【PHP内核学习】global关键字的解析过程分析

本文github地址：

https://github.com/wusuopubupt/phpLib/blob/master/global%E5%85%B3%E9%94%AE%E5%AD%97%E7%9A%84%E8%A7%A3%E6%9E%90%E8%BF%87%E7%A8%8B%E5%88%86%E6%9E%90

          <p class="sycode">              |=-----------------------------------------------------------------------=|          </p>          <p class="sycode">              |=--------------------=[ global关键字的解析过程分析 ]=-------------------=|          </p>          <p class="sycode">              |=-----------------------------------------------------------------------=|          </p>          <p class="sycode">              |=--------------------------=[  by d4shman  ]=---------------------------=|          </p>          <p class="sycode">              |=-----------------------------------------------------------------------=|          </p>          <p class="sycode">              |=-------------------------=[  May 8, 2014  ]=---------------------------=|          </p>          <p class="sycode">              |=-----------------------------------------------------------------------=|          </p>          <p class="sycode">              <br>          </p>          <p class="sycode">              [目录]          </p>          <p class="sycode">              0x01 词法分析           </p>          <p class="sycode">              0X02 语法分析          </p>          <p class="sycode">              0X03 解释执行          </p>          <p class="sycode">              0X04 参考文献          </p>          <p class="sycode">              <br>          </p>          <p class="sycode">              0x01 词法分析          </p>          <p class="sycode">              <br>          </p>          <p class="sycode">              d4shman@gentoo# vi /php-dev/php-5.4.8/Zend/zend_language_scanner.l          </p>          <p class="sycode">              找到global：          </p>          <p class="sycode">              <br>          </p>          <p class="sycode">                  <st_in_scripting>"global" {          </st_in_scripting></p>          <p class="sycode">                      return T_GLOBAl;          </p>          <p class="sycode">                  }          </p>          <p class="sycode">              发现返回一个token T_GLOBAL          </p>          <p class="sycode">              <br>          </p>          <p class="sycode">              0X02 语法分析          </p>          <p class="sycode">              <br>          </p>          <p class="sycode">              通过token T_GLOBAL来到zend_language_parser.y找到：          </p>          <p class="sycode">                  |   T_GLOBAL global_var_list ';'          </p>          <p class="sycode">              <br>          </p>          <p class="sycode">                  global_var_list:          </p>          <p class="sycode">                          global_var_list ',' global_var  { zend_do_fetch_global_variable(&$3, NULL, ZEND_FETCH_GLOBAL_LOCK TSRMLS_CC); }          </p>          <p class="sycode">                      |   global_var                      { zend_do_fetch_global_variable(&$1, NULL, ZEND_FETCH_GLOBAL_LOCK TSRMLS_CC); }          </p>          <p class="sycode">                  ;          </p>          <p class="sycode">              上面的$3指的是global_val，可以看到，对于全局变量，语法分析器调用的是Zend引擎          </p>          <p class="sycode">              的zend_do_fetch_globa_variable函数。此函数的声明在Zend/zend_compile.c          </p>          <p class="sycode">              <br>          </p>          <p class="sycode">              0X03 解释执行          </p>          <p class="sycode">              <br>          </p>          <p class="sycode">                  在Zend/zend_compile.c中找到zend_do_fetch_global_variable函数定义：          </p>          <p class="sycode">              <br>          </p>          <p class="sycode">                  void zend_do_fetch_global_variable(znode *varname, const znode *static_assignment, int fetch_type TSRMLS_DC)           </p>          <p class="sycode">                  {          </p>          <p class="sycode">                      zend_op *opline;          </p>          <p class="sycode">                      znode lval;          </p>          <p class="sycode">                      znode result;          </p>          <p class="sycode">              <br>          </p>          <p class="sycode">              		/*如果变量类型是常量且不是字符串，则将其转化成字符串类型*/          </p>          <p class="sycode">                      if (varname->op_type == IS_CONST) {            </p>          <p class="sycode">                          if (Z_TYPE(varname->u.constant) != IS_STRING) {          </p>          <p class="sycode">                              convert_to_string(&varname->u.constant);          </p>          <p class="sycode">                          }          </p>          <p class="sycode">                      }          </p>          <p class="sycode">                            </p>          <p class="sycode">                      opline = get_next_op(CG(active_op_array) TSRMLS_CC); /* CG: compile_global */          </p>          <p class="sycode">                      opline->opcode = ZEND_FETCH_W;      /* 默认的模式必须是Write */          </p>          <p class="sycode">                      opline->result_type = IS_VAR;          </p>          <p class="sycode">                      opline->result.var = get_temporary_variable(CG(active_op_array));          </p>          <p class="sycode">                      SET_NODE(opline->op1, varname);          </p>          <p class="sycode">                      if (opline->op1_type == IS_CONST) {          </p>          <p class="sycode">                          CALCULATE_LITERAL_HASH(opline->op1.constant);          </p>          <p class="sycode">                      }          </p>          <p class="sycode">                      SET_UNUSED(opline->op2);          </p>          <p class="sycode">                      opline->extended_value = fetch_type;          </p>          <p class="sycode">                      GET_NODE(&result, opline->result);          </p>          <p class="sycode">                            </p>          <p class="sycode">                      if (varname->op_type == IS_CONST) {          </p>          <p class="sycode">                          zval_copy_ctor(&varname->u.constant);          </p>          <p class="sycode">                      }          </p>          <p class="sycode">              		/* Relies on the fact that the default fetch is BP_VAR_W */          </p>          <p class="sycode">                      fetch_simple_variable(&lval, varname, 0 TSRMLS_CC);           </p>          <p class="sycode">                            </p>          <p class="sycode">                      zend_do_assign_ref(NULL, &lval, &result TSRMLS_CC);          </p>          <p class="sycode">                      CG(active_op_array)->opcodes[CG(active_op_array)->last-1].result_type |= EXT_TYPE_UNUSED;          </p>          <p class="sycode">                  }          </p>          <p class="sycode">              <br>          </p>          <p class="sycode">                  上面的代码确认了opcode为ZEND_FETCH_W外，还执行了zend_do_assign_ref函数。