php7 改为从栈上分配内在的思路

时间：2022-03-12 08:28:17

php7的特点是规则上不从堆上分配内存,改为从栈上分配内存,

因为有些场景是从堆上分配内在后,还要手动释放内存,利用栈分配内在快的特点,在有需要的时候,再在堆上分配内在

但是栈上分配的内存，不能返回，因为当函数运行完后，就退栈了，但可以将该内在地址传给别的函数

php7的hashTable中的Bucket中的zval不再是指针,而是直接存储zval

由于从php代码上不好分析，只要从扩展上分析

<?php

$a=array();

$a['name']='taek-007';

?>

///////////////////////////////////////////////////////////////////////

PHP_FUNCTION(confirm_variable_compiled)

{

    zval val;

    array_init(&val);

    add_assoc_string(&val, "name", "taek-007");

    RETURN_ZVAL(&val,,);

}

为了能在gdb调试中打开宏,在编译php之前,修改configure该文件,增加红色的字样

  if test "$PHP_DEBUG" = "yes"; then

     PHP_DEBUG=

     ZEND_DEBUG=yes

     CFLAGS=`echo "$CFLAGS" | $SED -e 's/-O[0-9s]*//g'`

     CXXFLAGS=`echo "$CXXFLAGS" | $SED -e 's/-O[0-9s]*//g'`

       if test "$GCC" = "yes" || test "$ICC" = "yes"; then

       CFLAGS="$CFLAGS -gdwarf-2 -g3  -O0"

直接上gdb调试吧

gdb /usr/local/php/bin/php

(gdb)
(gdb) source /home/source/php-7.0.2/.gdbinit

(gdb) break /home/source/php-7.0.2/ext/variable/variable.c:66
No source file named /home/source/php-7.0.2/ext/variable/variable.c.
Make breakpoint pending on future shared library load? (y or [n]) y

Breakpoint 1 (/home/source/php-7.0.2/ext/variable/variable.c:66) pending.
(gdb)

(gdb) run /home/debug_php/variable.php
Starting program: /usr/local/php/bin/php /home/debug_php/variable.php
[Thread debugging using libthread_db enabled]
[New Thread 0xb7f4e6c0 (LWP 3761)]

Breakpoint 1, zif_confirm_variable_compiled (execute_data=0xb7c15090,
return_value=0xb7c15060) at /home/source/php-7.0.2/ext/variable/variable.c:67
67 array_init(&val);

(gdb) n
68 add_assoc_string(&val, "name", "taek-007");
(gdb) s
add_assoc_string_ex (arg=0xbf80cddc, key=0x493a7c "name", key_len=4,
str=0x493a73 "taek-007") at /home/source/php-7.0.2/Zend/zend_API.c:1383
1383 ZVAL_STRING(&tmp, str);
(gdb) macro expand ZVAL_STRING(&tmp, str)
expands to: do { const char *_s = (str); do { do { zval *__z = (&tmp); zend_string *__s = (zend_string_init(_s, strlen(_s), 0)); (*(__z)).value.str = __s; (*(__z)).u1.type_info = (6 | (( (1<<2) | (1<<4)) << 8)); } while (0); } while (0); } while (0)

(gdb) p (char*)str
$4 = 0x493a73 "taek-007"

(gdb) s
zend_string_init (str=0xe22a73 "taek-007", len=8, persistent=0)
at /home/source/php-7.0.2/Zend/zend_string.h:157
157 zend_string *ret = zend_string_alloc(len, persistent);

(gdb) n
159 memcpy(ZSTR_VAL(ret), str, len);

(gdb) p ret
$39 = (zend_string *) 0xb7c58900  //可以发现从堆上分配内存给了ret

(gdb) n
160 ZSTR_VAL(ret)[len] = '\0';

(gdb) p (char *)ret.val
$47 = 0xb7c58910 "taek-007"

.... 一直n

1384 ret = zend_symtable_str_update(Z_ARRVAL_P(arg), key, key_len, &tmp);
(gdb) p tmp.value.str
$51 = (zend_string *) 0xb7c58900

