NAME

sigfpe - signal handling for specific SIGFPE codes

SYNOPSIS

#include <signal.h>

#include <floatingpoint.h>

sigfpe_handler_type sigfpe(sigfpe_code_type code, sigfpe_handler_type hdl);

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, specifying core dump using abort(3C), or default handling respectively. 

For these IEEE-related codes:

FPE_FLTINEX_TRAPfp_inexact - floating inexact result
FPE_FLTDIV_TRAPfp_division - floating division by zero
FPE_FLTUND_TRAPfp_underflow - floating underflow
FPE_FLTOVF_TRAPfp_overflow - floating overflow
FPE_FLTBSUN_TRAPfp_invalid - branch or set on unordered
FPE_FLTOPERR_TRAPfp_invalid - floating operand error
FPE_FLTNAN_TRAPfp_invalid - floating Not-A-Number

default handling is defined to be to call the handler specified to ieee_handler(3M). 

For all other SIGFPE codes, default handling is to core dump using abort(3C). 

The compilation option −ffpa causes fpa recomputation to replace the default abort action for code FPE_FPA_ERROR.  Note: SIGFPE_DEFAULT will restore abort rather than FPA recomputation for this code. 

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

1) Set up a handler with sigfpe(). 

2) Enable the relevant IEEE trapping capability in the hardware, perhaps by using assembly-language instructions. 

3) Perform a floating-point operation that generates the intended IEEE exception. 

Unlike ieee_handler(3M), sigfpe() never changes floating-point hardware mode bits affecting IEEE trapping.  No IEEE-related SIGFPE signals will be generated unless those hardware mode bits are enabled. 

SIGFPE signals can be handled using sigfpe(), signal(2), sigvec(3B), or ieee_handler(3M).  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:

void sample_handler(int sig, int code, struct sigcontext ∗scp, char ∗addr) {
/∗
   Sample user-written sigfpe code handler.
   Prints a message and continues.
   struct sigcontext is defined in <signal.h>.
∗/
printf(" ieee exception code %x occurred at pc %X \n",code,scp->sc_pc);
}

and it might be set up like this:
extern void sample_handler(int, int, struct sigcontext ∗, char ∗);
 main(void) {
sigfpe_handler_type hdl, old_handler1, old_handler2;
/∗
∗ save current overflow and invalid handlers; set the new
∗ overflow handler to sample_handler() and set the new
∗ invalid handler to SIGFPE_ABORT (abort on invalid)
∗/
hdl = (sigfpe_handler_type) sample_handler;
old_handler1 = sigfpe(FPE_FLTOVF_TRAP, hdl);
old_handler2 = sigfpe(FPE_FLTOPERR_TRAP, SIGFPE_ABORT);
...
/∗
∗ restore old overflow and invalid handlers
∗/
sigfpe(FPE_FLTOVF_TRAP,   old_handler1);
sigfpe(FPE_FLTOPERR_TRAP, old_handler2);
}

FILES

/opt/SUNWspro/SC2.0/include/cc/floatingpoint.h

/usr/include/signal.h

SEE ALSO

signal(2), abort(3C), floatingpoint(3B), ieee_handler(3M), sigvec(3B)

DIAGNOSTICS

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

SunOS 5.1  —  Last change: 13 Jul 1992