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GCC and Python

When writing an earlier post, I realized I haven’t yet written about the Python plugin for GCC.

This is awesome! It is by far the simplest way to write a GCC plugin. The primary reason is that the author, the amazing David Malcolm, has put a lot of effort into the polish: this plugin is the simplest one to build (“make” works for me, with the Fedora 15 system GCC) and also the one with the best documentation.

Why would you want to write a plugin? Pretty much every program — and especially every C program, as C has such bad metaprogramming support — has rules which cannot be expressed directly in the language. One usually resorts to various tricks, and in extremis patch review by all-knowing maintainers, to preserve these. The plugin offers another way out: write a Python script to automate the checking.

I’ve already written a couple of custom checkers for use on GDB (which is a very idiosyncratic C program, basically written in an oddball dialect of C++), which have found real bugs.  These checkers cover things that no generic static analysis tool would ever correctly check, e.g., for the proper use of GDB’s exception handling system.  The exception checker, which we use to verify that we’re correctly bridging between Python’s exception system and GDB’s, took less than a day to write.

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