Libgccjit AOT Codegen for Rustc | Hacker News Reader

Libgccjit AOT Codegen for Rustc

github.com

113 pointsvarbhat13 comments

This backend is now sufficiently mature that the Rust Compiler Team is discussing upstreaming it (just the Rust part, not libgccjit itself): https://github.com/rust-lang/compiler-team/issues/442

This is very cool, I'd like to see more projects using libgccjit because it's much, MUCH nicer than the usual approach of building your frontend alongside GCC. I think it's the first step towards a modular GCC, which is an absolute necessity for it to stay relevant in an LLVM-dominated world.

I find libgccjit also way more clear and easy to use than LLVM for code compilation and execution. There is not to many functions to keep track off. The 'goto' centric code generation is nice to wrap your head around.

The qrintf preprocessor accelerates sprintf expressions. https://github.com/h2o/qrintf

Noob question: Can libgccjit be used to do the same at runtime?

Yes. You can compile arbitrary code at runtime. You can "extract" a function generated with libgccjit as a function pointer and use it in your static code.

And the great think about this, compared to static code, is you can compile runtime data into this code if you want. So instead of storing something like a configuration value in a global variable which you then have to read, you can store it in the code!

libgccjit looks good. Is it still bound to the GPL license?

As far as I can tell, yes. There is a "GPL licensed" footer at the bottom of the libgccjit page[0].

[0]: https://gcc.gnu.org/wiki/JIT

And as the FSF has stopped requiring copyright assignments, their hands are bound for the future. If it turns out that something like LGPL is better in the long term, there is no chance for a relicensing in the future.

That change came from the GCC steering committee, not the FSF.

This mostly matters for code contributions, correct? Does dynamically linking to libgccjit.so trigger the GPL requirements for the linking code?

Does dynamically linking to libgccjit.so trigger the GPL requirements for the linking code?

Yes, the GPL triggers if you distribute programs that merely link against a thusly licensed library - at least that's the intention.

Full disclosure, there are people who disagree with the FSF's interpretation, arguing that merely linking to a library doesn't necessarily create a derivative work. I don't know if that has ever been tested in a court of law...

Thanks, I was alluding to the libgcc license, which has an exception for dynamic linking. But it appears libgccjit is GPL3 without the exception, like the rest of core GCC.

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