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Roland McGrath
1995-02-18 01:27:10 +00:00
commit 28f540f45b
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sysdeps/m68k/fpu/switch/switch.c Normal file
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/* Copyright (C) 1991, 1992 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public License as
published by the Free Software Foundation; either version 2 of the
License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Library General Public License for more details.
You should have received a copy of the GNU Library General Public
License along with the GNU C Library; see the file COPYING.LIB. If
not, write to the Free Software Foundation, Inc., 675 Mass Ave,
Cambridge, MA 02139, USA. */
#include <ansidecl.h>
#include <signal.h>
#include <68881-sw.h>
/* The signal that is sent when a 68881 instruction
is executed and there is no 68881. */
#ifndef TRAPSIG
#define TRAPSIG SIGILL
#endif
/* Zero if no 68881, one if we have a 68881, or -1 if we don't know yet. */
static int have_fpu = -1;
/* Signal handler for the trap that happens if we don't have a 68881. */
static void
DEFUN(trap, (sig), int sig)
{
have_fpu = 0;
}
/* This function is called by functions that want to switch.
The calling function must be a `struct switch_caller' in data space.
It determines whether a 68881 is present, and modifies its caller
to be a static jump to either the 68881 version or the soft version.
It then returns into the function it has chosen to do the work. */
void
DEFUN(__68881_switch, (dummy), int dummy)
{
PTR *return_address_location = &((PTR *) &dummy)[-1];
struct switch_caller *CONST caller
= (struct switch_caller *) (((short int *) *return_address_location) - 1);
if (have_fpu < 0)
{
/* Figure out whether or not we have a 68881. */
__sighandler_t handler = signal (TRAPSIG, trap);
if (handler == SIG_ERR)
/* We can't figure it out, so assume we don't have a 68881.
This assumption will never cause us any problems other than
lost performance, while the reverse assumption could cause
the program to crash. */
have_fpu = 0;
else
{
/* We set `have_fpu' to nonzero, and then execute a 68881
no-op instruction. If we have a 68881, this will do nothing.
If we don't have one, this will trap and the signal handler
will clear `have_fpu'. */
have_fpu = 1;
asm ("fnop");
/* Restore the old signal handler. */
(void) signal (TRAPSIG, handler);
}
}
/* Modify the caller to be a jump to the appropriate address. */
caller->insn = JMP;
caller->target = have_fpu ? caller->fpu : caller->soft;
/* Make the address we will return to be the target we have chosen.
Our return will match the `jsr' done by the caller we have
just modified, and it will be just as if that had instead
been a `jmp' to the new target. */
*return_address_location = caller->target;
}