An ag(e)ing hacker, Luca Saiu's blog
2022-03-10 21:32 Luca Saiu

GNU Jitter and GCC: the fun of playing with fire

A few days ago on March 6 I participated in the Binary T00ls Summit online event ( organised by José Marchesi (; a video recording is now available.

My presentation had the ridiculous title GNU Jitter and the illusion of simplicity or Copying, patching and combining compiler-generated code in executable memory or The Anarchist’s guide to GCC or The fun of playing with fire — or, in shortened form, GNU Jitter and GCC: the fun of playing with fire.

This is the official abstract:

GNU Jitter is a generator of portable and efficient language virtual machines; a Jittery VM lies at the heart of GNU poke. Jitter achieves high performance by first machine-generating C code, then compiling the generated code ahead-of-time with GCC, and finally copying, patching and recombining pieces of native code at run time into executable memory. GCC was definitely not designed for this task.
In this talk about the inner workings of Jitter I will show how to coerce the compiler into generating code suitable for run-time replication and how to maintain correctness, without the user noticing, when GCC optimisations play against us. In a task where many have failed before I believe I can now show a recipe for success.

I published a copy of the video recording on the Internet Archive: see You can find a slightly updated copy of my PDF slides on my web site at

I wish to thank José, who gracefully took care of editing all video recordings including mine, and the other participants for their interest.

The Binary T00ls Summit 2022 was a pleasant and interesting event.

— Luca Saiu, 2022-03-10 21:32

binary-t00ls-summit, free-software, gnu, hacking, jitter, myself

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