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561
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1
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2 /*
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3 * Copyright (C) Igor Sysoev
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4 */
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5
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6
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7 #if (NGX_SMP)
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8 #define NGX_SMP_LOCK "lock;"
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9 #else
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10 #define NGX_SMP_LOCK
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11 #endif
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12
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13
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14 /*
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15 * "cmpxchgl r, [m]":
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16 *
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17 * if (eax == [m]) {
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18 * zf = 1;
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19 * [m] = r;
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20 * } else {
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21 * zf = 0;
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22 * eax = [m];
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23 * }
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24 *
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577
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25 *
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561
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26 * The "q" is any of the %eax, %ebx, %ecx, or %edx registers.
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27 * The "=a" and "a" are the %eax register. Although we can return result
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28 * in any register, we use %eax because it is used in cmpxchgl anyway.
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29 * The "cc" means that flags were changed.
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30 */
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31
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32 static ngx_inline ngx_atomic_uint_t
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33 ngx_atomic_cmp_set(ngx_atomic_t *lock, ngx_atomic_uint_t old,
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34 ngx_atomic_uint_t set)
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35 {
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36 ngx_atomic_uint_t res;
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37
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38 __asm__ volatile (
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39
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40 NGX_SMP_LOCK
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41 " cmpxchgl %3, %1; "
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42 " setz %b0; "
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43 " movzbl %b0, %0; "
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44
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45 : "=a" (res) : "m" (*lock), "a" (old), "q" (set) : "cc", "memory");
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46
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47 return res;
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48 }
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49
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50
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51 /*
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52 * "xaddl r, [m]":
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53 *
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54 * temp = [m];
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55 * [m] += r;
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56 * r = temp;
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57 *
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58 *
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59 * The "+q" is any of the %eax, %ebx, %ecx, or %edx registers.
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60 * The "cc" means that flags were changed.
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61 */
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62
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63
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589
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64 #if !(( __GNUC__ == 2 && __GNUC_MINOR__ <= 7 ) || ( __INTEL_COMPILER >= 800 ))
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65
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66 /*
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67 * icc 8.1 and 9.0 compile broken code with -march=pentium4 option:
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68 * ngx_atomic_fetch_add() always return the input "add" value,
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69 * so we use the gcc 2.7 version.
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70 *
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71 * icc 8.1 and 9.0 with -march=pentiumpro option or icc 7.1 compile
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72 * correct code.
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73 */
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561
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74
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75 static ngx_inline ngx_atomic_int_t
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76 ngx_atomic_fetch_add(ngx_atomic_t *value, ngx_atomic_int_t add)
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77 {
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78 __asm__ volatile (
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79
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80 NGX_SMP_LOCK
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81 " xaddl %0, %1; "
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82
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83 : "+q" (add) : "m" (*value) : "cc", "memory");
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84
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85 return add;
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86 }
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87
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88
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589
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89 #else
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561
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90
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91 /*
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92 * gcc 2.7 does not support "+q", so we have to use the fixed %eax ("=a" and
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93 * "a") and this adds two superfluous instructions in the end of code,
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94 * something like this: "mov %eax, %edx / mov %edx, %eax".
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95 */
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96
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97 static ngx_inline ngx_atomic_int_t
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98 ngx_atomic_fetch_add(ngx_atomic_t *value, ngx_atomic_int_t add)
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99 {
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100 ngx_atomic_uint_t old;
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101
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102 __asm__ volatile (
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103
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104 NGX_SMP_LOCK
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105 " xaddl %2, %1; "
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106
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107 : "=a" (old) : "m" (*value), "a" (add) : "cc", "memory");
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108
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109 return old;
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110 }
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111
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112 #endif
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563
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113
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114
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115 /*
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116 * on x86 the write operations go in a program order, so we need only
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117 * to disable the gcc reorder optimizations
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118 */
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119
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120 #define ngx_memory_barrier() __asm__ volatile ("" ::: "memory")
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611
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121
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122 /* old as does not support "pause" opcode */
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123 #define ngx_cpu_pause() __asm__ (".byte 0xf3, 0x90")
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