gdb方式遍历EG(symbol_table) 哈希表的key

Sara Golemon写过一篇文章，里面提到：“是否存在特别的地方可以找到GLOBALS数组？”答案是“存在”，就是EG(symbol_table)－Executor Globals结构，她也给出了找的具体实例，如下

PHP_FUNCTION(confirm_getGlobal_compiled) {

    char *varname;

    int varname_len;

    zval **varvalue;

    if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "s", &varname, &varname_len) == FAILURE) {

        RETURN_NULL();

    }

    if (zend_hash_find(&EG(symbol_table), varname, varname_len + 1, (void**)&varvalue) == FAILURE) {

        php_error_docref(NULL TSRMLS_CC, E_NOTICE, "Undefined variable: %s", varname);

        RETURN_NULL();

    }

    *return_value = **varvalue;

    zval_copy_ctor(return_value);

}

编译成so加载后，编写php测试代码

$abc = 'string';

$def = 'string2';

var_dump(confirm_getGlobal_compiled('abc'));

执行结果

string(6) "string"

大家可能感觉奇怪，为什么多写了一个def变量，这就是下面要进行的，一起来看下EG这个hashtable

gdb --args bin/php -c php.ini a.php

调试代码如下

(gdb) b renzhi.c : 301     //在写的扩展地方加上断点

No source file named renzhi.c.

Make breakpoint pending on future shared library load? (y or [n]) y

Breakpoint 1 (renzhi.c : 301) pending.

(gdb) r   //运行到断点处

Starting program: /root/php-src-5.3/bin/php -c php.ini ceshi.php

warning: .dynamic section for "/lib/libc.so.6" is not at the expected address

warning: difference appears to be caused by prelink, adjusting expectations

[Thread debugging using libthread_db enabled]

Breakpoint 1, zif_confirm_getGlobal_compiled (ht=1, return_value=0x837a43c, return_value_ptr=0x0, this_ptr=0x0, return_value_used=1)

    at /root/php-src-5.3/ext/renzhi/renzhi.c:305

305         if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "s", &varname, &varname_len) == FAILURE) {

(gdb) n

309         if (zend_hash_find(&EG(symbol_table), varname, varname_len + 1, (void**)&varvalue) == FAILURE) {

(gdb) step    //进入zend_hash_find哈希查找函数

zend_hash_find (ht=0x82e3250, arKey=0x837a42c "abc", nKeyLength=4, pData=0xbfffc484) at /root/php-src-5.3/Zend/zend_hash.c:872

下面看下关键

(gdb) p *ht

$9 = {nTableSize = 64, nTableMask = 63, nNumOfElements = 10, nNextFreeElement = 0, pInternalPointer = 0x83edc98, pListHead = 0x83edc98,

  pListTail = 0x837a3fc, arBuckets = 0x83705a8, pDestructor = 0x81923b0 <_zval_ptr_dtor>, persistent = 0 '/000', nApplyCount = 0 '/000',

  bApplyProtection = 1 '/001'}

(gdb) p *ht.pListHead

$2 = {h = 2572561225, nKeyLength = 8, pData = 0x83edca4, pDataPtr = 0x83edc7c, pListNext = 0x8378c4c, pListLast = 0x0, pNext = 0x0, pLast = 0x0,

  arKey = "G"}

(gdb) p *ht.pListHead.pListNext

$3 = {h = 253399445, nKeyLength = 5, pData = 0x8378c58, pDataPtr = 0x8378b60, pListNext = 0x8378c7c, pListLast = 0x83edc98, pNext = 0x0, pLast = 0x0,

  arKey = "a"}

(gdb) p *ht.pListHead.pListNext.pListNext

$4 = {h = 253398818, nKeyLength = 5, pData = 0x8378c88, pDataPtr = 0x8378c30, pListNext = 0x8378d20, pListLast = 0x8378c4c, pNext = 0x0, pLast = 0x0,

  arKey = "a"}

(gdb) p *ht.pListHead.pListNext.pListNext.pListNext

$5 = {h = 3947724458, nKeyLength = 6, pData = 0x8378d2c, pDataPtr = 0x8378cac, pListNext = 0x8378d54, pListLast = 0x8378c7c, pNext = 0x0, pLast = 0x0,

  arKey = "_"}

(gdb) p *ht.pListHead.pListNext.pListNext.pListNext.pListNext

$6 = {h = 249444164, nKeyLength = 5, pData = 0x8378d60, pDataPtr = 0x83edd1c, pListNext = 0x8378d84, pListLast = 0x8378d20, pNext = 0x0, pLast = 0x0,

  arKey = "_"}

(gdb) p *ht.pListHead.pListNext.pListNext.pListNext.pListNext.pListNext

$7 = {h = 195471710, nKeyLength = 8, pData = 0x8378d90, pDataPtr = 0x83edd38, pListNext = 0x8378e2c, pListLast = 0x8378d54, pNext = 0x0, pLast = 0x0,

  arKey = "_"}

(gdb) p *ht.pListHead.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext

$8 = {h = 1027153623, nKeyLength = 7, pData = 0x8378e38, pDataPtr = 0x8378db8, pListNext = 0x8379e8c, pListLast = 0x8378d84, pNext = 0x0, pLast = 0x0,

  arKey = "_"}

(gdb) p *ht.pListHead.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext

$9 = {h = 3291685243, nKeyLength = 8, pData = 0x8379e98, pDataPtr = 0x8378e88, pListNext = 0x837a3cc, pListLast = 0x8378e2c, pNext = 0x0, pLast = 0x0,

  arKey = "_"}

(gdb) p *ht.pListHead.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext

$10 = {h = 2090069483, nKeyLength = 4, pData = 0x837a3d8, pDataPtr = 0x8379ef8, pListNext = 0x837a3fc, pListLast = 0x8379e8c, pNext = 0x0, pLast = 0x0,

  arKey = "a"}

(gdb) p *ht.pListHead.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext

$11 = {h = 2090180660, nKeyLength = 4, pData = 0x837a408, pDataPtr = 0x8379edc, pListNext = 0x0, pListLast = 0x837a3cc, pNext = 0x0, pLast = 0x0,

  arKey = "d"}

有点乱，这里第一条就是现实了EG这个hash表里面有nNumOfElements =10个元素

这里的

(gdb) p *ht.pListHead.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext

$10 = {h = 2090069483, nKeyLength = 4, pData = 0x837a3d8, pDataPtr = 0x8379ef8, pListNext = 0x837a3fc, pListLast = 0x8379e8c, pNext = 0x0, pLast = 0x0,

  arKey = "a"}

(gdb) p *ht.pListHead.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext

$11 = {h = 2090180660, nKeyLength = 4, pData = 0x837a408, pDataPtr = 0x8379edc, pListNext = 0x0, pListLast = 0x837a3cc, pNext = 0x0, pLast = 0x0,

  arKey = "d"}

就是测试php代码里面的

$abc = 'string';

$def = 'string2';

这两个变量名称的具体hash的bucket了

(gdb) p *ht.pListHead.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext

$10 = {h = 2090069483, nKeyLength = 4, pData = 0x837a3d8, pDataPtr = 0x8379ef8, pListNext = 0x837a3fc, pListLast = 0x8379e8c, pNext = 0x0, pLast = 0x0,

  arKey = "a"}

第一个字符arKey为a，有nKeyLength = 4四个字符长度

(gdb) p ht.pListHead.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext.arKey[0]

$10 = 97 'a'

(gdb) p ht.pListHead.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext.arKey[1]

$11 = 98 'b'

(gdb) p ht.pListHead.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext.arKey[2]

$12 = 99 'c'

(gdb) p ht.pListHead.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext.arKey[3]

$13 = 0 '/000'

如何在gdb方式下拿到指针了，看到对应的执行的zval的内容呢？

已经知道了bucket结构体中的pData就执行了内容

(gdb) p ht.pListHead.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext.pData

$19 = (void *) 0x837a3d8

但是返回的这个，还不知道如何获得，请高手帮助

搞明白了

(gdb) p *ht.pListHead.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext.pListNext

$29 = {h = 2090069483, nKeyLength = 4, pData = 0x839fe28, pDataPtr = 0x839f948, pListNext = 0x839fe4c, pListLast = 0x839f8dc, pNext = 0x0, pLast = 0x0,

  arKey = "a"}

(gdb) p *(zval *)$29->pDataPtr

$30 = {value = {lval = 138024112, dval = 1.2800167717828578e-313, str = {val = 0x83a14b0 "string", len = 6}, ht = 0x83a14b0, obj = {handle = 138024112,

      handlers = 0x6}}, refcount__gc = 1, type = 6 '/006', is_ref__gc = 0 '/000'}

哈哈，可以看到具体的hash指向的值了

但是又有点不明白了pData和pDataPtr到底有啥关系？

(gdb) p &$29->pDataPtr

$46 = (void **) 0x839fe28

(gdb) p $29->pData

$47 = (void *) 0x839fe28

也就是pData里面存得是pDataPtr的地址

摘自 xiaoq3406的专栏