Date: Tue, 3 Feb 1998 09:19:34 -0800 (PST) From: Thomas Dean <tomdean@ix.netcom.com> To: malte@webmore.com Cc: bartol@salk.edu, questions@FreeBSD.ORG Subject: Re: IEEE Floating Point question: Inf and NaN Message-ID: <199802031719.JAA00500@ix.netcom.com> In-Reply-To: <3.0.32.19980203083924.02fad158@cyclone.degnet.baynet.de> (message from Malte Lance on Tue, 03 Feb 1998 08:39:25 -0100)
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Catching exceptions with a signal handler does not work in FreeBSD.
The exception mask is cleared BEFORE the user signal handler is called.
In npx.c,
...
*
* XXX the FP state is not preserved across signal handlers. So signal
* handlers cannot afford to do FP unless they preserve the state or
* longjmp() out. Both preserving the state and longjmp()ing may be
* destroyed by IRQ13 bugs. Clearing FP exceptions is not an acceptable
* solution for signals other than SIGFPE.
*/
void
npxintr(unit)
int unit;
{
int code;
struct intrframe *frame;
if (npxproc == NULL || !npx_exists) {
printf("npxintr: npxproc = %p, curproc = %p, npx_exists = %d\n",
npxproc, curproc, npx_exists);
panic("npxintr from nowhere");
}
if (npxproc != curproc) {
printf("npxintr: npxproc = %p, curproc = %p, npx_exists = %d\n",
npxproc, curproc, npx_exists);
panic("npxintr from non-current process");
}
outb(0xf0, 0);
fnstsw(&curpcb->pcb_savefpu.sv_ex_sw);
===> fnclex();
fnop();
/*
* Pass exception to process.
*/
...
So, for the user process to handle exceptions, you must access
curpcb->pcb_savefpu.sv_ex_sw, or modify npx.c to not clear the
exception. I do not think this is a problem with 486+ machines. Can
this be prevented by using the definition of 'cpu' in the config file?
If we have 'cpu "I386_CPU"', then compile the fnclex(), otherwise do
not compile fnclex().
#if defined(I386_CPU)
fnclex();
#endif
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