Use GDB to debug PHP code to solve the endless PHP code loop Problem

This article mainly introduces how to use GDB to debug PHP code to solve the endless loop of PHP Code. For more information, see

This article mainly introduces how to use GDB to debug PHP code to solve the endless loop of PHP Code. For more information, see

When I recently helped my colleagues solve the Swoole Server problem, I found that one worker process has been in the R state, and the CPU consumption is very high. It was preliminarily determined that it was a life-and-death loop in PHP code.

The following code shows how to solve the PHP endless loop problem.

The Code is as follows:

# Dead_loop.php
$ Array = array ();
For ($ I = 0; I I <10000; $ I ++)
{
$ Array [] = $ I;
}
Include _ DIR _. "/include. php ";
# Include. php
While (1)
{
Usleep (10 );
$ Keys = array_flip ($ array );
$ Index = array_search (rand (1500,999 9), $ array );
$ Str = str_repeat ('A', $ index );
$ Strb = test ($ index, $ str );
}
Function test ($ index, $ str)
{
Return str_replace ('A', 'B', $ str );
}

Obtain the process ID and status through ps aux, use gdb-p process ptrace to trace, and use the bt command to obtain the call stack.

The Code is as follows:

Htf 3834 2.6 0.2 166676 pts/12 R + php dead_loop.php
Gdb-p 3834
(Gdb) bt
#0 0x000000000000008cc03f in seconds (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 0x000000000000008cd643 in _ partition (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/empty", _ zend_orig_lineno = 437) at/home/htf/workspace/php-5.4.27/Zend/zend_alloc.c: 2064
#2 0x000000000000008cebf7 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/empty", _ zend_orig_lineno = 437) at/home/htf/workspace/php-5.4.27/Zend/zend_alloc.c: 2436
#3 Records in _ records (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 0x000000000000008fe687 in _ zval_ptr_dtor_wrapper (zval_ptr = 0x25849a0) at/home/htf/workspace/php-5.4.27/Zend/zend_variables.c: 182
#5 0x0000000000000091259f in zend_hash_destroy (ht = 0x7f00003f6e380) at/home/htf/workspace/php-5.4.27/Zend/zend_hash.c: 560
#6 records in _ records (zvalue = 0x7f00000000fe50, _ 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 = 0x7f00000000fe50, _ 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 = 0x7f00003f8e738, value = 0x7f000000000000f6a8) at/home/htf/workspace/php-5.4.27/Zend/zend_execute.c
#9 0x0000000000997ee5 in ZEND_ASSIGN_SPEC_CV_VAR_HANDLER (execute_data = 0x7f1_d04b2a8) at/home/htf/workspace/php-5.4.27/Zend/zend_vm_execute.h: 33168
#10 0x0000000000000093b5fd 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. c: 2502
#13 0x000000000000009a32e3 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

After gdb is executed, the process of the endless loop changes to the T state, indicating that the Trace is in progress. This is exclusive, so you cannot use strace/gdb or other ptrace tools to debug this process. In addition, this process will interrupt execution. After gdb inputs c, the program continues to run down. Then press ctrl + c again to interrupt the program. Use the bt command to view the call stack of a process.

The Code is as follows:

(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", _ labels = 412) at/home/htf/workspace/php-5.4.27/Zend/zend_alloc.c: 1895
#1 0x000000000000008ceb86 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", _ labels = 412) at/home/htf/workspace/php-5.4.27/Zend/zend_alloc.c: 2425
#2 0x00000000000000911d85 in _ records (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 = 0x7f00000000ea68, 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 = 0x7f1_d04b2a8) at/home/htf/workspace/php-5.4.27/Zend/zend_vm_execute.h: 643
#5 0x000000000000009400e6 in ZEND_DO_FCALL_SPEC_CONST_HANDLER (execute_data = 0x7f1_d04b2a8) at/home/htf/workspace/php-5.4.27/Zend/zend_vm_execute.h: 2233
#6 0x0000000000000093b5fd in execute (op_array = 0x21d58b0) at/home/htf/workspace/php-5.4.27/Zend/zend_vm_execute.h: 410

The two BT messages are different because the program is interrupted at different locations. The line execute (oparray = 0x21d58b0) is displayed. Here is the entry for PHP to execute oparray. Input f 6 under gdb (available by calling the stack number ).

The Code is as follows: