SIGFPE(3C) Standard C Library Functions SIGFPE(3C)

sigfpe - signal handling for specific SIGFPE codes

#include <floatingpoint.h>
#include <siginfo.h>
sigfpe_handler_type sigfpe(sigfpe_code_type code,


     sigfpe_handler_type hdl);

The sigfpe() function allows signal handling to be specified for particular SIGFPE codes. A call to sigfpe() defines a new handler hdl for a particular SIGFPE code and returns the old handler as the value of the function sigfpe(). Normally handlers are specified as pointers to functions; the special cases SIGFPE_IGNORE, SIGFPE_ABORT, and SIGFPE_DEFAULT allow ignoring, dumping core using abort(3C), or default handling respectively. Default handling is to dump core using abort(3C).

The code argument is usually one of the five IEEE754-related SIGFPE codes:


FPE_FLTRES   fp_inexact − floating-point inexact result
FPE_FLTDIV   fp_division − floating-point division by zero
FPE_FLTUND   fp_underflow − floating-point underflow
FPE_FLTOVF   fp_overflow − floating-point overflow
FPE_FLTINV   fp_invalid − floating-point invalid operation

And additionally on the x86 architecture:


FPE_FLTDEN   fp_denormalized − floating-point denormalized result

Three steps are required to intercept an IEEE754-related SIGFPE code with sigfpe():

1.
Set up a handler with sigfpe().
2.
Enable the relevant IEEE754 trapping capability in the hardware, perhaps by using assembly-language instructions.
3.
Perform a floating-point operation that generates the intended IEEE754 exception.

The sigfpe() function never changes floating-point hardware mode bits affecting IEEE754 trapping. No IEEE754-related SIGFPE signals will be generated unless those hardware mode bits are enabled.

SIGFPE signals can be handled using sigfpe(), sigaction(2) or signal(3C). In a particular program, to avoid confusion, use only one of these interfaces to handle SIGFPE signals.

Example 1 Example Of A User-Specified Signal Handler

A user-specified signal handler might look like this:


#include <floatingpoint.h>
#include <siginfo.h>
#include <ucontext.h>
/*
* The sample_handler prints out a message then commits suicide.
*/
void
sample_handler(int sig, siginfo_t *sip, ucontext_t *uap) {
	char *label;


        switch (sip−>si_code) {
	case FPE_FLTINV: label = "invalid operand"; break;
	case FPE_FLTRES: label = "inexact"; break;
	case FPE_FLTDIV: label = "division-by-zero"; break;
	case FPE_FLTUND: label = "underflow"; break;
	case FPE_FLTOVF: label = "overflow"; break;
	default: label = "???"; break;
	}
	fprintf(stderr,


        "FP exception %s (0x%x) occurred at address %p.\n",


        label, sip−>si_code, (void *) sip−>si_addr);
	abort();
}

and it might be set up like this:


#include <floatingpoint.h>
#include <siginfo.h>
#include <ucontext.h>
extern void sample_handler(int, siginfo_t *, ucontext_t *);
main(void) {


      sigfpe_handler_type hdl, old_handler1, old_handler2;
/*


 * save current fp_overflow and fp_invalid handlers; set the new
* fp_overflow handler to sample_handler() and set the new
* fp_invalid handler to SIGFPE_ABORT (abort on invalid)
*/


    hdl = (sigfpe_handler_type) sample_handler;


    old_handler1 = sigfpe(FPE_FLTOVF, hdl);


    old_handler2 = sigfpe(FPE_FLTINV, SIGFPE_ABORT);


    ...
/*


 * restore old fp_overflow and fp_invalid handlers


 */


     sigfpe(FPE_FLTOVF, old_handler1);


     sigfpe(FPE_FLTINV, old_handler2);
}

/usr/include/floatingpoint.h

/usr/include/siginfo.h

See attributes(7) for descriptions of the following attributes:

ATTRIBUTE TYPE ATTRIBUTE VALUE
MT-Level Safe

sigaction(2), abort(3C), signal(3C), floatingpoint.h(3HEAD), attributes(7)

The sigfpe() function returns (void(*)())-1 if code is not zero or a defined SIGFPE code.

May 4, 2004 OmniOS