linuxthreads/sysdeps/i386/pt-machine.h

   1 /* Machine-dependent pthreads configuration and inline functions.
   2    i386 version.
   3    Copyright (C) 1996-2001, 2002 Free Software Foundation, Inc.
   4    This file is part of the GNU C Library.
   5    Contributed by Richard Henderson <rth@tamu.edu>.
   6
   7    The GNU C Library is free software; you can redistribute it and/or
   8    modify it under the terms of the GNU Library General Public License as
   9    published by the Free Software Foundation; either version 2 of the
  10    License, or (at your option) any later version.
  11
  12    The GNU C Library is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15    Library General Public License for more details.
  16
  17    You should have received a copy of the GNU Library General Public
  18    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  19    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  20    Boston, MA 02111-1307, USA.  */
  21
  22 #ifndef _PT_MACHINE_H
  23 #define _PT_MACHINE_H   1
  24
  25 #ifndef PT_EI
  26 # define PT_EI extern inline
  27 #endif
  28
  29 /* Get some notion of the current stack.  Need not be exactly the top
  30    of the stack, just something somewhere in the current frame.  */
  31 #define CURRENT_STACK_FRAME  __builtin_frame_address (0)
  32
  33
  34 /* Spinlock implementation; required.  */
  35 PT_EI long int
  36 testandset (int *spinlock)
  37 {
  38   long int ret;
  39
  40   __asm__ __volatile__(
  41        "xchgl %0, %1"
  42        : "=r"(ret), "=m"(*spinlock)
  43        : "0"(1), "m"(*spinlock)
  44        : "memory");
  45
  46   return ret;
  47 }
  48
  49
  50 /* Compare-and-swap for semaphores.
  51    Available on the 486 and above, but not on the 386.
  52    We test dynamically whether it's available or not. */
  53
  54 #define HAS_COMPARE_AND_SWAP
  55 #define TEST_FOR_COMPARE_AND_SWAP
  56
  57 PT_EI int
  58 __compare_and_swap (long int *p, long int oldval, long int newval)
  59 {
  60   char ret;
  61   long int readval;
  62
  63   __asm__ __volatile__ ("lock; cmpxchgl %3, %1; sete %0"
  64                         : "=q" (ret), "=m" (*p), "=a" (readval)
  65                         : "r" (newval), "m" (*p), "a" (oldval)
  66                         : "memory");
  67   return ret;
  68 }
  69
  70
  71 PT_EI int
  72 get_eflags (void)
  73 {
  74   int res;
  75   __asm__ __volatile__ ("pushfl; popl %0" : "=r" (res) : );
  76   return res;
  77 }
  78
  79
  80 PT_EI void
  81 set_eflags (int newflags)
  82 {
  83   __asm__ __volatile__ ("pushl %0; popfl" : : "r" (newflags) : "cc");
  84 }
  85
  86
  87 PT_EI int
  88 compare_and_swap_is_available (void)
  89 {
  90   int oldflags = get_eflags ();
  91   int changed;
  92   /* Flip AC bit in EFLAGS.  */
  93   set_eflags (oldflags ^ 0x40000);
  94   /* See if bit changed.  */
  95   changed = (get_eflags () ^ oldflags) & 0x40000;
  96   /* Restore EFLAGS.  */
  97   set_eflags (oldflags);
  98   /* If the AC flag did not change, it's a 386 and it lacks cmpxchg.
  99      Otherwise, it's a 486 or above and it has cmpxchg.  */
 100   return changed != 0;
 101 }
 102
 103 #endif /* pt-machine.h */