Re: [Qemu-devel] [Bug 696834] [NEW] FP exception reporting not working on NetBSD host

[Paul Goyette]

On Mon, 3 Jan 2011, Paulo Cezar A Junior wrote:

<snip>

>>        printf("FPE signal handler invoked %d times.\n");
>
> this printf() does miss an argument :-)

Yes, it does.  The signal handler is also missing a line:

        siglongjmp(sigfpe_flt_env, 1);

That's what I get for extracting bits&pieces of the larger test program. 
:)


The following is a complete, standalone test program:

        #include <ieeefp.h>
        #include <setjmp.h>
        #include <signal.h>
        #include <stdio.h>

        volatile int flt_signal = 0;

        static sigjmp_buf sigfpe_flt_env;
        static void
        sigfpe_flt_action(int signo, siginfo_t *info, void *ptr)
        {

                flt_signal++;
                siglongjmp(sigfpe_flt_env, 1);
        }
        int main(int argc, void *argv[])
        {
                struct sigaction sa;
                double d;

                printf("Start\n");
                if (sigsetjmp(sigfpe_flt_env, 0) == 0) {
                        sa.sa_flags = SA_SIGINFO;
                        sa.sa_sigaction = sigfpe_flt_action;
                        sigemptyset(&sa.sa_mask);
                        sigaction(SIGFPE, &sa, NULL);
                        fpsetmask(FP_X_INV|FP_X_DZ|FP_X_OFL|FP_X_UFL|FP_X_IMP);
                        d = 1.0 / strtod("0", NULL);
                }
                printf("FPE signal handler invoked %d times.\n");
        }

Executing the program gives the following results:

        # cc -o test test.c
        # ./test
        Start
        FPE signal handler invoked 0 times.
        #

On "real" hardware,

        {225} cc -o test test.c
        {226} ./test
        Start
        FPE signal handler invoked 1 times.
        {227}


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https://bugs.launchpad.net/bugs/696834

Title:
  FP exception reporting not working on NetBSD host

Status in QEMU:
  New

Bug description:
  I recognize that NetBSD is not one of the officially supported host OS.  
However, qemu 0.13.0 is available in the NetBSD pkgsrc collection, and works 
quite well.  Well, with one exception (pun intended): It seems that Floating 
Point exceptions don't get reported properly.

The following code-snippet demonstrates the problem:


volatile int flt_signal = 0;

static sigjmp_buf sigfpe_flt_env;
static void
sigfpe_flt_action(int signo, siginfo_t *info, void *ptr)
{
        flt_signal++;
}

void trigger(void)
{               
        struct sigaction sa;
        double d = strtod("0", NULL);
        
        if (sigsetjmp(sigfpe_flt_env, 0) == 0) {
                sa.sa_flags = SA_SIGINFO;
                sa.sa_sigaction = sigfpe_flt_action;
                sigemptyset(&sa.sa_mask);
                sigaction(SIGFPE, &sa, NULL);
                fpsetmask(FP_X_INV|FP_X_DZ|FP_X_OFL|FP_X_UFL|FP_X_IMP);
                printf("%g\n", 1 / d);
        }
        printf("FPE signal handler invoked %d times.\n");
}