Programming PHP

If you efree( ) something that was allocated using malloc( ) or some mechanism
other than the PHP memory-management functions, you get the following:
--------------------------------------foo.c(124)
: Block 0x08219C94 status:
Beginning: Overrun (magic=0x00000000, expected=0x7312F8DC)
End: Unknown
--------------------------------------foo.c(124)
: Block 0x0821EB1C status:
Beginning: Overrun (magic=0x00000000, expected=0x7312F8DC)
End: Unknown
---------------------------------------
In this case, line 124 in foo.c is the call to efree( ). PHP knows it didn’t allocate this
memory because it didn’t contain the magic token that indicates a PHP allocation.
The emalloc( )/efree( ) safety net also catches overruns—e.g., if you emalloc(20) but
write 21 bytes to that address. For example:
123: s = emalloc(6);
124: strcpy(s,"Rasmus");
125: efree(s);
Because this code failed to allocate enough memory to hold the string and the terminating
NULL, PHP prints this warning:
-------------------------------------foo.c(125)
: Block 0x08219CB8 status:
Beginning: OK (allocated on foo.c:123, 6 bytes)
End: Overflown (magic=0x2A8FCC00 instead of 0x2A8FCC84)
1 byte(s) overflown
-------------------------------------foo.c(125)
: Block 0x08219C40 status:
Beginning: OK (allocated on foo.c:123, 6 bytes)
End: Overflown (magic=0x2A8FCC00 instead of 0x2A8FCC84)
1 byte(s) overflown
---------------------------------------
The warning shows where the overflowed memory was allocated (line 123) and
where this overflow was detected (line 125 in the efree( ) call).
These memory-handling functions can catch a lot of silly little mistakes that might
otherwise waste your time, so do your development with the debug switch enabled.
Don’t forget to recompile in non-debug mode when you are done testing, though, as
the various tests done by the emalloc( ) type functions slow down PHP.
An extension compiled in debug mode does not work in an instance of PHP not
compiled in debug mode. When PHP loads an extension, it checks to see if the
debug setting, the thread-safety setting, and the API version all match. If something
doesn’t match, you will get a warning like this:
Warning: foo: Unable to initialize module
Module compiled with debug=0, thread-safety=0 module API=20010901
PHP compiled with debug=1, thread-safety=0 module API=20010901
330 | Chapter 14: Extending PHP
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