Copyright (c) 1996, Sun Microsystems, Inc.
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#include <floatingpoint.h> #include <siginfo.h> sigfpe_handler_type sigfpe(sigfpe_code_type code, sigfpe_handler_type hdl);
The sigfpe() 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).
The code argument is usually one of the five IEEE\|754-related SIGFPE codes:
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
And additionally on the x86 architecture:
FPE_FLTDEN fp_denormalized - floating-point denormalized result
Three steps are required to intercept an IEEE\|754-related SIGFPE code with sigfpe():
1. Set up a handler with sigfpe().
2. Enable the relevant IEEE\|754 trapping capability in the hardware, perhaps by using assembly-language instructions.
3. Perform a floating-point operation that generates the intended IEEE\|754 exception.
The sigfpe() function never changes floating-point hardware mode bits affecting IEEE\|754 trapping. No IEEE\|754-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.
Example 1 Example Of A User-Specified Signal Handler
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.\en", 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); }
See attributes(5) for descriptions of the following attributes:
| ATTRIBUTE TYPE ATTRIBUTE VALUE |
| MT-Level Safe |
sigaction(2), abort(3C), signal(3C), attributes(5), floatingpoint.h(3HEAD)
The sigfpe() function returns (void(*)())-1 if code is not zero or a defined SIGFPE code.