如何使用GDB调试PHP程序

一般来说，GDB主要完成下面四个方面的功能：

(1)启动你的程序，可以按照你的自定义的要求随心所欲的运行程序。
(2)可让被调试的程序在你所指定的调置的断点处停住。（断点可以是条件表达式）
(3)当程序被停住时，可以检查此时你的程序中所发生的事。
(4)动态的改变你程序的执行环境。

1、简介

GDB是GNU开源组织发布的一个强大的UNIX下的程序调试工具。如果你是在 UNIX平台下做软件，你会发现GDB这个调试工具有比VC、BCB的图形化调试器更强大的功能。同时GDB也具有例如ddd这样的图形化的调试端。

2、调试C/C++程序

直接上代码了

#include<iostream>
using namespace std;
long factorial(int n); 
int main()
{
int n(0);
cin>>n;
long val=factorial(n);
cout<<val<<endl;
cin.get();
return 0;
}
long factorial(int n)
{
long result(1);
while(n--)
{ 
result*=n;
} 
return result;
}

编译

1

g++ k.cpp -g -Wall -Werror -o main

开始调试

[root@localhost code]# gdb ./main
GNU gdb (GDB) Red Hat Enterprise Linux (7.2-83.el6)
Copyright (C) 2010 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 "i686-redhat-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /code/main...done.
(gdb) l 

warning: Source file is more recent than executable.
1 #include<iostream>
2 using namespace std;
3 long factorial(int n);
4
5 int main()
6 {
7 int n(0);
8 cin>>n;
9 long val=factorial(n);
10 cout<<val<<endl;
(gdb)

设置断点 break linenumber

(gdb) b 9
Breakpoint 1 at 0x80486f9: file k.cpp, line 9.
(gdb) r
Starting program: /code/main 
4
Breakpoint 1, main () at k.cpp:9
9 long val=factorial(n);

设置观察点 watch var

(gdb) s
factorial (n=4) at k.cpp:17
17 long result(1);
(gdb) l
12 return 0;
13 }
14
15 long factorial(int n)
16 {
17 long result(1);
18 while(n--)
19 {
20 result*=n;
21 }
(gdb) watch n
Hardware watchpoint 2: n
(gdb) watch result
Hardware watchpoint 3: result
(gdb) c
Continuing.
Hardware watchpoint 3: result
Old value = 0
New value = 1
factorial (n=4) at k.cpp:18
18 while(n--)
(gdb) 
Continuing.
Hardware watchpoint 2: n
Old value = 4
New value = 3
0x08048764 in factorial (n=3) at k.cpp:18
18 while(n--)
(gdb) 
Continuing.
Hardware watchpoint 3: result
Old value = 1
New value = 3
factorial (n=3) at k.cpp:18
18 while(n--)
(gdb) 
Continuing.
Hardware watchpoint 2: n
Old value = 3
New value = 2
0x08048764 in factorial (n=2) at k.cpp:18
18 while(n--)
(gdb) 
Continuing.
Hardware watchpoint 3: result
Old value = 3
New value = 6
factorial (n=2) at k.cpp:18
18 while(n--)
(gdb) 
Continuing.
Hardware watchpoint 2: n
Old value = 2
New value = 1
0x08048764 in factorial (n=1) at k.cpp:18
18 while(n--)
(gdb) 
Continuing.
Hardware watchpoint 2: n
Old value = 1
New value = 0
0x08048764 in factorial (n=0) at k.cpp:18
18 while(n--)
(gdb) 
Continuing.
Watchpoint 2 deleted because the program has left the block in
which its expression is valid.
Watchpoint 3 deleted because the program has left the block in
which its expression is valid.
0x08048705 in main () at k.cpp:9
9 long val=factorial(n);
(gdb) p val
$1 = 11476980
(gdb)

可以看到是while那里，导致n越界了，fix

while(n>0) //doesn't let n reach 0
{
result*=n;
n--; //decrements only after the evaluation
}

一些快捷命令

l ? list
p ? print print {variable}
c ? continue
s ? step
b - break break line_number/break [file_name]:line_number/break [file_name]:func_name
r - run
set <var> = <value>
watch <var>

