应用操作-Zend_string 与写时复制

乐宝宝 2021-04-01 AM 978℃ 0条

####新建一个string.php
```html
<?php
//const string 
$c = "hello world!";
echo $c;

$a = time()."string";
echo $a;

//copy on write
$b = $a;
echo $a;
echo $b;
$b = "hello";
echo $a;
echo $b;
```
####执行程序
```html
[jack@192 test]$ gdb /home/jack/Desktop/php-7.1.0/output/bin/php
GNU gdb (GDB) Red Hat Enterprise Linux 7.6.1-80.el7
Copyright (C) 2013 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-redhat-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /home/jack/Desktop/php-7.1.0/output/bin/php...done.
```
####执行端点并运行
```html
(gdb) b ZEND_ECHO_SPEC_CV_HANDLER
Breakpoint 1 at 0x8f607e: file /home/jack/Desktop/php-7.1.0/Zend/zend_vm_execute.h, line 34640.
(gdb) r string.php
Starting program: /home/jack/Desktop/php-7.1.0/output/bin/php string.php
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".

Breakpoint 1, ZEND_ECHO_SPEC_CV_HANDLER () at /home/jack/Desktop/php-7.1.0/Zend/zend_vm_execute.h:34640
34640		SAVE_OPLINE();
Missing separate debuginfos, use: debuginfo-install glibc-2.17-105.el7.x86_64 libxml2-2.9.1-6.el7.4.x86_64 nss-softokn-freebl-3.16.2.3-13.el7_1.x86_64 xz-libs-5.2.2-1.el7.x86_64 zlib-1.2.7-18.el7.x86_64
```
####继续执行下一步
```html
(gdb) n
34641		z = _get_zval_ptr_cv_undef(execute_data, opline->op1.var);
(gdb) n
34643		if (Z_TYPE_P(z) == IS_STRING) {
(gdb) p z
$1 = (zval *) 0x7ffff5e14080
```
####执行的程序是$c，这个是string,常量字符串  (u1 = {v = {type = 6 '\006',)，而且是常量refcount是零，flags是2，type是6
```html
(gdb) p *z
$2 = {value = {lval = 140737318974880, dval = 6.9533474393289609e-310, counted = 0x7ffff5e775a0, 
    str = 0x7ffff5e775a0, arr = 0x7ffff5e775a0, obj = 0x7ffff5e775a0, res = 0x7ffff5e775a0, ref = 0x7ffff5e775a0, 
    ast = 0x7ffff5e775a0, zv = 0x7ffff5e775a0, ptr = 0x7ffff5e775a0, ce = 0x7ffff5e775a0, func = 0x7ffff5e775a0, 
    ww = {w1 = 4125586848, w2 = 32767}}, u1 = {v = {type = 6 '\006', type_flags = 0 '\000', const_flags = 0 '\000', 
      reserved = 0 '\000'}, type_info = 6}, u2 = {next = 0, cache_slot = 0, lineno = 0, num_args = 0, fe_pos = 0, 
    fe_iter_idx = 0, access_flags = 0, property_guard = 0}}
```
####打印出相关字符串的值,hello world!  
```html
(gdb) p $2.value.str
$3 = (zend_string *) 0x7ffff5e775a0
(gdb) p *$2.value.str
$4 = {gc = {refcount = 0, u = {v = {type = 6 '\006', flags = 2 '\002', gc_info = 0}, type_info = 518}}, 
  h = 15212097803322581250, len = 12, val = "h"}
(gdb) p *$2.value.str.val@12
$5 = "hello world!"
```
####继续执行下一步
```html
(gdb) c
Continuing.
hello world!
