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>
