rustc_codegen_gcc: Progress Report #43

What is rustc_codegen_gcc?

rustc_codegen_gcc is a GCC ahead-of-time codegen for rustc, meaning that it can be loaded by the existing rustc frontend, but benefits from GCC by having more architectures supported and having access to GCC’s optimizations. It is not to be confused with gccrs, which is a GCC frontend for Rust.

GCC patches status

There’s been some progress on this side!

Not much progress for reviews or merge upstream, but we wrote many more patches in our GCC fork:

State of rustc_codegen_gcc

Here’s what has been done during the past months:

I’m happy to have finally fixed the issues we had with unwinding when compiling in release mode! However, the version of rustc_codegen_gcc distributed by rustup does not contain that fix yet since we had a lot of issues with syncing the changes to the Rust repo. Most of those issues should be fixed now, so we should be able to sync soon.

While I consider unwinding to be done in rustc_codegen_gcc, there will probably be some issues to fix outside rustc_codegen_gcc. For instance, we had to fix an issue in the Rust unwind library. We will probably also need to fix some exception handling issues in some GCC backends.

Now that unwinding is fixed, it is a good time to do a crater run to discover issues with rustc_codegen_gcc and see how many crates it supports. Before we do that, though, I plan to attempt to compile a couple widely-used crates to see if there are big issues to fix first. So, this is what I plan to do in the coming months.

Here’s a rough summary of what has been implemented:

Feature Last month completion Completion Delta

Unwinding.

80%

100%

+20%

Run tests in the Rust CI

80%

80%

More function and variable attributes.

22%

60%

+38%

Target features (to detect what is supported in an architecture, like SIMD).

82%

82%

Debug info.

20%

20%

Thin LTO.

5%

5%

Support for new architectures in libraries (libc, object, …) and rustc.

2%

2%

SIMD for other architectures than x86-64.

0%

Refactor to rustc_codegen_ssa to make it easier for the GCC codegen

0%

Rustup distribution.

Done

LTO

Done

Endianness support for non-native 128-bit integers.

Done

SIMD (x86-64).

Done

Basic and aggregate types.

Done

Operations, local and global variables, constants, functions, basic blocks.

Done

Atomics.

Done

Thread-local storage.

Done

Inline assembly.

Done

Many intrinsics.

Done

Metadata.

Done

Setting optimization level.

Done

Packed structures.

Done

Alignment, symbol visibility, attributes.

Done

128-bit integers.

Done

UI tests progress

Here are the results of running the UI tests in the CI:

Category Last Month This Month Delta

Passed

7156

7699

+543

Failed

80

21

-59

How to contribute

rustc_codegen_gcc

If you want to help on the project itself, please do the following:

  1. Run the tests locally.

  2. Choose a test that fails.

  3. Investigate why it fails.

  4. Fix the problem.

Even if you can’t fix the problem, your investigation could help, so if you enjoy staring at assembly code, have fun!

Crates and rustc

If you would like to contribute on adding support for Rust on currently unsupported platforms, you can help by adding the support for those platforms in some crates like libc and object and also in the rust compiler itself.

Test this project

Otherwise, you can test this project on new platforms and also compare the assembly with LLVM to see if some optimization is missing.

To do so, follow these instructions to build the project and run a program via the cargo command of our script.

If you find a bug, please open an issue.

Good first issue

Finally, another good way to help is to look at good first issues. Those are issues that should be easier to start with.

Thanks for your support!

I wanted to personally thank all the people that sponsor this project: your support is very much appreciated.

A special thanks to the following sponsors:

  • Futurewei

  • Shnatsel

  • Rust Foundation

A big thank you to bjorn3 for his help, contributions and reviews. And a big thank you to lqd and GuillaumeGomez for answering my questions about rustc’s internals and to Kobzol and GuillaumeGomez for their contributions. Another big thank you to Commeownist for his contributions.

Also, a big thank you to the rest of my sponsors:

  • kpp

  • 0x7CFE

  • oleid

  • joshtriplett

  • djc

  • sdroege

  • pcn

  • alanfalloon

  • davidlattimore

  • colelawrence

  • zmanian

  • berkus

  • belzael

  • yvt

  • yerke

  • srijs

  • kkysen

  • riking

  • Lemmih

  • memoryruins

  • senden9

  • robjtede

  • Jonas Platte

  • Sam Harrington

  • Jonas

  • Eugene Bulkin

  • Joseph Garvin

  • MarcoFalke

  • athre0z

  • Sebastian Zivota

  • Oskar Nehlin

  • Nicolas Barbier

  • Daniel

  • Justin Ossevoort

  • kiyoshigawa

  • Daniel Sheehan

  • Marvin Löbel

  • nacaclanga

  • L.apz

  • JockeTF

  • davidcornu

  • stuhood

  • Mauve

  • icewind1991

  • nicholasbishop

  • David Vasak

  • Eric Driggers

  • Olaf Leidinger

  • UtherII

  • simonlindholm

  • lemmih

  • Eddddddd

  • rrbutani

  • Mateusz K

  • thk1

  • teh

  • KirilMihaylov

  • Vladislav Sukhmel

  • ximou

  • Kate Kiesel

  • jplatte

  • thesamesam

  • sbstp

  • Laine Taffin Altman

  • LunNova

  • Robin Moussu

and a few others who preferred to stay anonymous.

Former sponsors/patreons:

  • igrr

  • embark-studios

  • saethlin

  • Traverse-Research

  • finfet

  • Alovchin91

  • wezm

  • mexus

  • raymanfx

  • ghost

  • gilescope

  • olanod

  • Denis Zaletaev

  • Chai T. Rex

  • Paul Ellenbogen

  • Dakota Brink

  • Botlabs

  • Cass

  • Oliver Marshall

  • pthariensflame

  • tedbyron

  • sstadick

  • Absolucy

  • rafaelcaricio

  • dandxy89

  • luizirber

  • regiontog

  • vincentdephily

  • zebp

  • Hofer-Julian

  • messense

  • fanquake

  • jam1garner

  • evanrichter

  • Nehliin

  • nevi-me

  • TimNN

  • steven-joruk

  • seanpianka

  • spike grobstein

  • Jeff Muizelaar

  • robinmoussu

  • Chris Butler

  • sierrafiveseven

  • icewind

  • Thomas Colliers

  • Tommy Thorn

  • Bálint Horváth

  • Matthew Conolly

  • Lapz

  • Myrik Lord

  • T

  • Emily A. Bellows

  • Chris

  • repi

  • opensrcsec

  • NobodyXu

  • alexkirsz

  • 0xdeafbeef

  • l-const

  • CohenArthur

  • bes

  • acshi

  • Shoeboxam

  • teohhanhui

  • g4titanx

  • 0x0177b11f

  • VasanthakumarV