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php 连接字符串. ZEND_ASSIGN_CONCAT/ZEND_CONCAT原理
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0.php代码
<?php
$a='abc';
$b='def';
$c='ghi';
$d='jkl';
$a.=$b.$c.$d;
1.BNF范式（语法规则）
expr_without_variable:
| variable T_CONCAT_EQUAL expr { zend_check_writable_variable(&$); zend_do_end_variable_parse(&$, BP_VAR_RW, TSRMLS_CC); zend_do_binary_assign_op(ZEND_ASSIGN_CONCAT, &$$, &$, &$ TSRMLS_CC); } | expr '.' expr { zend_do_binary_op(ZEND_CONCAT, &$$, &$, &$ TSRMLS_CC); }
2.生成opcode
void zend_do_binary_assign_op(zend_uchar op, znode *result, const znode *op1, const znode *op2 TSRMLS_DC) /* {{{ */
{
int last_op_number = get_next_op_number(CG(active_op_array));
zend_op *opline = get_next_op(CG(active_op_array) TSRMLS_CC);
if (last_op_number > ) { //这一段不知道什么意思
zend_op *last_op = &CG(active_op_array)->opcodes[last_op_number-];
switch (last_op->opcode) {
case ZEND_FETCH_OBJ_RW:
last_op->opcode = op;
last_op->extended_value = ZEND_ASSIGN_OBJ;
zend_do_op_data(opline, op2 TSRMLS_CC);
SET_UNUSED(opline->result);
GET_NODE(result, last_op->result);
return;
case ZEND_FETCH_DIM_RW:
last_op->opcode = op;
last_op->extended_value = ZEND_ASSIGN_DIM;
zend_do_op_data(opline, op2 TSRMLS_CC);
opline->op2.var = get_temporary_variable(CG(active_op_array));
opline->op2_type = IS_VAR;
SET_UNUSED(opline->result);
GET_NODE(result,last_op->result);
return;
default:
break;
}
}
opline->opcode = op;
SET_NODE(opline->op1, op1);
SET_NODE(opline->op2, op2);
opline->result_type = IS_VAR;
opline->result.var = get_temporary_variable(CG(active_op_array));
GET_NODE(result, opline->result);
}
#define SET_NODE(target, src) do { \
target ## _type = (src)->op_type; \
if ((src)->op_type == IS_CONST) { \
target.constant = zend_add_literal(CG(active_op_array), &(src)->u.constant TSRMLS_CC); \
} else { \
target = (src)->u.op; \
} \
} while ()
3.执行opcode
static int ZEND_FASTCALL ZEND_ASSIGN_CONCAT_SPEC_CV_TMP_HANDLER(ZEND_OPCODE_HANDLER_ARGS)
{
return zend_binary_assign_op_helper_SPEC_CV_TMP(concat_function, ZEND_OPCODE_HANDLER_ARGS_PASSTHRU);
} static int ZEND_FASTCALL zend_binary_assign_op_helper_SPEC_CV_TMP(int (*binary_op)(zval *result, zval *op1, zval *op2 TSRMLS_DC), ZEND_OPCODE_HANDLER_ARGS)
{
USE_OPLINE
zend_free_op free_op2, free_op_data2, free_op_data1;
zval **var_ptr;
zval *value; SAVE_OPLINE();
switch (opline->extended_value) {
case ZEND_ASSIGN_OBJ:
..........break;
case ZEND_ASSIGN_DIM: {
.........
}
break;
default:
value = _get_zval_ptr_tmp(opline->op2.var, EX_Ts(), &free_op2 TSRMLS_CC);
var_ptr = _get_zval_ptr_ptr_cv_BP_VAR_RW(EX_CVs(), opline->op1.var TSRMLS_CC);
/* do nothing */
break;
} if (UNEXPECTED(var_ptr == NULL)) {
zend_error_noreturn(E_ERROR, "Cannot use assign-op operators with overloaded objects nor string offsets");
} if (UNEXPECTED(*var_ptr == &EG(error_zval))) {
...........
