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