使用GDB調試PHP代碼，解決PHP代碼死循環問題

2020-03-22 20:03:21

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最近在幫同事解決Swoole Server問題時，發現有1個worker進程一直處于R的狀態，而且CPU耗時非常高。初步斷定是PHP代碼中發生死循環。下面通過一段代碼展示如何解決PHP死循環問題。復制代碼代碼如下:
#dead_loop.php
$array = array();
for($i = 0; $i 10000; $i++)
{
$array[] = $i;
}
include __DIR__."/include.php";
#include.php
while(1)
{
usleep(10);
$keys = array_flip($array);
$index = array_search(rand(1500, 9999), $array);
$str = str_repeat('A', $index);
$strb = test($index, $str);
}
function test($index, $str)
{
return str_replace('A', 'B', $str);
}
通過ps aux得到進程ID和狀態如下，使用gdb -p 進程ptrace跟蹤，通過bt命令得到調用棧復制代碼代碼如下:
htf 3834 2.6 0.2 166676 22060 pts/12 R+ 10:50 0:12 php dead_loop.php
gdb -p 3834
(gdb) bt
#0 0x00000000008cc03f in zend_mm_check_ptr (heap=0x1eaa2c0, ptr=0x2584910, silent=1, __zend_filename=0xee3d40 "/home/htf/workspace/php-5.4.27/Zend/zend_variables.c",
__zend_lineno=182, __zend_orig_filename=0xee1888 "/home/htf/workspace/php-5.4.27/Zend/zend_execute_API.c", __zend_orig_lineno=437)
at /home/htf/workspace/php-5.4.27/Zend/zend_alloc.c:1485
#1 0x00000000008cd643 in _zend_mm_free_int (heap=0x1eaa2c0, p=0x2584910, __zend_filename=0xee3d40 "/home/htf/workspace/php-5.4.27/Zend/zend_variables.c", __zend_lineno=182,
__zend_orig_filename=0xee1888 "/home/htf/workspace/php-5.4.27/Zend/zend_execute_API.c", __zend_orig_lineno=437) at /home/htf/workspace/php-5.4.27/Zend/zend_alloc.c:2064
#2 0x00000000008cebf7 in _efree (ptr=0x2584910, __zend_filename=0xee3d40 "/home/htf/workspace/php-5.4.27/Zend/zend_variables.c", __zend_lineno=182,
__zend_orig_filename=0xee1888 "/home/htf/workspace/php-5.4.27/Zend/zend_execute_API.c", __zend_orig_lineno=437) at /home/htf/workspace/php-5.4.27/Zend/zend_alloc.c:2436
#3 0x00000000008eda0a in _zval_ptr_dtor (zval_ptr=0x25849a0, __zend_filename=0xee3d40 "/home/htf/workspace/php-5.4.27/Zend/zend_variables.c", __zend_lineno=182)
at /home/htf/workspace/php-5.4.27/Zend/zend_execute_API.c:437
#4 0x00000000008fe687 in _zval_ptr_dtor_wrapper (zval_ptr=0x25849a0) at /home/htf/workspace/php-5.4.27/Zend/zend_variables.c:182
#5 0x000000000091259f in zend_hash_destroy (ht=0x7f7263f6e380) at /home/htf/workspace/php-5.4.27/Zend/zend_hash.c:560
#6 0x00000000008fe2c5 in _zval_dtor_func (zhtml' target='_blank'>value=0x7f726426fe50, __zend_filename=0xeea290 "/home/htf/workspace/php-5.4.27/Zend/zend_execute.c", __zend_lineno=901)
at /home/htf/workspace/php-5.4.27/Zend/zend_variables.c:45
#7 0x0000000000936656 in _zval_dtor (zvalue=0x7f726426fe50, __zend_filename=0xeea290 "/home/htf/workspace/php-5.4.27/Zend/zend_execute.c", __zend_lineno=901)
at /home/htf/workspace/php-5.4.27/Zend/zend_variables.h:35
#8 0x0000000000939747 in zend_assign_to_variable (variable_ptr_ptr=0x7f7263f8e738, value=0x7f726426f6a8) at /home/htf/workspace/php-5.4.27/Zend/zend_execute.c:901
#9 0x0000000000997ee5 in ZEND_ASSIGN_SPEC_CV_VAR_HANDLER (execute_data=0x7f726d04b2a8) at /home/htf/workspace/php-5.4.27/Zend/zend_vm_execute.h:33168
#10 0x000000000093b5fd in execute (op_array=0x21d58b0) at /home/htf/workspace/php-5.4.27/Zend/zend_vm_execute.h:410
#11 0x0000000000901692 in zend_execute_scripts (type=8, retval=0x0, file_count=3) at /home/htf/workspace/php-5.4.27/Zend/zend.c:1315
#12 0x000000000087926a in php_execute_script (primary_file=0x7ffffe0038d0) at /home/htf/workspace/php-5.4.27/main/main.c:2502
#13 0x00000000009a32e3 in do_cli (argc=2, argv=0x7ffffe004d18) at /home/htf/workspace/php-5.4.27/sapi/cli/php_cli.c:989
#14 0x00000000009a4491 in main (argc=2, argv=0x7ffffe004d18) at /home/htf/workspace/php-5.4.27/sapi/cli/php_cli.c:1365