ZEND_VM_NEXT_OPCODE();
} SEPARATE_ZVAL_IF_NOT_REF(var_ptr); if (UNEXPECTED(Z_TYPE_PP(var_ptr) == IS_OBJECT)
&& Z_OBJ_HANDLER_PP(var_ptr, get)
&& Z_OBJ_HANDLER_PP(var_ptr, set)) {
/* proxy object */
//对象的操作
} else {
binary_op(*var_ptr, *var_ptr, value TSRMLS_CC);//故意设置第一个参数与第二个参数一样
} ...........
zval_dtor(free_op2.var);
...........
ZEND_VM_NEXT_OPCODE();
}
typedef int (*binary_op_type)(zval *, zval *, zval * TSRMLS_DC);
执行$a.$b时，执行concat_function,第一个参数为一个临时变量（类型为zval）, 执行函数后，这个临时变量即保存了concat后的字符串的首地址，然后这个临时变量会放到yyvsp这个数组里，当再移进.$c后，归约成exp.exp,取出这个临时变量作为函数concat_function的第二个参数，$c作为第三个参数 ， 执行concat_funcion,将第一个参数的值放回yyvsp
static int ZEND_FASTCALL ZEND_CONCAT_SPEC_CONST_CV_HANDLER(ZEND_OPCODE_HANDLER_ARGS)
{
USE_OPLINE SAVE_OPLINE();
concat_function(&EX_T(opline->result.var).tmp_var,
opline->op1.zv,
_get_zval_ptr_cv_BP_VAR_R(EX_CVs(), opline->op2.var TSRMLS_CC) TSRMLS_CC); CHECK_EXCEPTION();
ZEND_VM_NEXT_OPCODE();
}
ZEND_API int concat_function(zval *result, zval *op1, zval *op2 TSRMLS_DC) /* {{{ */
{
zval op1_copy, op2_copy;
int use_copy1 = , use_copy2 = ;
if (Z_TYPE_P(op1) != IS_STRING) {
zend_make_printable_zval(op1, &op1_copy, &use_copy1);
}
if (Z_TYPE_P(op2) != IS_STRING) {
zend_make_printable_zval(op2, &op2_copy, &use_copy2);
}
if (use_copy1) {
/* We have created a converted copy of op1. Therefore, op1 won't become the result so
* we have to free it.
*/
if (result == op1) {
zval_dtor(op1);
}
op1 = &op1_copy;
}
if (use_copy2) {
op2 = &op2_copy;
}
if (result==op1 && !IS_INTERNED(Z_STRVAL_P(op1))) { /* special case, perform operations on result */
uint res_len = Z_STRLEN_P(op1) + Z_STRLEN_P(op2);
if (Z_STRLEN_P(result) < || (int) (Z_STRLEN_P(op1) + Z_STRLEN_P(op2)) < ) {
efree(Z_STRVAL_P(result));
ZVAL_EMPTY_STRING(result);
zend_error(E_ERROR, "String size overflow");
}
Z_STRVAL_P(result) = erealloc(Z_STRVAL_P(result), res_len+1);//realloc在紧接原来内存后面，开僻一块内存，如果没有足够内存，重新找一块内存
memcpy(Z_STRVAL_P(result)+Z_STRLEN_P(result), Z_STRVAL_P(op2), Z_STRLEN_P(op2));
Z_STRVAL_P(result)[res_len]=;
Z_STRLEN_P(result) = res_len;
} else {
int length = Z_STRLEN_P(op1) + Z_STRLEN_P(op2);
char *buf = (char *) emalloc(length + );//重新malloc分配内存
memcpy(buf, Z_STRVAL_P(op1), Z_STRLEN_P(op1));
memcpy(buf + Z_STRLEN_P(op1), Z_STRVAL_P(op2), Z_STRLEN_P(op2));
buf[length] = ;
ZVAL_STRINGL(result, buf, length, );
}
if (use_copy1) {
zval_dtor(op1);
}
if (use_copy2) {
zval_dtor(op2);
}
return SUCCESS;
}