ENTER: pressing enter key would execute the previously executed command again.

c/n/s的区别

•c or continue: Debugger will continue executing until the next break point.
•n or next: Debugger will execute the next line as single instruction.
•s or step: Same as next, but does not treats function as a single instruction, instead goes into the function and executes it line by line

3、调试PHP程序

PHP代码

<?php. 
for($i = 0; $i < 10; $i++){
echo $i."\n";
sleep(3);
if(in_array($i,[1,9,20])){
print_r($i*$i);
var_dump($i*$i); 
print $i*$i;
} 
}

开始调试，加上断点

[root@localhost code]# gdb php 
GNU gdb (GDB) Red Hat Enterprise Linux (7.2-83.el6)
Copyright (C) 2010 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 "i686-redhat-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /usr/bin/php...done.
(gdb) b zif_sleep
Breakpoint 1 at 0x8435180: file /usr/local/src/php-5.5.23/ext/standard/basic_functions.c, line 4449.
(gdb) b zif_in_array
Breakpoint 2 at 0x8426923: file /usr/local/src/php-5.5.23/ext/standard/array.c, line 1215.
(gdb) b zif_print_r
Breakpoint 3 at 0x8438273: file /usr/local/src/php-5.5.23/ext/standard/basic_functions.c, line 5553.
(gdb) b zif_var_dump
Breakpoint 4 at 0x847d296: file /usr/local/src/php-5.5.23/ext/standard/var.c, line 178.
(gdb) b zif_printf
Function "zif_printf" not defined.
Make breakpoint pending on future shared library load? (y or [n]) n
(gdb) b zif_sprintf
Function "zif_sprintf" not defined.
Make breakpoint pending on future shared library load? (y or [n]) n
(gdb) b printf
Breakpoint 5 at 0x806a390
(gdb) b memcpy
Breakpoint 6 at 0x8069390
(gdb) b zif_print
Function "zif_print" not defined.
Make breakpoint pending on future shared library load? (y or [n]) n
(gdb) b zif_echo 
Function "zif_echo" not defined.
Make breakpoint pending on future shared library load? (y or [n]) n
(gdb) info b
Num Type Disp Enb Address What
1 breakpoint keep y 0x08435180 in zif_sleep at /usr/local/src/php-5.5.23/ext/standard/basic_functions.c:4449
2 breakpoint keep y 0x08426923 in zif_in_array at /usr/local/src/php-5.5.23/ext/standard/array.c:1215
3 breakpoint keep y 0x08438273 in zif_print_r at /usr/local/src/php-5.5.23/ext/standard/basic_functions.c:5553
4 breakpoint keep y 0x0847d296 in zif_var_dump at /usr/local/src/php-5.5.23/ext/standard/var.c:178
5 breakpoint keep y 0x0806a390 <printf@plt>
6 breakpoint keep y 0x08069390 <memcpy@plt>
(gdb)

加几个断点测试一下 syntax：break [file_name]:func_name，这里大致可以看一下 echo print等不是函数了

然后开始调试

(gdb) p *return_value
$1 = {value = {lval = 1515870810, dval = 1.7838867517321418e+127, str = {val = 0x5a5a5a5a <Address 0x5a5a5a5a out of bounds>, 
len = 1515870810}, ht = 0x5a5a5a5a, obj = {handle = 1515870810, handlers = 0x5a5a5a5a}}, refcount__gc = 1, type = 0 '\000', is_ref__gc = 0 '\000'}
(gdb) p return_value->value
$2 = {lval = 1515870810, dval = 1.7838867517321418e+127, str = {val = 0x5a5a5a5a <Address 0x5a5a5a5a out of bounds>, 
len = 1515870810}, ht = 0x5a5a5a5a, obj = {handle = 1515870810, handlers = 0x5a5a5a5a}}
(gdb) p return_value->value->lval
$3 = 1515870810

我们还可以使用内置的gdbinit来调试

(gdb) source /usr/local/src/php-5.5.23/.gdbinit
(gdb) zbacktrace
[0xb7fa1144] sleep(3) /code/kk.php:4

