Progress Report #26: rustc_codegen_gcc can now compile Rust for Linux!

01 Oct 2023

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

This month, I did the following commits, which are yet to be sent on the gcc mailing list:

State of rustc_codegen_gcc

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

It was announced last year that rustc_codegen_gcc can compile Rust for Linux with very few hacks. Today, I’m happy to announce that it can compile Rust for Linux without any patches! (Well, we still need patches to GCC itself like the rest of rustc_codegen_gcc, but those will be merged upstream eventually.)

State of compiling popular crates

It was asked from time to time to test compiling the most popular crates with rustc_codegen_gcc and I finally did so. Here are the results of running the tests of the most popular crates.

Project	Compiles	Tests passing	Tests failing	Note
getrandom
memchr

cfg-if
lazy_static
base64				The process consumes a lot of memory and gets OOM-killed if running all the tests at once.



regex
bitflags
serde

As you can see, rustc_codegen_gcc successfully run and pass all the tests of all those crates. I had to fix a few small bugs in order to achieve this result and they were merged last month. The tests from base64 seem to have a memory leak when using the GCC codegen: I’m going the investigate this issue in the future.

In addition to running those tests, I was able to successfully run process-viewer and it seemed to work properly.

Next month, I plan to continue working on correctly handling the endianness for non-native 128-bit integers. This month, I setup the CI to be able to cross-compile to the m68k architecture in order to be able to run the integers test.

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

Feature	Last month completion	Completion	Delta
Unwinding.

More function and variable attributes.
Target features (to detect what is supported in an architecture, like SIMD).
Thin LTO.
Debug info.
Endianness support for non-native 128-bit integers.
Rustup distribution.
SIMD for other architectures than x86-64.
Support for new architectures in libraries (libc, object, …) and rustc.
SIMD (x86-64).
Basic and aggregate types.
Operations, local and global variables, constants, functions, basic blocks.
Atomics.
Thread-local storage.
Inline assembly.
Many intrinsics.
Metadata.
Setting optimization level.
Packed structures.
Alignment, symbol visibility, attributes.
128-bit integers.

How to contribute

`rustc_codegen_gcc`

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

Run the tests locally.
Choose a test that fails.
Investigate why it fails.
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.

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
saethlin
embark-studios
Traverse-Research
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. Another big thank you to Commeownist for his contributions.

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

0x7CFE
oleid
acshi
joshtriplett
sdroege
alanfalloon
steven-joruk
davidlattimore
colelawrence
zmanian
alexkirsz
berkus
belzael
Shoeboxam
yerke
seanpianka
srijs
kkysen
riking
Lemmih
memoryruins
senden9
robjtede
Jonas Platte
spike grobstein
Oliver Marshall
Sam Harrington
Jonas
Jeff Muizelaar
Eugene Bulkin
Chris Butler
sierrafiveseven
Joseph Garvin
MarcoFalke
athre0z
icewind
Tommy Thorn
Sebastian Zivota
Oskar Nehlin
Nicolas Barbier
Daniel
Thomas Colliers
Justin Ossevoort
Chris
Bálint Horváth
kiyoshigawa
robinmoussu
Daniel Sheehan
Marvin Löbel
nacaclanga
Matthew Conolly
0x0177b11f
L.apz
JockeTF
davidcornu
stuhood
Myrik Lord
Mauve
icewind1991
nicholasbishop
Emily A. Bellows
David Vasak
Eric Driggers
Olaf Leidinger
UtherII
simonlindholm
lemmih
Eddddddd
rrbutani
Mateusz K
0xdeafbeef

and a few others who preferred to stay anonymous.

Former sponsors/patreons:

finfet
Alovchin91
mexus
raymanfx
ghost
gilescope
olanod
Denis Zaletaev
Chai T. Rex
Paul Ellenbogen
Dakota Brink
Botlabs
Oliver Marshall
pthariensflame
tedbyron
sstadick
Absolucy
rafaelcaricio
dandxy89
luizirber
regiontog
vincentdephily
Hofer-Julian
messense
fanquake
jam1garner
sbstp
evanrichter
Nehliin
nevi-me
TimNN

Progress Report #26: rustc_codegen_gcc can now compile Rust for Linux!