sigfpe(3B)

NAME

sigfpe − signal handling for specific SIGFPE codes

SYNOPSIS

/usr/ucb/cc [ flag ... ] file ...

#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_inexactfloating inexact result
FPE_FLTDIV_TRAPfp_divisionfloating division by zero
FPE_FLTUND_TRAPfp_underflowfloating underflow
FPE_FLTOVF_TRAPfp_overflowfloating overflow
FPE_FLTBSUN_TRAPfp_invalidbranch or set on unordered
FPE_FLTOPERR_TRAPfp_invalidfloating operand error
FPE_FLTNAN_TRAPfp_invalidfloating Not-A-Number

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.

SIGFPE signals can be handled using sigvec(3B), signal(2), sigfpe(3B). 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( 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;
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);
}

RETURN VALUES

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

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