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

NAME

sigfpe - signal handling for specific SIGFPE codes

SYNOPSIS

#include <floatingpoint.h>
#include <siginfo.h>

sigfpe_handler_type sigfpe(sigfpe_code_type code,
sigfpe_handler_type hdl);

DESCRIPTION

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.

EXAMPLES

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);
}

FILES

/usr/include/floatingpoint.h


/usr/include/siginfo.h

ATTRIBUTES

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


+---------------+-----------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+-----------------+
|MT-Level | Safe |
+---------------+-----------------+

SEE ALSO

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

DIAGNOSTICS

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

May 4, 2004 SIGFPE(3C)