Debugging with gdb and valgrind
%gdb --args php% ~....~
%run%
%bt%
%frame framenr%
%p varname%
%valgrind php% ~....~
To make it easier:
Make sure PHP is compiled in debug mode
Disable the Zend memory manager: %export USE_ZEND_ALLOC=0%
Disable shared extension unloading: %export ZEND_DONT_UNLOAD_MODULES=1%