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   1 /* include/asm-i386/rwlock.h
   2  *
   3  *      Helpers used by both rw spinlocks and rw semaphores.
   4  *
   5  *      Based in part on code from semaphore.h and
   6  *      spinlock.h Copyright 1996 Linus Torvalds.
   7  *
   8  *      Copyright 1999 Red Hat, Inc.
   9  *
  10  *      Written by Benjamin LaHaise.
  11  *
  12  *      This program is free software; you can redistribute it and/or
  13  *      modify it under the terms of the GNU General Public License
  14  *      as published by the Free Software Foundation; either version
  15  *      2 of the License, or (at your option) any later version.
  16  */
  17 #ifndef _ASM_I386_RWLOCK_H
  18 #define _ASM_I386_RWLOCK_H
  19
  20 #define RW_LOCK_BIAS             0x01000000
  21 #define RW_LOCK_BIAS_STR        "0x01000000"
  22
  23 #define __build_read_lock_ptr(rw, helper)   \
  24         asm volatile(LOCK "subl $1,(%0)\n\t" \
  25                      "jns 1f\n" \
  26                      "call " helper "\n\t" \
  27                      "1:\n" \
  28                      ::"a" (rw) : "memory")
  29
  30 #define __build_read_lock_const(rw, helper)   \
  31         asm volatile(LOCK "subl $1,%0\n\t" \
  32                      "jns 1f\n" \
  33                      "pushl %%eax\n\t" \
  34                      "leal %0,%%eax\n\t" \
  35                      "call " helper "\n\t" \
  36                      "popl %%eax\n\t" \
  37                      "1:\n" \
  38                      :"=m" (*(volatile int *)rw) : : "memory")
  39
  40 #define __build_read_lock(rw, helper)   do { \
  41                                                 if (__builtin_constant_p(rw)) \
  42                                                         __build_read_lock_const(rw, helper); \
  43                                                 else \
  44                                                         __build_read_lock_ptr(rw, helper); \
  45                                         } while (0)
  46
  47 #define __build_write_lock_ptr(rw, helper) \
  48         asm volatile(LOCK "subl $" RW_LOCK_BIAS_STR ",(%0)\n\t" \
  49                      "jz 1f\n" \
  50                      "call " helper "\n\t" \
  51                      "1:\n" \
  52                      ::"a" (rw) : "memory")
  53
  54 #define __build_write_lock_const(rw, helper) \
  55         asm volatile(LOCK "subl $" RW_LOCK_BIAS_STR ",%0\n\t" \
  56                      "jz 1f\n" \
  57                      "pushl %%eax\n\t" \
  58                      "leal %0,%%eax\n\t" \
  59                      "call " helper "\n\t" \
  60                      "popl %%eax\n\t" \
  61                      "1:\n" \
  62                      :"=m" (*(volatile int *)rw) : : "memory")
  63
  64 #define __build_write_lock(rw, helper)  do { \
  65                                                 if (__builtin_constant_p(rw)) \
  66                                                         __build_write_lock_const(rw, helper); \
  67                                                 else \
  68                                                         __build_write_lock_ptr(rw, helper); \
  69                                         } while (0)
  70
  71 #endif