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| Standard C Library Functions | sigfpe(3C) |
| | sigfpe - signal handling for specific SIGFPE codes |
SYNOPSIS
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#include <floatingpoint.h>
#include <siginfo.h>
sigfpe_handler_type sigfpe(sigfpe_code_type code, sigfpe_handler_type hdl); |
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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:
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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
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Three steps are required to intercept an IEEE754-related SIGFPE code with sigfpe():
- Set up a handler with sigfpe().
- Enable the relevant IEEE754 trapping capability in the hardware, perhaps by using assembly-language instructions.
- 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(3C).
In a particular program, to avoid confusion, use only one of these interfaces to handle SIGFPE signals.
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| | Example 1. Example Of A User-Specified Signal Handler
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A user-specified signal handler might look like this:
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#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();
}
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and it might be set up like this:
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#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);
}
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/usr/include/floatingpoint.h
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/usr/include/siginfo.h
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See attributes(5) for descriptions of the following
attributes:
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
| MT-Level | Safe |
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sigfpe() returns BADSIG if code is not zero or a defined SIGFPE code.
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