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Annotation of embedaddon/nginx/src/os/unix/ngx_gcc_atomic_x86.h, revision 1.1

1.1     ! misho       1: 
        !             2: /*
        !             3:  * Copyright (C) Igor Sysoev
        !             4:  * Copyright (C) Nginx, Inc.
        !             5:  */
        !             6: 
        !             7: 
        !             8: #if (NGX_SMP)
        !             9: #define NGX_SMP_LOCK  "lock;"
        !            10: #else
        !            11: #define NGX_SMP_LOCK
        !            12: #endif
        !            13: 
        !            14: 
        !            15: /*
        !            16:  * "cmpxchgl  r, [m]":
        !            17:  *
        !            18:  *     if (eax == [m]) {
        !            19:  *         zf = 1;
        !            20:  *         [m] = r;
        !            21:  *     } else {
        !            22:  *         zf = 0;
        !            23:  *         eax = [m];
        !            24:  *     }
        !            25:  *
        !            26:  *
        !            27:  * The "r" means the general register.
        !            28:  * The "=a" and "a" are the %eax register.
        !            29:  * Although we can return result in any register, we use "a" because it is
        !            30:  * used in cmpxchgl anyway.  The result is actually in %al but not in %eax,
        !            31:  * however, as the code is inlined gcc can test %al as well as %eax,
        !            32:  * and icc adds "movzbl %al, %eax" by itself.
        !            33:  *
        !            34:  * The "cc" means that flags were changed.
        !            35:  */
        !            36: 
        !            37: static ngx_inline ngx_atomic_uint_t
        !            38: ngx_atomic_cmp_set(ngx_atomic_t *lock, ngx_atomic_uint_t old,
        !            39:     ngx_atomic_uint_t set)
        !            40: {
        !            41:     u_char  res;
        !            42: 
        !            43:     __asm__ volatile (
        !            44: 
        !            45:          NGX_SMP_LOCK
        !            46:     "    cmpxchgl  %3, %1;   "
        !            47:     "    sete      %0;       "
        !            48: 
        !            49:     : "=a" (res) : "m" (*lock), "a" (old), "r" (set) : "cc", "memory");
        !            50: 
        !            51:     return res;
        !            52: }
        !            53: 
        !            54: 
        !            55: /*
        !            56:  * "xaddl  r, [m]":
        !            57:  *
        !            58:  *     temp = [m];
        !            59:  *     [m] += r;
        !            60:  *     r = temp;
        !            61:  *
        !            62:  *
        !            63:  * The "+r" means the general register.
        !            64:  * The "cc" means that flags were changed.
        !            65:  */
        !            66: 
        !            67: 
        !            68: #if !(( __GNUC__ == 2 && __GNUC_MINOR__ <= 7 ) || ( __INTEL_COMPILER >= 800 ))
        !            69: 
        !            70: /*
        !            71:  * icc 8.1 and 9.0 compile broken code with -march=pentium4 option:
        !            72:  * ngx_atomic_fetch_add() always return the input "add" value,
        !            73:  * so we use the gcc 2.7 version.
        !            74:  *
        !            75:  * icc 8.1 and 9.0 with -march=pentiumpro option or icc 7.1 compile
        !            76:  * correct code.
        !            77:  */
        !            78: 
        !            79: static ngx_inline ngx_atomic_int_t
        !            80: ngx_atomic_fetch_add(ngx_atomic_t *value, ngx_atomic_int_t add)
        !            81: {
        !            82:     __asm__ volatile (
        !            83: 
        !            84:          NGX_SMP_LOCK
        !            85:     "    xaddl  %0, %1;   "
        !            86: 
        !            87:     : "+r" (add) : "m" (*value) : "cc", "memory");
        !            88: 
        !            89:     return add;
        !            90: }
        !            91: 
        !            92: 
        !            93: #else
        !            94: 
        !            95: /*
        !            96:  * gcc 2.7 does not support "+r", so we have to use the fixed
        !            97:  * %eax ("=a" and "a") and this adds two superfluous instructions in the end
        !            98:  * of code, something like this: "mov %eax, %edx / mov %edx, %eax".
        !            99:  */
        !           100: 
        !           101: static ngx_inline ngx_atomic_int_t
        !           102: ngx_atomic_fetch_add(ngx_atomic_t *value, ngx_atomic_int_t add)
        !           103: {
        !           104:     ngx_atomic_uint_t  old;
        !           105: 
        !           106:     __asm__ volatile (
        !           107: 
        !           108:          NGX_SMP_LOCK
        !           109:     "    xaddl  %2, %1;   "
        !           110: 
        !           111:     : "=a" (old) : "m" (*value), "a" (add) : "cc", "memory");
        !           112: 
        !           113:     return old;
        !           114: }
        !           115: 
        !           116: #endif
        !           117: 
        !           118: 
        !           119: /*
        !           120:  * on x86 the write operations go in a program order, so we need only
        !           121:  * to disable the gcc reorder optimizations
        !           122:  */
        !           123: 
        !           124: #define ngx_memory_barrier()    __asm__ volatile ("" ::: "memory")
        !           125: 
        !           126: /* old "as" does not support "pause" opcode */
        !           127: #define ngx_cpu_pause()         __asm__ (".byte 0xf3, 0x90")