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);

MT-LEVEL

Safe

DESCRIPTION

This 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). 

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

FPE_FLTRESfp_inexact − floating-point inexact result
FPE_FLTDIVfp_division − floating-point division by zero
FPE_FLTUNDfp_underflow − floating-point underflow
FPE_FLTOVFfp_overflow − floating-point overflow
FPE_FLTINVfp_invalid − floating-point invalid operation

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. 

sigfpe() 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(2).  In a particular program, to avoid confusion, use only one of these interfaces to handle SIGFPE signals. 

EXAMPLES

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

SEE ALSO

sigaction(2), signal(2), abort(3C), floatingpoint(5)

DIAGNOSTICS

sigfpe() returns BADSIG if code is not zero or a defined SIGFPE code. 

Sun Microsystems  —  Last change: 13 Jul 1992