应用操作-Zend_reference引用类型的使用

乐宝宝 2021-04-01 AM 1055℃ 0条

####首先新建一个PHP
```html
<?php
$a = "string";
$b = &$a;

echo $a;
echo $b;

$b = "hello!";
echo $a;
echo $b;

unset($b);
echo $b;
echo $a;
```
####开干
```html
[jack@192 test]$  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.
(gdb) 
```
####打断点
```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.
```
####执行index.php
```html
(gdb) r index.php
Starting program: /home/jack/Desktop/php-7.1.0/output/bin/php index.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
```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
```
####打印里面的内容，u1 = {v = {type = 10 '\n'，类型变成了10,10对应的是IS_REFERENCE
```html
(gdb) p *z
$2 = {value = {lval = 140737318490336, dval = 6.9533474153893065e-310, 
    counted = 0x7ffff5e010e0, str = 0x7ffff5e010e0, arr = 0x7ffff5e010e0, 
    obj = 0x7ffff5e010e0, res = 0x7ffff5e010e0, ref = 0x7ffff5e010e0, 
    ast = 0x7ffff5e010e0, zv = 0x7ffff5e010e0, ptr = 0x7ffff5e010e0, 
    ce = 0x7ffff5e010e0, func = 0x7ffff5e010e0, ww = {w1 = 4125102304, 
      w2 = 32767}}, u1 = {v = {type = 10 '\n', type_flags = 4 '\004', 
      const_flags = 0 '\000', reserved = 0 '\000'}, type_info = 1034}, u2 = {
    next = 0, cache_slot = 0, lineno = 0, num_args = 0, fe_pos = 0, 
    fe_iter_idx = 0, access_flags = 0, property_guard = 0}}

```
####继续往下走
```html
(gdb) c
Continuing.
string
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) {