查看当前堆栈，PHP内核的执行过程

(gdb) bt
#0 zif_sleep (ht=1, return_value=0xb7fbd6f0, return_value_ptr=0x0, this_ptr=0x0, return_value_used=0)
at /usr/local/src/php-5.5.23/ext/standard/basic_functions.c:4449
#1 0x085f6870 in execute_internal (execute_data_ptr=0xb7fa1144, fci=0x0, return_value_used=0)
at /usr/local/src/php-5.5.23/Zend/zend_execute.c:1484
#2 0x085aea5f in dtrace_execute_internal (execute_data_ptr=0xb7fa1144, fci=0x0, return_value_used=0)
at /usr/local/src/php-5.5.23/Zend/zend_dtrace.c:97
#3 0x00935c33 in pt_execute_core (internal=1, execute_data=0xb7fa1144, fci=0x0, rvu=0)
at /usr/local/src/trace-0.3.0/extension/trace.c:941
#4 0x00935e49 in pt_execute_internal (execute_data=0xb7fa1144, fci=0x0, return_value_used=0)
at /usr/local/src/trace-0.3.0/extension/trace.c:1005
#5 0x085f7523 in zend_do_fcall_common_helper_SPEC (execute_data=0xb7fa1144) at /usr/local/src/php-5.5.23/Zend/zend_vm_execute.h:552
#6 0x085fb2a9 in ZEND_DO_FCALL_SPEC_CONST_HANDLER (execute_data=0xb7fa1144) at /usr/local/src/php-5.5.23/Zend/zend_vm_execute.h:2332
#7 0x085f6deb in execute_ex (execute_data=0xb7fa1144) at /usr/local/src/php-5.5.23/Zend/zend_vm_execute.h:363
#8 0x085ae9dc in dtrace_execute_ex (execute_data=0xb7fa1144) at /usr/local/src/php-5.5.23/Zend/zend_dtrace.c:73
#9 0x00935c5e in pt_execute_core (internal=0, execute_data=0xb7fa1144, fci=0x0, rvu=0)
at /usr/local/src/trace-0.3.0/extension/trace.c:946
#10 0x00935e10 in pt_execute_ex (execute_data=0xb7fa1144) at /usr/local/src/trace-0.3.0/extension/trace.c:1000
#11 0x085f6e4a in zend_execute (op_array=0xb7fbc7b4) at /usr/local/src/php-5.5.23/Zend/zend_vm_execute.h:388
#12 0x085c1cf2 in zend_execute_scripts (type=8, retval=0x0, file_count=3) at /usr/local/src/php-5.5.23/Zend/zend.c:1327
#13 0x085470f9 in php_execute_script (primary_file=0xbffff4a4) at /usr/local/src/php-5.5.23/main/main.c:2525
#14 0x0865af46 in do_cli (argc=2, argv=0x8b9b908) at /usr/local/src/php-5.5.23/sapi/cli/php_cli.c:994
#15 0x0865bff3 in main (argc=2, argv=0x8b9b908) at /usr/local/src/php-5.5.23/sapi/cli/php_cli.c:1378

查看代码段

(gdb) l
4444 Delay for a given number of seconds */
4445 PHP_FUNCTION(sleep)
4446 {
4447 long num;
4448
4449 if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "l", &num) == FAILURE) {
4450 RETURN_FALSE;
4451 }
4452 if (num < 0) {
4453 php_error_docref(NULL TSRMLS_CC, E_WARNING, "Number of seconds must be greater than or equal to 0");
(gdb) l 4450
4445 PHP_FUNCTION(sleep)
4446 {
4447 long num;
4448
4449 if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "l", &num) == FAILURE) {
4450 RETURN_FALSE;
4451 }
4452 if (num < 0) {
4453 php_error_docref(NULL TSRMLS_CC, E_WARNING, "Number of seconds must be greater than or equal to 0");
4454 RETURN_FALSE;
(gdb) l zif_usleep
4463 /* }}} */
4464
4465 /* {{{ proto void usleep(int micro_seconds)
4466 Delay for a given number of micro seconds */
4467 PHP_FUNCTION(usleep)
4468 {
4469 #if HAVE_USLEEP
4470 long num;
4471
4472 if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "l", &num) == FAILURE) {