zend_do_assign_ref函数中          </p>          <p class="sycode">              有这么一个关键语句：          </p>          <p class="sycode">              <br>          </p>          <p class="sycode">                  opline->opcode = ZEND_ASSIGN_REF;          </p>          <p class="sycode">              <br>          </p>          <p class="sycode">                  由此可知，语法分析过程中，实际执行了2个opcode: ZEND_FETCH_W和ZEND_ASSIGN_REF，在zend_vm_opcodes.h          </p>          <p class="sycode">              中发现，它们对应的opcode分别是83和39。而计算最后调用的方法是(定义在zend_execute.c:)：          </p>          <p class="sycode">              <br>          </p>          <p class="sycode">                  zend_opcode_handlers[opcode * 25 + zend_vm_decode[op->op1.op_type] * 5 + zend_vm_decode[op->op2.op_type]];          </p>          <p class="sycode">              <br>          </p>          <p class="sycode">                  计算后（///////////我没搞清楚是怎么计算出的//////////）,得到调用的函数是：          </p>          <p class="sycode">              <br>          </p>          <p class="sycode">                  static int ZEND_FASTCALL  ZEND_FETCH_W_SPEC_CV_HANDLER(ZEND_OPCODE_HANDLER_ARGS)          </p>          <p class="sycode">                  {          </p>          <p class="sycode">                      return zend_fetch_var_address_helper_SPEC_CV(BP_VAR_W, ZEND_OPCODE_HANDLER_ARGS_PASSTHRU);          </p>          <p class="sycode">                  }	          </p>          <p class="sycode">              <br>          </p>          <p class="sycode">                  在zend_fetch_var_address_helper_SPEC_CV中调用如下代码获取符号表：          </p>          <p class="sycode">              <br>          </p>          <p class="sycode">                  target_symbol_table = zend_get_target_symbol_table(opline, EX(Ts), type, varname TSRMLS_CC);          </p>          <p class="sycode">              <br>          </p>          <p class="sycode">              	zend_get_target_symbol_table函数的实现如下（在）：          </p>          <p class="sycode">              <br>          </p>          <p class="sycode">                  static inline HashTable *zend_get_target_symbol_table(int fetch_type TSRMLS_DC)          </p>          <p class="sycode">                  {          </p>          <p class="sycode">                      switch (fetch_type) {          </p>          <p class="sycode">                          case ZEND_FETCH_LOCAL:            </p>          <p class="sycode">                              if (!EG(active_symbol_table)) {          </p>          <p class="sycode">                                  zend_rebuild_symbol_table(TSRMLS_C);          </p>          <p class="sycode">                              }          </p>          <p class="sycode">                              return EG(active_symbol_table);          </p>          <p class="sycode">                              break;          </p>          <p class="sycode">                          case ZEND_FETCH_GLOBAL:          </p>          <p class="sycode">                          case ZEND_FETCH_GLOBAL_LOCK:          </p>          <p class="sycode">                              return &EG(symbol_table); /*返回global 变量符号表的地址*/          </p>          <p class="sycode">                              break;          </p>          <p class="sycode">                          case ZEND_FETCH_STATIC:          </p>          <p class="sycode">                              if (!EG(active_op_array)->static_variables) {          </p>          <p class="sycode">                                  ALLOC_HASHTABLE(EG(active_op_array)->static_variables);          </p>          <p class="sycode">                                  zend_hash_init(EG(active_op_array)->static_variables, 2, NULL, ZVAL_PTR_DTOR, 0);          </p>          <p class="sycode">                              }          </p>          <p class="sycode">                              return EG(active_op_array)->static_variables;          </p>          <p class="sycode">                              break;          </p>          <p class="sycode">                          EMPTY_SWITCH_DEFAULT_CASE()          </p>          <p class="sycode">                      }          </p>          <p class="sycode">                      return NULL;          </p>          <p class="sycode">                  }          </p>          <p class="sycode">              <br>          </p>          <p class="sycode">              	通过代码可以看到，当传递过来的fetch_type是ZEND_FETCH_GLOBAL(_LOCK)时，函数使用EG(excutor_global)宏          </p>          <p class="sycode">              返回了global变量的符号表地址。          </p>          <p class="sycode">              <br>          </p>          <p class="sycode">                  以上就是global变量解析执行的整个过程。          </p>          <p class="sycode">              <br>          </p>          <p class="sycode">              0X04 参考文献          </p>          <p class="sycode">              <br>          </p>          <p class="sycode">              《深入理解PHP内核》          </p>          <p class="sycode">              <br>          </p>          <p class="sycode">              <br>          </p>          <p class="sycode">              <br>          </p>          <p class="sycode">              <br>          </p>          <p class="sycode">                            </p>