Parsing process Analysis of the "PHP kernel learning" Global keyword

This article GitHub address:

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

|=-----------------------------------------------------------------------=|| =--------------------parsing Process Analysis of =[global keywords]=-------------------=| | =-----------------------------------------------------------------------=|| =--------------------------=[by D4shman]=---------------------------=| | =-----------------------------------------------------------------------=|| =-------------------------=[May 8,]=---------------------------=| | =-----------------------------------------------------------------------=|
[Catalogue]0x01 Lexical Analysis 0X02 Syntax Analysis 0x03 explanation implementation 0x04 Reference
0x01 Lexical analysis
[Email protected]# vi/php-dev/php-5.4.8/zend/zend_language_scanner.l Find Global:
<ST_IN_SCRIPTING> "Global" {return t_global; } found returning a token T_global
0X02 Syntax Analysis
By token T_global come to zend_language_parser.y find: | T_global global_var_list '; '
Global_var_list:global_var_list ', ' Global_var {zend_do_fetch_global_variable (&$3, NULL, ZEND_FETCH_GLOB Al_lock tsrmls_cc);   }        |    Global_var {zend_do_fetch_global_variable (&$1, NULL, Zend_fetch_global_lock tsrmls_cc);} The above refers to the global_val, as you can see, for global variables, the parser calls the Zend_do_fetch_globa_variable function of the Zend engine. The declaration of this function is zend/zend_compile.c
0X03 Interpreting execution
Find the Zend_do_fetch_global_variable function definition in zend/zend_compile.c:
void Zend_do_fetch_global_variable (Znode *varname, const znode *static_assignment, int fetch_type TSRMLS_DC) {        Zend_op *opline;        Znode lval; Znode result;
/* If the variable type is constant and not a string, it is converted to a string type */        if (Varname->op_type = = Is_ CONST) {            if (Z_type (varname-> u.constant)! = is_string) {                 convert_to_string (&varname->u.constant);             }        }             opline = Get_next_op (CG (Active_op_array) tsrmls_cc);      /* Cg:compile_global */        opline->opcode = ZEND_FETCH_W; /* The default mode must be write */        opline->result_type = is_var;         opline->result.var = get_temporary_variable (CG (active_op_array));        &nbsp Set_node (OPLINE-&GT;OP1, varname);         if (Opline->op1_type = IS_ CONST) {            calculate_literal_hash (opline- >op1.constant);        }         set_unused (OPLINE-&GT;OP2);         opline->extended_value = Fetch_type;        get_node (&result, Opline->result);             if (Varname->op_type = = IS_CONST) {             zval_copy_ctor (&varname->u.constant);         }/* relies on the fact, the default fetch is Bp_var_w */  & Nbsp;     fetch_simple_variable (&lval, varname, 0 tsrmls_cc);              zend_do_assign_ref (NULL, &lval, &result TSRMLS_CC) ; &NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;CG (Active_op_array)-&GT;OPCODES[CG (Active_op_array), Last-1].result_type |= ext_type_unused;    }
The code above confirms that opcode is zend_fetch_w and executes the ZEND_DO_ASSIGN_REF function. There is such a key statement in the ZEND_DO_ASSIGN_REF function:
Opline->opcode = Zend_assign_ref;
So, in the process of parsing, 2 opcode:zend_fetch_w and zend_assign_ref are actually executed, and the corresponding opcode are 83 and 39 respectively in Zend_vm_opcodes.h. The method to calculate the last call is (defined in zend_execute.c:):
Zend_opcode_handlers[opcode * + Zend_vm_decode[op->op1.op_type] * 5 + zend_vm_decode[op->op2.op_type]];
After the calculation (///////////I did not figure out how to calculate the//////////), the function that gets called is:
static int Zend_fastcall Zend_fetch_w_spec_cv_handler (Zend_opcode_handler_args) {return zend_fetch_var_address    _HELPER_SPEC_CV (Bp_var_w, Zend_opcode_handler_args_passthru); }
In ZEND_FETCH_VAR_ADDRESS_HELPER_SPEC_CV, call the following code to get the symbol table:
target_symbol_table = zend_get_target_symbol_table (Opline, EX (Ts), type, varname tsrmls_cc);
The implementation of the Zend_get_target_symbol_table function is as follows (in):
    static inline HashTable *zend_get_target_symbol_table (int fetch_type tsrmls_dc)      {        switch (Fetch_type) {             case zend_fetch_local:                  if (! EG (active_symbol_table)) {                     zend_rebuild_symbol_table (Tsrmls_c);                 }                 return EG (active_symbol_table);                 break;             case ZEND_FETCH_GLOBAL:&NBSp;           case zend_fetch_global_lock:                 return &EG (symbol_table ); /* Returns the address of the global variable symbol table */                 break;            case ZEND_FETCH_STATIC:                 if (! EG (Active_op_array)->static_variables) {                     alloc_hashtable (EG (Active_op_array)->static_variables );                     zend_hash_init (EG (Active_op_array)->static_variables, 2, NULL, Zval_ptr_dtor, 0);                 }                 return EG (Active_op_array)->static_variables;                 break;             empty_switch_default_case ()          }        return NULL;     }
The code can see that the function uses the EG (EXCUTOR_GLOBAL) macro to return the symbol table address of the GLOBAL variable when the passed Fetch_type is Zend_fetch_global (_lock).
The above is the whole process of the global variable parsing execution.
0X04 Reference Documents
In-depth understanding of the PHP kernel