling | From | Daniel Barlow <> | Date | Tue, 30 Jul 2002 14:06:57 +0100 |
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I'm seeing discrepancies between the way that floating point exceptions are handled on different architectures. Briefly, I have a program that uses the glibc function feenableexcept() to enable SIGFPE on divide-by-zero errors, then installs a SIGFPE handler that uses sigsetjmp/siglongjmp, then divides 1.0 by 0.0 twice.
What I expect to happen is for my signal handler to be called twice. What actually happens varies:
On Alpha: 2.4.19-pre1-ac2, gcc version 2.95.4 20011002, PCA56 (SX164)
:; cc -o foo foo.c -lm -mieee foo.c: In function `main': foo.c:23: warning: assignment from incompatible pointer type :; ./foo exceptions enabled: 0 exceptions enabled: 40000 hello in handler abort in handler abort terminating
- exactly as expected
On x86: 2.4.19-rc1, gcc version 2.95.4 20011002 , Pentium III (Coppermine)
my signal handler is called the first time, and then the second attempt gets "inf". I've run this under gdb as well; the second SIGFPE is not received by the process
:; gcc -o foo foo.c -lm foo.c: In function `main': foo.c:23: warning: assignment from incompatible pointer type :; ./foo exceptions enabled: 0 exceptions enabled: 4 hello in handler abort a/b=inf terminating
On PPC: 2.4.19-pre8, gcc version 2.95.4 20011002, 266MHz 740/750 rev 2.2 (tangerine iMac) I have x86-like behaviour
:; cc -o foo foo.c -lm foo.c: In function `main': foo.c:23: warning: assignment from incompatible pointer type :; ./foo exceptions enabled: 0 exceptions enabled: 4000000 hello in handler abort a/b=inf terminating
All of these are uniprocessor machines running uniprocessor kernels. The behaviour I'd like _most_ is for the pre-signal environment to be restored, but at least to get the same behaviour everywhere would be a good thing.
I append the test program I've been using so you can tell me whether my whole approach is misguided
---cut here--- #include <signal.h> #include <stdio.h> #include <sys/signal.h> #include <ucontext.h> #include <fenv.h> #include <setjmp.h>
sigjmp_buf env; double a=1.0,b=0.0;
int handler(int signal, struct siginfo *info, struct ucontext *context) { printf("in handler\n"); siglongjmp(env,signal); }
main() { struct sigaction sa;
a=1.0; printf("exceptions enabled: %x\n", fegetexcept()); feenableexcept(FE_DIVBYZERO); printf("exceptions enabled: %x\n", fegetexcept()); sa.sa_sigaction = handler; sigemptyset(&sa.sa_mask); sa.sa_flags = SA_SIGINFO | SA_RESTART; sigaction(SIGFPE, &sa, NULL); printf("hello\n"); /* first time */ if(sigsetjmp(env,1)) printf("abort\n"); else printf("a/b=%f\n", a/b);
/* now try again, see if things were restored */ if(sigsetjmp(env,1)) printf("abort\n"); else printf("a/b=%f\n", a/b); printf("terminating\n"); }
--- cut here ---
If this message should have been sent elsewhere (e.g. to port-specific lists or maintainers) please feel free to tell me where and/or to forward it.
Thanks!
-dan
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