linuxthreads/sysdeps/i386/pt-machine.h

   1 /* Machine-dependent pthreads configuration and inline functions.
   2    i386 version.
   3    Copyright (C) 1996-2001, 2002, 2003 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 Lesser General Public License as
   9    published by the Free Software Foundation; either version 2.1 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    Lesser General Public License for more details.
  16
  17    You should have received a copy of the GNU Lesser 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 __ASSEMBLER__
  26 #ifndef PT_EI
  27 # define PT_EI extern inline __attribute__ ((always_inline))
  28 #endif
  29
  30 extern long int testandset (int *spinlock);
  31 extern int __compare_and_swap (long int *p, long int oldval, long int newval);
  32
  33 /* Get some notion of the current stack.  Need not be exactly the top
  34    of the stack, just something somewhere in the current frame.  */
  35 #define CURRENT_STACK_FRAME  __builtin_frame_address (0)
  36
  37
  38 /* Spinlock implementation; required.  */
  39 PT_EI long int
  40 testandset (int *spinlock)
  41 {
  42   long int ret;
  43
  44   __asm__ __volatile__(
  45        "xchgl %0, %1"
  46        : "=r"(ret), "=m"(*spinlock)
  47        : "0"(1), "m"(*spinlock)
  48        : "memory");
  49
  50   return ret;
  51 }
  52
  53
  54 /* Compare-and-swap for semaphores.
  55    Available on the 486 and above, but not on the 386.
  56    We test dynamically whether it's available or not. */
  57
  58 #define HAS_COMPARE_AND_SWAP
  59 #define TEST_FOR_COMPARE_AND_SWAP
  60
  61 PT_EI int
  62 __compare_and_swap (long int *p, long int oldval, long int newval)
  63 {
  64   char ret;
  65   long int readval;
  66
  67   __asm__ __volatile__ ("lock; cmpxchgl %3, %1; sete %0"
  68                         : "=q" (ret), "=m" (*p), "=a" (readval)
  69                         : "r" (newval), "m" (*p), "a" (oldval)
  70                         : "memory");
  71   return ret;
  72 }
  73
  74
  75 PT_EI int
  76 get_eflags (void)
  77 {
  78   int res;
  79   __asm__ __volatile__ ("pushfl; popl %0" : "=r" (res) : );
  80   return res;
  81 }
  82
  83
  84 PT_EI void
  85 set_eflags (int newflags)
  86 {
  87   __asm__ __volatile__ ("pushl %0; popfl" : : "r" (newflags) : "cc");
  88 }
  89
  90
  91 PT_EI int
  92 compare_and_swap_is_available (void)
  93 {
  94   int oldflags = get_eflags ();
  95   int changed;
  96   /* Flip AC bit in EFLAGS.  */
  97   set_eflags (oldflags ^ 0x40000);
  98   /* See if bit changed.  */
  99   changed = (get_eflags () ^ oldflags) & 0x40000;
 100   /* Restore EFLAGS.  */
 101   set_eflags (oldflags);
 102   /* If the AC flag did not change, it's a 386 and it lacks cmpxchg.
 103      Otherwise, it's a 486 or above and it has cmpxchg.  */
 104   return changed != 0;
 105 }
 106 #endif /* __ASSEMBLER__ */
 107
 108 #endif /* pt-machine.h */