sysdeps/m68k/fpu/switch/switch.c

   1 /* Copyright (C) 1991, 1992, 1997 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 Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the 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    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, write to the Free
  16    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  17    02111-1307 USA.  */
  18
  19 #include <signal.h>
  20 #include <68881-sw.h>
  21
  22
  23 /* The signal that is sent when a 68881 instruction
  24    is executed and there is no 68881.  */
  25 #ifndef TRAPSIG
  26 #define TRAPSIG SIGILL
  27 #endif
  28
  29 /* Zero if no 68881, one if we have a 68881, or -1 if we don't know yet.  */
  30 static int have_fpu = -1;
  31
  32
  33 /* Signal handler for the trap that happens if we don't have a 68881.  */
  34 static void
  35 trap (sig)
  36      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 __68881_switch (dummy)
  48      int dummy;
  49 {
  50   void **return_address_location = &((void **) &dummy)[-1];
  51   struct switch_caller *const caller
  52     = (struct switch_caller *) (((short int *) *return_address_location) - 1);
  53
  54   if (have_fpu < 0)
  55     {
  56       /* Figure out whether or not we have a 68881.  */
  57       __sighandler_t handler = signal (TRAPSIG, trap);
  58       if (handler == SIG_ERR)
  59         /* We can't figure it out, so assume we don't have a 68881.
  60            This assumption will never cause us any problems other than
  61            lost performance, while the reverse assumption could cause
  62            the program to crash.  */
  63         have_fpu = 0;
  64       else
  65         {
  66           /* We set `have_fpu' to nonzero, and then execute a 68881
  67              no-op instruction.  If we have a 68881, this will do nothing.
  68              If we don't have one, this will trap and the signal handler
  69              will clear `have_fpu'.  */
  70           have_fpu = 1;
  71           asm ("fnop");
  72
  73           /* Restore the old signal handler.  */
  74           (void) signal (TRAPSIG, handler);
  75         }
  76     }
  77
  78   /* Modify the caller to be a jump to the appropriate address.  */
  79   caller->insn = JMP;
  80   caller->target = have_fpu ? caller->fpu : caller->soft;
  81
  82   /* Make the address we will return to be the target we have chosen.
  83      Our return will match the `jsr' done by the caller we have
  84      just modified, and it will be just as if that had instead
  85      been a `jmp' to the new target.  */
  86   *return_address_location = caller->target;
  87 }