NAME

sigfpe − signal handling for specific SIGFPE codes

SYNOPSIS

/usr/ucb/cc  [ flag. . . ] file . . .

#include <signal.h>

#include <floatingpoint.h>

sigfpe_handler_type sigfpe(code, hdl)
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(3), or default handling respectively. 

For these IEEE-related codes:

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(3). 

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 sigvec(2), signal(3), sigfpe(3), or ieee_handler(3M).  In a particular program, to avoid confusion, use only one of these interfaces to handle SIGFPE signals. 

EXAMPLE

A user-specified signal handler might look like this:

void sample_handler( sig, code, scp, addr )
int sig ;/∗ sig == SIGFPE always ∗/
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;
 main
{
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

/usr/include/floatingpoint.h

/usr/include/signal.h

SEE ALSO

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

RETURN VALUE

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

  —  BSD Compatibility Package