Breakpoint 1, ZEND_ECHO_SPEC_CV_HANDLER () at /home/jack/Desktop/php-7.1.0/Zend/zend_vm_execute.h:34640
34640		SAVE_OPLINE();
(gdb) n
34641		z = _get_zval_ptr_cv_undef(execute_data, opline->op1.var);
(gdb) n
34643		if (Z_TYPE_P(z) == IS_STRING) {
(gdb) p z
$6 = (zval *) 0x7ffff5e14090
```
####执行的程序是$a = time()."string";这个是变量字符串，refcount是1，type是6，flags是0
```html
(gdb) p *z
$7 = {value = {lval = 140737318975040, dval = 6.953347439336866e-310, counted = 0x7ffff5e77640, 
    str = 0x7ffff5e77640, arr = 0x7ffff5e77640, obj = 0x7ffff5e77640, res = 0x7ffff5e77640, ref = 0x7ffff5e77640, 
    ast = 0x7ffff5e77640, zv = 0x7ffff5e77640, ptr = 0x7ffff5e77640, ce = 0x7ffff5e77640, func = 0x7ffff5e77640, 
    ww = {w1 = 4125587008, w2 = 32767}}, u1 = {v = {type = 6 '\006', type_flags = 20 '\024', const_flags = 0 '\000', 
      reserved = 0 '\000'}, type_info = 5126}, u2 = {next = 0, cache_slot = 0, lineno = 0, num_args = 0, fe_pos = 0, 
    fe_iter_idx = 0, access_flags = 0, property_guard = 0}}
(gdb) p *z.value.str
$8 = {gc = {refcount = 1, u = {v = {type = 6 '\006', flags = 0 '\000', gc_info = 0}, type_info = 6}}, h = 0, 
  len = 16, val = "1"}
(gdb) p *z.value.str.val@16
$9 = "1604996435string"
```
####继续执行
```html
(gdb) c
Continuing.
1604996435string
Breakpoint 1, ZEND_ECHO_SPEC_CV_HANDLER () at /home/jack/Desktop/php-7.1.0/Zend/zend_vm_execute.h:34640
34640		SAVE_OPLINE();
(gdb) n
34641		z = _get_zval_ptr_cv_undef(execute_data, opline->op1.var);
(gdb) n
34643		if (Z_TYPE_P(z) == IS_STRING) {
(gdb) p z
$10 = (zval *) 0x7ffff5e14090
```
####执行的是$b = $a; 0x7ffff5e14090 这个值是跟上面一样的，代表的是没变过 refcount变成了2
```html
(gdb) p *z
$11 = {value = {lval = 140737318975040, dval = 6.953347439336866e-310, counted = 0x7ffff5e77640, 
    str = 0x7ffff5e77640, arr = 0x7ffff5e77640, obj = 0x7ffff5e77640, res = 0x7ffff5e77640, ref = 0x7ffff5e77640, 
    ast = 0x7ffff5e77640, zv = 0x7ffff5e77640, ptr = 0x7ffff5e77640, ce = 0x7ffff5e77640, func = 0x7ffff5e77640, 
    ww = {w1 = 4125587008, w2 = 32767}}, u1 = {v = {type = 6 '\006', type_flags = 20 '\024', const_flags = 0 '\000', 
      reserved = 0 '\000'}, type_info = 5126}, u2 = {next = 0, cache_slot = 0, lineno = 0, num_args = 0, fe_pos = 0, 
    fe_iter_idx = 0, access_flags = 0, property_guard = 0}}
(gdb) p *z.value.str
$12 = {gc = {refcount = 2, u = {v = {type = 6 '\006', flags = 0 '\000', gc_info = 0}, type_info = 6}}, h = 0, 
  len = 16, val = "1"}
```
####继续执行
```html
(gdb) c
Continuing.
1604996435string
Breakpoint 1, ZEND_ECHO_SPEC_CV_HANDLER () at /home/jack/Desktop/php-7.1.0/Zend/zend_vm_execute.h:34640
34640		SAVE_OPLINE();
(gdb) n
34641		z = _get_zval_ptr_cv_undef(execute_data, opline->op1.var);
(gdb) n
34643		if (Z_TYPE_P(z) == IS_STRING) {
(gdb) p z
$13 = (zval *) 0x7ffff5e140a0
```
####执行的是echo $a;很明显$a的值没有变了，指向同一个str 0x7ffff5e77640,
```html
(gdb) p *z
$14 = {value = {lval = 140737318975040, dval = 6.953347439336866e-310, counted = 0x7ffff5e77640, 
    str = 0x7ffff5e77640, arr = 0x7ffff5e77640, obj = 0x7ffff5e77640, res = 0x7ffff5e77640, ref = 0x7ffff5e77640, 
    ast = 0x7ffff5e77640, zv = 0x7ffff5e77640, ptr = 0x7ffff5e77640, ce = 0x7ffff5e77640, func = 0x7ffff5e77640, 
    ww = {w1 = 4125587008, w2 = 32767}}, u1 = {v = {type = 6 '\006', type_flags = 20 '\024', const_flags = 0 '\000', 
      reserved = 0 '\000'}, type_info = 5126}, u2 = {next = 0, cache_slot = 0, lineno = 0, num_args = 0, fe_pos = 0, 
    fe_iter_idx = 0, access_flags = 0, property_guard = 0}}
```
####继续执行
```html
(gdb) c
Continuing.
