As of version 4.1, HookCase now supports watchpoints. This is useful for finding out which functions write to a particular location in memory -- for example the "sideband buffer" that's used to implement accelerated OpenGL graphics.
The watchpoint example Examples/watchpoints
contains two sets of hooks. One implements a trivial example of
watchpoint use, for purposes of illustration and testing. The other
shows how watchpoints can be used to reverse engineer the sideband
buffer. The first hook works on any system with any application. The
second (and more interesting) set of hooks only works on systems with
hardware acceleration, and in applications that use OpenGL (for
example Firefox and Chrome, but not Safari).
Build the example using make, then use it with a recent Firefox
Nightly to see how it works. (Firefox and Chrome releases have their
symbols stripped, but Firefox Nightlies don't. So stack traces of
Firefox Nightlies contain much more information.)
HC_INSERT_LIBRARY=/full/path/to/hook.dylib "/Applications/Firefox Nightly.app/Contents/MacOS/firefox"
Firefox Nightlies are available for download here.