# u1 = {v = {type = 10 '\n'，很明显b也是引用类型滴，对应的都是指向同一个地址0x7ffff5e010e0
(gdb) p *z
$3 = {value = {lval = 140737318490336, dval = 6.9533474153893065e-310, 
    counted = 0x7ffff5e010e0, str = 0x7ffff5e010e0, arr = 0x7ffff5e010e0, 
    obj = 0x7ffff5e010e0, res = 0x7ffff5e010e0, ref = 0x7ffff5e010e0, 
    ast = 0x7ffff5e010e0, zv = 0x7ffff5e010e0, ptr = 0x7ffff5e010e0, 
    ce = 0x7ffff5e010e0, func = 0x7ffff5e010e0, ww = {w1 = 4125102304, 
      w2 = 32767}}, u1 = {v = {type = 10 '\n', type_flags = 4 '\004', 
      const_flags = 0 '\000', reserved = 0 '\000'}, type_info = 1034}, u2 = {
    next = 0, cache_slot = 0, lineno = 0, num_args = 0, fe_pos = 0, 
    fe_iter_idx = 0, access_flags = 0, property_guard = 0}}
```
####看看他的值
```html
(gdb) p $3.value.ref
$4 = (zend_reference *) 0x7ffff5e010e0
```
####把内容打印出来
```html
(gdb) p *$3.value.ref
$5 = {gc = {refcount = 2, u = {v = {type = 10 '\n', flags = 0 '\000', 
        gc_info = 0}, type_info = 10}}, val = {value = {lval = 17730720, 
      dval = 8.7601396280303069e-317, counted = 0x10e8ca0, str = 0x10e8ca0, 
      arr = 0x10e8ca0, obj = 0x10e8ca0, res = 0x10e8ca0, ref = 0x10e8ca0, 
      ast = 0x10e8ca0, zv = 0x10e8ca0, ptr = 0x10e8ca0, ce = 0x10e8ca0, 
      func = 0x10e8ca0, ww = {w1 = 17730720, w2 = 0}}, u1 = {v = {
        type = 6 '\006', type_flags = 0 '\000', const_flags = 0 '\000', 
        reserved = 0 '\000'}, type_info = 6}, u2 = {next = 7631717, 
      cache_slot = 7631717, lineno = 7631717, num_args = 7631717, 
      fe_pos = 7631717, fe_iter_idx = 7631717, access_flags = 7631717, 
      property_guard = 7631717}}}
```
####把内容打印出来 
```html
(gdb) p *$3.value.ref.val.value.str
$6 = {gc = {refcount = 1, u = {v = {type = 6 '\006', flags = 7 '\a', gc_info = 0}, type_info = 1798}}, h = 9223378990886268924, len = 6, val = "s"}
```
####把值打印出来，他们都执行同一个zend_reference
```html
(gdb) p *$3.value.ref.val.value.str.val@6
$7 = "string"
```
####继续执行
```html
(gdb) c
Continuing.
string
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
$8 = (zval *) 0x7ffff5e14080
```
####这里b的值已经发生了改变
```html
(gdb) p *z
$9 = {value = {lval = 140737318490336, dval = 6.9533474153893065e-310, 
    counted = 0x7ffff5e010e0, str = 0x7ffff5e010e0, arr = 0x7ffff5e010e0, 
    obj = 0x7ffff5e010e0, res = 0x7ffff5e010e0, ref = 0x7ffff5e010e0, 
    ast = 0x7ffff5e010e0, zv = 0x7ffff5e010e0, ptr = 0x7ffff5e010e0, 
    ce = 0x7ffff5e010e0, func = 0x7ffff5e010e0, ww = {w1 = 4125102304, 
      w2 = 32767}}, u1 = {v = {type = 10 '\n', type_flags = 4 '\004', 
      const_flags = 0 '\000', reserved = 0 '\000'}, type_info = 1034}, 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.ref
$10 = {gc = {refcount = 2, u = {v = {type = 10 '\n', flags = 0 '\000', 
        gc_info = 0}, type_info = 10}}, val = {value = {
      lval = 140737318894656, dval = 6.9533474353653687e-310, 
      counted = 0x7ffff5e63c40, str = 0x7ffff5e63c40, arr = 0x7ffff5e63c40, 
      obj = 0x7ffff5e63c40, res = 0x7ffff5e63c40, ref = 0x7ffff5e63c40, 
      ast = 0x7ffff5e63c40, zv = 0x7ffff5e63c40, ptr = 0x7ffff5e63c40, 
      ce = 0x7ffff5e63c40, func = 0x7ffff5e63c40, ww = {w1 = 4125506624, 
        w2 = 32767}}, u1 = {v = {type = 6 '\006', type_flags = 0 '\000', 
        const_flags = 0 '\000', reserved = 0 '\000'}, type_info = 6}, u2 = {
      next = 7631717, cache_slot = 7631717, lineno = 7631717, 
      num_args = 7631717, fe_pos = 7631717, fe_iter_idx = 7631717, 
      access_flags = 7631717, property_guard = 7631717}}}
(gdb) p *z.value.ref.val.value.str
$11 = {gc = {refcount = 0, u = {v = {type = 6 '\006', flags = 2 '\002', 
        gc_info = 0}, type_info = 518}}, h = 9223378990437778394, len = 6, 
  val = "h"}
(gdb) p *z.value.ref.val.value.str.val@6
$12 = "hello!"
```
####继续执行
```html
(gdb) c
Continuing.
hello!
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 *) 0x7ffff5e14090
(gdb) p *z
$14 = {value = {lval = 140737318490336, dval = 6.9533474153893065e-310, 
    counted = 0x7ffff5e010e0, str = 0x7ffff5e010e0, arr = 0x7ffff5e010e0, 
    obj = 0x7ffff5e010e0, res = 0x7ffff5e010e0, ref = 0x7ffff5e010e0, 
    ast = 0x7ffff5e010e0, zv = 0x7ffff5e010e0, ptr = 0x7ffff5e010e0, 
    ce = 0x7ffff5e010e0, func = 0x7ffff5e010e0, ww = {w1 = 4125102304, 
      w2 = 32767}}, u1 = {v = {type = 10 '\n', type_flags = 4 '\004', 
      const_flags = 0 '\000', reserved = 0 '\000'}, type_info = 1034}, 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.ref
$15 = {gc = {refcount = 2, u = {v = {type = 10 '\n', flags = 0 '\000', 
        gc_info = 0}, type_info = 10}}, val = {value = {
      lval = 140737318894656, dval = 6.9533474353653687e-310, 
      counted = 0x7ffff5e63c40, str = 0x7ffff5e63c40, arr = 0x7ffff5e63c40, 
      obj = 0x7ffff5e63c40, res = 0x7ffff5e63c40, ref = 0x7ffff5e63c40, 
      ast = 0x7ffff5e63c40, zv = 0x7ffff5e63c40, ptr = 0x7ffff5e63c40, 
      ce = 0x7ffff5e63c40, func = 0x7ffff5e63c40, ww = {w1 = 4125506624, 
        w2 = 32767}}, u1 = {v = {type = 6 '\006', type_flags = 0 '\000', 
        const_flags = 0 '\000', reserved = 0 '\000'}, type_info = 6}, u2 = {
      next = 7631717, cache_slot = 7631717, lineno = 7631717, 
      num_args = 7631717, fe_pos = 7631717, fe_iter_idx = 7631717, 
      access_flags = 7631717, property_guard = 7631717}}}
(gdb) p *z.value.ref.val.value.str
$16 = {gc = {refcount = 0, u = {v = {type = 6 '\006', flags = 2 '\002', 
        gc_info = 0}, type_info = 518}}, h = 9223378990437778394, len = 6, 
  val = "h"}
(gdb) p *z.value.ref.val.value.str.val@6
$17 = "hello!"
```
####继续执行
```html
(gdb) c
Continuing.
hello!
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 *) 0x7ffff5e14090

