sysdeps/m68k/fpu/switch/switch.c

   1 /* Copyright (C) 1991, 1992 Free Software Foundation, Inc.
   2 This file is part of the GNU C Library.
   3
   4 The GNU C Library is free software; you can redistribute it and/or
   5 modify it under the terms of the GNU Library General Public License as
   6 published by the Free Software Foundation; either version 2 of the
   7 License, or (at your option) any later version.
   8
   9 The GNU C Library is distributed in the hope that it will be useful,
  10 but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12 Library General Public License for more details.
  13
  14 You should have received a copy of the GNU Library General Public
  15 License along with the GNU C Library; see the file COPYING.LIB.  If
  16 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  17 Cambridge, MA 02139, USA.  */
  18
  19 #include <ansidecl.h>
  20 #include <signal.h>
  21 #include <68881-sw.h>
  22
  23
  24 /* The signal that is sent when a 68881 instruction
  25    is executed and there is no 68881.  */
  26 #ifndef TRAPSIG
  27 #define TRAPSIG SIGILL
  28 #endif
  29
  30 /* Zero if no 68881, one if we have a 68881, or -1 if we don't know yet.  */
  31 static int have_fpu = -1;
  32
  33
  34 /* Signal handler for the trap that happens if we don't have a 68881.  */
  35 static void
  36 DEFUN(trap, (sig), int sig)
  37 {
  38   have_fpu = 0;
  39 }
  40
  41 /* This function is called by functions that want to switch.
  42    The calling function must be a `struct switch_caller' in data space.
  43    It determines whether a 68881 is present, and modifies its caller
  44    to be a static jump to either the 68881 version or the soft version.
  45    It then returns into the function it has chosen to do the work.  */
  46 void
  47 DEFUN(__68881_switch, (dummy), int dummy)
  48 {
  49   PTR *return_address_location = &((PTR *) &dummy)[-1];
  50   struct switch_caller *CONST caller
  51     = (struct switch_caller *) (((short int *) *return_address_location) - 1);
  52
  53   if (have_fpu < 0)
  54     {
  55       /* Figure out whether or not we have a 68881.  */
  56       __sighandler_t handler = signal (TRAPSIG, trap);
  57       if (handler == SIG_ERR)
  58         /* We can't figure it out, so assume we don't have a 68881.
  59            This assumption will never cause us any problems other than
  60            lost performance, while the reverse assumption could cause
  61            the program to crash.  */
  62         have_fpu = 0;
  63       else
  64         {
  65           /* We set `have_fpu' to nonzero, and then execute a 68881
  66              no-op instruction.  If we have a 68881, this will do nothing.
  67              If we don't have one, this will trap and the signal handler
  68              will clear `have_fpu'.  */
  69           have_fpu = 1;
  70           asm ("fnop");
  71
  72           /* Restore the old signal handler.  */
  73           (void) signal (TRAPSIG, handler);
  74         }
  75     }
  76
  77   /* Modify the caller to be a jump to the appropriate address.  */
  78   caller->insn = JMP;
  79   caller->target = have_fpu ? caller->fpu : caller->soft;
  80
  81   /* Make the address we will return to be the target we have chosen.
  82      Our return will match the `jsr' done by the caller we have
  83      just modified, and it will be just as if that had instead
  84      been a `jmp' to the new target.  */
  85   *return_address_location = caller->target;
  86 }