继续执行

(gdb) n
4452 if (num < 0) {
(gdb) p num
$6 = 3
(gdb) n
4457 RETURN_LONG(php_sleep(num));
(gdb) n
4462 }
(gdb) n
execute_internal (execute_data_ptr=0xb7fa1144, fci=0x0, return_value_used=0) at /usr/local/src/php-5.5.23/Zend/zend_execute.c:1488
1488 }

到了execute_internal ，可以查看一下当前函数的一个状态

(gdb) p execute_data_ptr
$7 = (zend_execute_data *) 0xb7fa1144
(gdb) p *execute_data_ptr
$8 = {opline = 0xb7fbcacc, function_state = {function = 0x8bcf3e8, arguments = 0xb7fa119c}, op_array = 0xb7fbc7b4, object = 0x0, 
symbol_table = 0x8b99cdc, prev_execute_data = 0x0, old_error_reporting = 0x0, nested = 0 '\000', 
original_return_value = 0x38b4ac9, current_scope = 0x49, current_called_scope = 0x45, current_this = 0x0, fast_ret = 0x0, 
call_slots = 0xb7fa1188, call = 0xb7fa1188}
(gdb) p *execute_data_ptr->function_state.function->common->function_name
$9 = 115 's'
(gdb) p execute_data_ptr->function_state.function->common->function_name 
$10 = 0x8af03c9 "sleep"
(gdb) p execute_data_ptr->op_array->filename
$11 = 0xb7fbc8e8 "/code/kk.php"

查看当前hashtable

(gdb) p *execute_data_ptr->symbol_table
$ = {nTableSize = , nTableMask = , nNumOfElements = , nNextFreeElement = , pInternalPointer = xbfbc, 
pListHead = xbfbc, pListTail = xbfbd, arBuckets = xbfb, pDestructor = xbff <_zval_ptr_dtor_wrapper>, 
persistent = '\', nApplyCount = '\', bApplyProtection = '\', inconsistent = }

继续执行输出c之后，回车即可，同样可以看到in_array的执行信息

(gdb) p *execute_data_ptr->function_state.function
$24 = {type = 1 '\001', common = {type = 1 '\001', function_name = 0x8af1841 "in_array", scope = 0x0, fn_flags = 256, 
prototype = 0x0, num_args = 3, required_num_args = 2, arg_info = 0x8ae7554}, op_array = {type = 1 '\001', 
function_name = 0x8af1841 "in_array", scope = 0x0, fn_flags = 256, prototype = 0x0, num_args = 3, required_num_args = 2, 
arg_info = 0x8ae7554, refcount = 0x842691d, opcodes = 0x8bcf120, last = 0, vars = 0x0, last_var = 0, T = 1, 
nested_calls = 3086618796, used_stack = 0, brk_cont_array = 0x0, last_brk_cont = 1, try_catch_array = 0xb7fa10dd, 
last_try_catch = 96, has_finally_block = 160 '\240', static_variables = 0x0, this_var = 11482064, 
filename = 0xaf1ff4 "|\035\257", line_start = 11482016, line_end = 146381272, 
doc_comment = 0xbffff238 "x\362\377\277\244\aY\b\021", doc_comment_len = 10305959, early_binding = 11085989, 
literals = 0x8b7a0a0, last_literal = 140062666, run_time_cache = 0xb7fa10d4, last_cache_slot = 90, reserved = {0x9, 0x8b5f7ac, 
0x796, 0x0}}, internal_function = {type = 1 '\001', function_name = 0x8af1841 "in_array", scope = 0x0, fn_flags = 256, 
prototype = 0x0, num_args = 3, required_num_args = 2, arg_info = 0x8ae7554, handler = 0x842691d <zif_in_array>, 
module = 0x8bcf120}}
(gdb) p execute_data_ptr->function_state.function->common->function_name 
$26 = 0x8af1841 "in_array"
(gdb) p execute_data_ptr->op_array->filename 
$27 = 0xb7fbc8e8 "/code/kk.php"

还可以加一下监控watch、设置一些调试变量set 等等

其他的调试工具还有 strace 查看系统调用、ltrace 查看类库的调用、vld查看opcode。

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