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   1 /* include/asm-x86_64/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  *      Copyright 2001,2002 SuSE labs
  10  *
  11  *      Written by Benjamin LaHaise.
  12  *
  13  *      This program is free software; you can redistribute it and/or
  14  *      modify it under the terms of the GNU General Public License
  15  *      as published by the Free Software Foundation; either version
  16  *      2 of the License, or (at your option) any later version.
  17  */
  18 #ifndef _ASM_X86_64_RWLOCK_H
  19 #define _ASM_X86_64_RWLOCK_H
  20
  21 #include <linux/stringify.h>
  22
  23 #define RW_LOCK_BIAS             0x01000000
  24 #define RW_LOCK_BIAS_STR        "0x01000000"
  25
  26 #define __build_read_lock_ptr(rw, helper)   \
  27         asm volatile(LOCK "subl $1,(%0)\n\t" \
  28                      "js 2f\n" \
  29                      "1:\n" \
  30                     LOCK_SECTION_START("") \
  31                      "2:\tcall " helper "\n\t" \
  32                      "jmp 1b\n" \
  33                     LOCK_SECTION_END \
  34                      ::"a" (rw) : "memory")
  35
  36 #define __build_read_lock_const(rw, helper)   \
  37         asm volatile(LOCK "subl $1,%0\n\t" \
  38                      "js 2f\n" \
  39                      "1:\n" \
  40                     LOCK_SECTION_START("") \
  41                      "2:\tpushq %%rax\n\t" \
  42                      "leaq %0,%%rax\n\t" \
  43                      "call " helper "\n\t" \
  44                      "popq %%rax\n\t" \
  45                      "jmp 1b\n" \
  46                     LOCK_SECTION_END \
  47                      :"=m" (*((volatile int *)rw))::"memory")
  48
  49 #define __build_read_lock(rw, helper)   do { \
  50                                                 if (__builtin_constant_p(rw)) \
  51                                                         __build_read_lock_const(rw, helper); \
  52                                                 else \
  53                                                         __build_read_lock_ptr(rw, helper); \
  54                                         } while (0)
  55
  56 #define __build_write_lock_ptr(rw, helper) \
  57         asm volatile(LOCK "subl $" RW_LOCK_BIAS_STR ",(%0)\n\t" \
  58                      "jnz 2f\n" \
  59                      "1:\n" \
  60                      LOCK_SECTION_START("") \
  61                      "2:\tcall " helper "\n\t" \
  62                      "jmp 1b\n" \
  63                      LOCK_SECTION_END \
  64                      ::"a" (rw) : "memory")
  65
  66 #define __build_write_lock_const(rw, helper) \
  67         asm volatile(LOCK "subl $" RW_LOCK_BIAS_STR ",(%0)\n\t" \
  68                      "jnz 2f\n" \
  69                      "1:\n" \
  70                     LOCK_SECTION_START("") \
  71                      "2:\tpushq %%rax\n\t" \
  72                      "leaq %0,%%rax\n\t" \
  73                      "call " helper "\n\t" \
  74                      "popq %%rax\n\t" \
  75                      "jmp 1b\n" \
  76                     LOCK_SECTION_END \
  77                      :"=m" (*((volatile long *)rw))::"memory")
  78
  79 #define __build_write_lock(rw, helper)  do { \
  80                                                 if (__builtin_constant_p(rw)) \
  81                                                         __build_write_lock_const(rw, helper); \
  82                                                 else \
  83                                                         __build_write_lock_ptr(rw, helper); \
  84                                         } while (0)
  85
  86 #endif