# 执行unset操作，你看类型u1 = {v = {type = 0 '\000'  是0，就是IS_NULL了,ref指针地址都没有发生变化
(gdb) p *z
$19 = {value = {lval = 140737318490336, dval = 6.9533474153893065e-310, 
    counted = 0x7ffff5e010e0, str = 0x7ffff5e010e0, arr = 0x7ffff5e010e0, 
    obj = 0x7ffff5e010e0, res = 0x7ffff5e010e0, ref = 0x7ffff5e010e0, 
    ast = 0x7ffff5e010e0, zv = 0x7ffff5e010e0, ptr = 0x7ffff5e010e0, 
    ce = 0x7ffff5e010e0, func = 0x7ffff5e010e0, ww = {w1 = 4125102304, 
      w2 = 32767}}, u1 = {v = {type = 0 '\000', type_flags = 0 '\000', 
      const_flags = 0 '\000', reserved = 0 '\000'}, type_info = 0}, 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.

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
$20 = (zval *) 0x7ffff5e14080
(gdb) p *z
$21 = {value = {lval = 140737318490336, dval = 6.9533474153893065e-310, 
    counted = 0x7ffff5e010e0, str = 0x7ffff5e010e0, arr = 0x7ffff5e010e0, 
    obj = 0x7ffff5e010e0, res = 0x7ffff5e010e0, ref = 0x7ffff5e010e0, 
    ast = 0x7ffff5e010e0, zv = 0x7ffff5e010e0, ptr = 0x7ffff5e010e0, 
    ce = 0x7ffff5e010e0, func = 0x7ffff5e010e0, ww = {w1 = 4125102304, 
      w2 = 32767}}, u1 = {v = {type = 10 '\n', type_flags = 4 '\004', 
      const_flags = 0 '\000', reserved = 0 '\000'}, type_info = 1034}, 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.ref
$22 = {gc = {refcount = 1, u = {v = {type = 10 '\n', flags = 0 '\000', 
        gc_info = 0}, type_info = 10}}, val = {value = {
      lval = 140737318894656, dval = 6.9533474353653687e-310, 
      counted = 0x7ffff5e63c40, str = 0x7ffff5e63c40, arr = 0x7ffff5e63c40, 
      obj = 0x7ffff5e63c40, res = 0x7ffff5e63c40, ref = 0x7ffff5e63c40, 
      ast = 0x7ffff5e63c40, zv = 0x7ffff5e63c40, ptr = 0x7ffff5e63c40, 
      ce = 0x7ffff5e63c40, func = 0x7ffff5e63c40, ww = {w1 = 4125506624, 
        w2 = 32767}}, u1 = {v = {type = 6 '\006', type_flags = 0 '\000', 
        const_flags = 0 '\000', reserved = 0 '\000'}, type_info = 6}, u2 = {
      next = 7631717, cache_slot = 7631717, lineno = 7631717, 
      num_args = 7631717, fe_pos = 7631717, fe_iter_idx = 7631717, 
      access_flags = 7631717, property_guard = 7631717}}}
# 依然保持原样    
(gdb) p *z.value.ref.val.value.str
$23 = {gc = {refcount = 0, u = {v = {type = 6 '\006', flags = 2 '\002', 
        gc_info = 0}, type_info = 518}}, h = 9223378990437778394, len = 6, 
  val = "h"}
(gdb) p *z.value.ref.val.value.str.val@6
$24 = "hello!"
```

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懂得越多，越发觉懂得越少。2019年12月11日 23:37:41

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