How to generate the function stack trace of the last request made?

Question

Is there a module that can essentially show you the function stack trace of the last request made?

Say I have a form that I submit. After the page loads with the result from the request, I would like to see a list of all the functions that were called, start to finish, that resulted in the currently loaded page.

Answer 1

A function trace will only show you the function calls that lead directly to that piece of code.

PHP provides the functions debug_print_backtrace() for that, which is however not very readable but it will result a huge amount of text. devel.module provides a ddebug_backtrace()function, which us much easier to read.

To see all function calls of a single page, you need to install a profiler like XhProf.

Answer 2

XDebug

You can use PHP XDebug extension with the following options:

• start/stop by xdebug_start_trace()/xdebug_stop_trace() at the specific places (e.g. before form submit),
• set xdebug.auto_trace=1 in php.ini for full trace,
• use xdebug_print_function_stack() to display your current function stack,
• use xdebug.remote_enable=1 in php.ini to use debugger directly from IDE for step-by-step debugging.

Check: XDebug Docs.

See my suggested xdebug.ini config file for PHP.

DTrace

If your system supports DTrace (e.g. OS X) and your PHP has been configured with DTrace static probes (php -i | grep dtrace), the following command will trace all your function calls:

sudo dtrace -qn 'php*:::function-entry { printf("%Y: PHP function-entry:\t%s%s%s() in %s:%d\n", walltimestamp, copyinstr(arg3), copyinstr(arg4), copyinstr(arg0), basename(copyinstr(arg1)), (int)arg2); }'

This should work in Apache, if not, you may re-run your CMS by using builtin PHP server, e.g.:

php -S localhost:8080

then access your site at http://localhost:8080/, so when you submit the form - you should see trace output containing all functions that were called as result of loaded page.

For more scripts, check my dtruss-lamp repository.