1604996435string
Breakpoint 1, ZEND_ECHO_SPEC_CV_HANDLER () at /home/jack/Desktop/php-7.1.0/Zend/zend_vm_execute.h:34640
34640		SAVE_OPLINE();
(gdb) n
34641		z = _get_zval_ptr_cv_undef(execute_data, opline->op1.var);
(gdb) n
34643		if (Z_TYPE_P(z) == IS_STRING) {
(gdb) p z
$15 = (zval *) 0x7ffff5e14090
```
####执行的是echo $b;0x7ffff5e14090 还是指向a的内容 0x7ffff5e77640地址没有变  refcount减了1 ，a和b分开了
```html
(gdb) p *z
$16 = {value = {lval = 140737318975040, dval = 6.953347439336866e-310, counted = 0x7ffff5e77640, 
    str = 0x7ffff5e77640, arr = 0x7ffff5e77640, obj = 0x7ffff5e77640, res = 0x7ffff5e77640, ref = 0x7ffff5e77640, 
    ast = 0x7ffff5e77640, zv = 0x7ffff5e77640, ptr = 0x7ffff5e77640, ce = 0x7ffff5e77640, func = 0x7ffff5e77640, 
    ww = {w1 = 4125587008, w2 = 32767}}, u1 = {v = {type = 6 '\006', type_flags = 20 '\024', const_flags = 0 '\000', 
      reserved = 0 '\000'}, type_info = 5126}, u2 = {next = 0, cache_slot = 0, lineno = 0, num_args = 0, fe_pos = 0, 
    fe_iter_idx = 0, access_flags = 0, property_guard = 0}}
(gdb) p *z.value.str
$17 = {gc = {refcount = 1, u = {v = {type = 6 '\006', flags = 0 '\000', gc_info = 0}, type_info = 6}}, h = 0, 
  len = 16, val = "1"}
```
####继续执行
```html
(gdb) c
Continuing.
1604996435string
Breakpoint 1, ZEND_ECHO_SPEC_CV_HANDLER () at /home/jack/Desktop/php-7.1.0/Zend/zend_vm_execute.h:34640
34640		SAVE_OPLINE();
(gdb) n
34641		z = _get_zval_ptr_cv_undef(execute_data, opline->op1.var);
(gdb) n
34643		if (Z_TYPE_P(z) == IS_STRING) {
(gdb) p z
$18 = (zval *) 0x7ffff5e140a0
```
####执行的是$b = "hello";这里很明显$b的值已经发生了变化，0x7ffff5e63d40 很明显地址跟原来不一样了，之前的是0x7ffff5e77640  refcount变成了0  flags是2表示常量字符串
```html
(gdb) p *z
$19 = {value = {lval = 140737318894912, dval = 6.9533474353780168e-310, counted = 0x7ffff5e63d40, 
    str = 0x7ffff5e63d40, arr = 0x7ffff5e63d40, obj = 0x7ffff5e63d40, res = 0x7ffff5e63d40, ref = 0x7ffff5e63d40, 
    ast = 0x7ffff5e63d40, zv = 0x7ffff5e63d40, ptr = 0x7ffff5e63d40, ce = 0x7ffff5e63d40, func = 0x7ffff5e63d40, 
    ww = {w1 = 4125506880, w2 = 32767}}, u1 = {v = {type = 6 '\006', type_flags = 0 '\000', const_flags = 0 '\000', 
      reserved = 0 '\000'}, type_info = 6}, u2 = {next = 0, cache_slot = 0, lineno = 0, num_args = 0, fe_pos = 0, 
    fe_iter_idx = 0, access_flags = 0, property_guard = 0}}
(gdb) p *z.value.str
$20 = {gc = {refcount = 0, u = {v = {type = 6 '\006', flags = 2 '\002', gc_info = 0}, type_info = 518}}, 
  h = 9223372247569412249, len = 5, val = "h"}
(gdb) p *z.value.str.val@5
$21 = "hello"
```

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