(gdb) p tmp.value
$54 = {lval = -1211791104, dval = 1.8828939190657202e-307, counted = 0xb7c58900,
str = 0xb7c58900, arr = 0xb7c58900, obj = 0xb7c58900, res = 0xb7c58900,
ref = 0xb7c58900, ast = 0xb7c58900, zv = 0xb7c58900, ptr = 0xb7c58900,
ce = 0xb7c58900, func = 0xb7c58900, ww = {w1 = 3083176192, w2 = 4254880}} //由于value本身是个结构体,故其中每个元素的地址都是0xb7c58900

(gdb) s  //进入函数zend_symtable_str_update
zend_symtable_str_update (ht=0xb7c59300, str=0xe22a7c "name", len=4,
pData=0xbfd1d0c4) at /home/source/php-7.0.2/Zend/zend_hash.h:392
392 if (ZEND_HANDLE_NUMERIC_STR(str, len, idx)) {
(gdb)

(gdb) n
395 return zend_hash_str_update(ht, str, len, pData);
(gdb) s
_zend_hash_str_update (ht=0xb7c59300, str=0xe22a7c "name", len=4, pData=0xbfd1d0c4,
__zend_filename=0x895c438 "/home/source/php-7.0.2/Zend/zend_hash.h",
__zend_lineno=395) at /home/source/php-7.0.2/Zend/zend_hash.c:653
653 zend_string *key = zend_string_init(str, len, ht->u.flags & HASH_FLAG_PERSISTENT);

(gdb) n
654 zval *ret = _zend_hash_add_or_update_i(ht, key, pData, HASH_UPDATE ZEND_FILE_LINE_RELAY_CC);

(gdb) p (char*)key.val
$56 = 0xb7c58940 "name"

(gdb) p (char *)pData.value.str.val
$58 = 0xb7c58910 "taek-007"

(gdb) p pData.value.str
$60 = (zend_string *) 0xb7c58900

(gdb) s
_zend_hash_add_or_update_i (ht=0xb7c59300, key=0xb7c58930, pData=0xbfd1d0c4, flag=1,
__zend_filename=0x895c438 "/home/source/php-7.0.2/Zend/zend_hash.h",
__zend_lineno=395) at /home/source/php-7.0.2/Zend/zend_hash.c:559
559 IS_CONSISTENT(ht);
(gdb) n
562 if (UNEXPECTED(!(ht->u.flags & HASH_FLAG_INITIALIZED))) {
(gdb)
563 CHECK_INIT(ht, 0); //检查hashtable情况
(gdb) macro expand CHECK_INIT(ht, 0)
expands to: zend_hash_check_init(ht, 0)
(gdb) s
zend_hash_check_init (ht=0xb7c59300, packed=0)
at /home/source/php-7.0.2/Zend/zend_hash.c:162
162 if (UNEXPECTED(!((ht)->u.flags & HASH_FLAG_INITIALIZED))) {
(gdb) n
163 zend_hash_real_init_ex(ht, packed);

(gdb) s
zend_hash_check_init (ht=0xb7c59300, packed=0)
at /home/source/php-7.0.2/Zend/zend_hash.c:162
162 if (UNEXPECTED(!((ht)->u.flags & HASH_FLAG_INITIALIZED))) {
(gdb) n
163 zend_hash_real_init_ex(ht, packed);
(gdb) s
zend_hash_real_init_ex (ht=0xb7c59300, packed=0)
at /home/source/php-7.0.2/Zend/zend_hash.c:133
133 ZEND_ASSERT(!((ht)->u.flags & HASH_FLAG_INITIALIZED));
(gdb) n
134 if (packed) {
(gdb)
139 (ht)->nTableMask = -(ht)->nTableSize;
(gdb)
140 HT_SET_DATA_ADDR(ht, pemalloc(HT_SIZE(ht), (ht)->u.flags & HASH_FLAG_PERSISTENT));