執行gdb后，死循環的進程會變成T的狀態，表示正在Trace。這個是獨占的，所以不能再使用strace/gdb或者其他ptrace工具對此進程進行調試。另外此進程會中斷執行。gdb輸入c后，程序繼續向下運行。然后再次按下ctrl + c中斷程序。通過bt命令查看進程的調用棧。復制代碼代碼如下:
(gdb) bt
#0 _zend_mm_alloc_int (heap=0x1eaa2c0, size=72, __zend_filename=0xe43410 "/home/htf/workspace/php-5.4.27/ext/standard/array.c", __zend_lineno=2719,
__zend_orig_filename=0xee5a38 "/home/htf/workspace/php-5.4.27/Zend/zend_hash.c", __zend_orig_lineno=412) at /home/htf/workspace/php-5.4.27/Zend/zend_alloc.c:1895
#1 0x00000000008ceb86 in _emalloc (size=72, __zend_filename=0xe43410 "/home/htf/workspace/php-5.4.27/ext/standard/array.c", __zend_lineno=2719,
__zend_orig_filename=0xee5a38 "/home/htf/workspace/php-5.4.27/Zend/zend_hash.c", __zend_orig_lineno=412) at /home/htf/workspace/php-5.4.27/Zend/zend_alloc.c:2425
#2 0x0000000000911d85 in _zend_hash_index_update_or_next_insert (ht=0x2257a10, h=3972, pData=0x7ffffe0012b0, nDataSize=8, pDest=0x0, flag=1,
__zend_filename=0xe43410 "/home/htf/workspace/php-5.4.27/ext/standard/array.c", __zend_lineno=2719) at /home/htf/workspace/php-5.4.27/Zend/zend_hash.c:412
#3 0x00000000007767e1 in zif_array_flip (ht=1, return_value=0x7f726424ea68, return_value_ptr=0x0, this_ptr=0x0, return_value_used=1)
at /home/htf/workspace/php-5.4.27/ext/standard/array.c:2719
#4 0x000000000093c03e in zend_do_fcall_common_helper_SPEC (execute_data=0x7f726d04b2a8) at /home/htf/workspace/php-5.4.27/Zend/zend_vm_execute.h:643
#5 0x00000000009400e6 in ZEND_DO_FCALL_SPEC_CONST_HANDLER (execute_data=0x7f726d04b2a8) at /home/htf/workspace/php-5.4.27/Zend/zend_vm_execute.h:2233
#6 0x000000000093b5fd in execute (op_array=0x21d58b0) at /home/htf/workspace/php-5.4.27/Zend/zend_vm_execute.h:410
兩次的BT信息不一樣，這是因為程序在不同的位置中斷?？吹絜xecute (oparray=0x21d58b0) 這一行，這里就是PHP執行oparray的入口了。gdb下輸入f 6，(通過調用棧編號可得)。復制代碼代碼如下:
(gdb) f 6
#6 0x000000000093b5fd in execute (op_array=0x21d58b0) at /home/htf/workspace/php-5.4.27/Zend/zend_vm_execute.h:410
410 if ((ret = OPLINE- handler(execute_data TSRMLS_CC)) 0) {
(gdb) p *op_array
$2 = {type = 2 '/002', function_name = 0x7f726d086540 "test", scope = 0x0, fn_flags = 134217728, prototype = 0x0, num_args = 2, required_num_args = 2, arg_info = 0x7f726d086bd8,
refcount = 0x7f726d0870f0, opcodes = 0x7f726424d600, last = 8, vars = 0x7f726424e890, last_var = 2, T = 1, brk_cont_array = 0x0, last_brk_cont = 0, try_catch_array = 0x0,
last_try_catch = 0, static_variables = 0x0, this_var = 4294967295, filename = 0x7f726424ba38 "/home/htf/wwwroot/include.php", line_start = 12, line_end = 15, doc_comment = 0x0,
doc_comment_len = 0, early_binding = 4294967295, literals = 0x7f726424eae0, last_literal = 4, run_time_cache = 0x7f726450bfb0, last_cache_slot = 1, reserved = {0x0, 0x0, 0x0, 0x0}}
這里的filename就能看到op_array是哪個PHP文件的。然后輸入f 0進入當前位置。復制代碼代碼如下:
(gdb) p **executor_globals.opline_ptr
$4 = {handler = 0x93ff9c , op1 = {constant = 1680133296, var = 1680133296, num = 1680133296, hash = 140129283132592, opline_num = 1680133296,
jmp_addr = 0x7f726424ccb0, zv = 0x7f726424ccb0, literal = 0x7f726424ccb0, ptr = 0x7f726424ccb0}, op2 = {constant = 0, var = 0, num = 0, hash = 0, opline_num = 0, jmp_addr = 0x0,
zv = 0x0, literal = 0x0, ptr = 0x0}, result = {constant = 32, var = 32, num = 32, hash = 32, opline_num = 32, jmp_addr = 0x20, zv = 0x20, literal = 0x20, ptr = 0x20},
extended_value = 1, lineno = 5, opcode = 60 '
這里的lineno表示OPCODE所在的代碼行數，可以到對應文件里去看下是哪行代碼。使用GDB可以查看到更多的信息，這里就不再一一介紹了，有興趣各位可以自行嘗試。zbacktrace的使用zend官方提供了一個gdb的腳本，對指令進行了封裝，可以直接看到php函數的調用關系。在php源代碼包的根目錄中有一個.gdbinit。使用復制代碼代碼如下:
source your_php_src_path/.gdbinit
zbacktrace
可以直接看到PHP函數的調用堆棧。以上就是本文的全部內容了，希望大家能夠喜歡。PHP教程

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