How to Pinpoint the PHP Code Behind CPU Spikes Using GDB

When a PHP process that normally uses little CPU suddenly spikes to almost 100%, you need to identify the exact code line responsible. The approach is to inspect the Zend executor globals to find the currently executing file, function, and line number.

The key structures are executor_globals.active_op_array and executor_globals.current_execute_data. active_op_array holds the filename and function_name, while current_execute_data contains the currently executing opline whose lineno field gives the line number.

<code>struct _zend_executor_globals { ... zend_op_array *active_op_array; struct _zend_execute_data *current_execute_data; ... }; </code>

<code>struct _zend_op_array { char *filename; char *function_name; zend_op *opcodes; ... }; </code>

<code>struct _zend_execute_data { struct _zend_op *opline; zend_op_array *op_array; ... }; </code>

<code>struct _zend_op { uint lineno; // source line number zend_uchar opcode; // opcode identifier ... }; </code>

Using GDB, attach to the PHP process (e.g., PID 14973) and run:

print (char *)executor_globals.active_op_array->filename
print (char *)executor_globals.active_op_array->function_name
print executor_globals->current_execute_data->opline->lineno

The output shows the script path, function name, and line number currently being executed, allowing you to pinpoint the hot loop (e.g., a sleep(1) call on line 4).

If typing these commands each time is cumbersome, place the following in a .gdbinit file in your home directory (the file is included in the PHP source tree):

source /home/youruser/.gdbinit
zbacktrace

The custom zbacktrace command prints a backtrace with file names and line numbers, e.g.:

[0xa453f34] sleep(1) /home/xinhailong/test/php/test.php:4
[0xa453ed0] test1() /home/xinhailong/test/php/test.php:7

From PHP 5.6 onward, the built‑in phpdbg debugger offers similar capabilities for PHP scripts.