(gdb) p packed
$61 = 0
(gdb) p ht->nTableSize
$62 = 8

(gdb) macro expand HT_SET_DATA_ADDR  //分配8个Bucket大小的内存,并将首地址赋给ht->arData
expands to: HT_SET_DATA_ADDR
(gdb) macro expand HT_SET_DATA_ADDR(ht, pemalloc(HT_SIZE(ht), (ht)->u.flags & HASH_FLAG_PERSISTENT));
expands to: do { (ht)->arData = (Bucket*)(((char*)((((ht)->u.flags & (1<<0))?__zend_malloc((((size_t)(((ht)->nTableSize)) * sizeof(Bucket)) + (((size_t)(uint32_t)-(int32_t)(((ht)->nTableMask))) * sizeof(uint32_t)))):_emalloc(((((size_t)(((ht)->nTableSize)) * sizeof(Bucket)) + (((size_t)(uint32_t)-(int32_t)(((ht)->nTableMask))) * sizeof(uint32_t)))) , __FILE__, __LINE__ , ((void *)0), 0)))) + (((size_t)(uint32_t)-(int32_t)((ht)->nTableMask)) * sizeof(uint32_t))); } while (0);

(gdb) n
141 (ht)->u.flags |= HASH_FLAG_INITIALIZED;
(gdb)
142 if (EXPECTED(ht->nTableMask == -8)) {
(gdb)
143 Bucket *arData = ht->arData;
(gdb)
145 HT_HASH_EX(arData, -8) = -1;
(gdb)
146 HT_HASH_EX(arData, -7) = -1;
(gdb)
147 HT_HASH_EX(arData, -6) = -1;
(gdb)
148 HT_HASH_EX(arData, -5) = -1;
(gdb)
149 HT_HASH_EX(arData, -4) = -1;
(gdb)
150 HT_HASH_EX(arData, -3) = -1;
(gdb)
151 HT_HASH_EX(arData, -2) = -1;
(gdb)
152 HT_HASH_EX(arData, -1) = -1;
(gdb)
157 }
(gdb)
zend_hash_check_init (ht=0xb7c59300, packed=0)
at /home/source/php-7.0.2/Zend/zend_hash.c:165
165 }
(gdb)
_zend_hash_add_or_update_i (ht=0xb7c59300, key=0xb7c58930, pData=0xbfd1d0c4, flag=1,
__zend_filename=0x895c438 "/home/source/php-7.0.2/Zend/zend_hash.h",
__zend_lineno=395) at /home/source/php-7.0.2/Zend/zend_hash.c:564
564 goto add_to_hash;
(gdb)
595 idx = ht->nNumUsed++;

(gdb) n
596 ht->nNumOfElements++;
(gdb) p ht->nNumUsed++
$64 = 2
(gdb) p idx
$65 = 1
(gdb) n
597 if (ht->nInternalPointer == HT_INVALID_IDX) {
(gdb)
598 ht->nInternalPointer = idx;
(gdb)
600 zend_hash_iterators_update(ht, HT_INVALID_IDX, idx);
(gdb)
601 p = ht->arData + idx;

$67 = (Bucket *) 0xb7c60620
(gdb) p ht->arData+1
$68 = (Bucket *) 0xb7c60638
(gdb) n
602 p->key = key;
(gdb) p p
$69 = (Bucket *) 0xb7c60638

(gdb) p idx
$70 = 1
(gdb) n
603 if (!ZSTR_IS_INTERNED(key)) {
(gdb)
604 zend_string_addref(key);
(gdb)
605 ht->u.flags &= ~HASH_FLAG_STATIC_KEYS;
(gdb)
606 zend_string_hash_val(key);
(gdb)
608 p->h = h = ZSTR_H(key);
(gdb)
609 ZVAL_COPY_VALUE(&p->val, pData); //(*(_z1)).value.counted = _gc; 将堆上的内存地址分配到了hashTable中的Bucket中的val中的value.str
(gdb) macro expand ZVAL_COPY_VALUE(&p->val, pData)
expands to: do { zval *_z1 = (&p->val); const zval *_z2 = (pData); zend_refcounted *_gc = (*(_z2)).value.counted; uint32_t _t = (*(_z2)).u1.type_info; do { uint32_t _w2 = _z2->value.ww.w2; (*(_z1)).value.counted = _gc; _z1->value.ww.w2 = _w2; (*(_z1)).u1.type_info = _t; } while (0); } while (0)
(gdb) p p->val
$71 = {value = {lval = 0, dval = 0, counted = 0x0, str = 0x0, arr = 0x0, obj = 0x0,
res = 0x0, ref = 0x0, ast = 0x0, zv = 0x0, ptr = 0x0, ce = 0x0, func = 0x0,
ww = {w1 = 0, w2 = 0}}, u1 = {v = {type = 0 '\0', type_flags = 0 '\0',
const_flags = 0 '\0', reserved = 0 '\0'}, type_info = 0}, u2 = {var_flags = 0,
next = 0, cache_slot = 0, lineno = 0, num_args = 0, fe_pos = 0, fe_iter_idx = 0}}
(gdb) p pData.value
$72 = {lval = -1211791104, dval = 1.8828939190657202e-307, counted = 0xb7c58900,
str = 0xb7c58900, arr = 0xb7c58900, obj = 0xb7c58900, res = 0xb7c58900,
ref = 0xb7c58900, ast = 0xb7c58900, zv = 0xb7c58900, ptr = 0xb7c58900,
ce = 0xb7c58900, func = 0xb7c58900, ww = {w1 = 3083176192, w2 = 4254880}}
(gdb) p pData.value.counted
$73 = (zend_refcounted *) 0xb7c58900
(gdb) p (*(_z1)).value.counted
Cannot access memory at address 0x30
(gdb) p p->val.value.counted
$74 = (zend_refcounted *) 0x0
(gdb) p pData.u.type_info
There is no member named u.
(gdb) p pData.u1.type_info
$75 = 5126
(gdb) p p->val.value.u1.type_info
There is no member named u1.
(gdb) p p->val.u1.type_info
$76 = 0
(gdb) n
610 nIndex = h | ht->nTableMask;
(gdb) p p->val.value.counted
$77 = (zend_refcounted *) 0xb7c58900
(gdb) p p->val.value.u1.type_info
There is no member named u1.
(gdb) p p->val.u1.type_info
$78 = 5126
(gdb)

(gdb) n
610 nIndex = h | ht->nTableMask;
(gdb) p p->val.value.counted
$77 = (zend_refcounted *) 0xb7c58900
(gdb) p p->val.value.u1.type_info
There is no member named u1.
(gdb) p p->val.u1.type_info
$78 = 5126
(gdb) n
611 Z_NEXT(p->val) = HT_HASH(ht, nIndex);
(gdb) p HT_HASH(ht, nIndex);
Invalid character ';' in expression.
(gdb) n
612 HT_HASH(ht, nIndex) = HT_IDX_TO_HASH(idx);
(gdb) p HT_HASH(ht, nIndex)
$79 = 4294967295
(gdb) n
615 return &p->val;
(gdb) p HT_HASH(ht, nIndex)
$80 = 24
(gdb) p HT_IDX_TO_HASH(idx)
$81 = 24
(gdb) p idx
$82 = 1
(gdb) p HT_HASH(ht, nIndex)
$83 = 24
(gdb) macro expand HT_HASH(ht, nIndex)
expands to: ((uint32_t*)((ht)->arData))[(int32_t)(nIndex)]
(gdb) macro expand HT_IDX_TO_HASH(idx)
expands to: ((idx) * sizeof(Bucket))
(gdb) p sizeof(Bucket)
$84 = 24
(gdb) p nIndex
$85 = 4294967294
(gdb) p h
$86 = 4238019654
(gdb) p ht->nTableMask
$87 = 4294967288
(gdb) l
610 nIndex = h | ht->nTableMask;
611 Z_NEXT(p->val) = HT_HASH(ht, nIndex);
612 HT_HASH(ht, nIndex) = HT_IDX_TO_HASH(idx);
613 HANDLE_UNBLOCK_INTERRUPTIONS();
614
615 return &p->val;
616 }

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