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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Wed, 17 Aug 2022 17:24:30 +0200
Message-ID: <CAK8P3a2YuGsSJY2-=npqXMHXEr+zaF36iDrM+kP=9nS85FLpbA@mail.gmail.com>
Subject: Re: [PATCH v8 27/31] Kbuild: add Rust support
To:     Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Cc:     Arnd Bergmann <arnd@arndb.de>, Miguel Ojeda <ojeda@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
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On Wed, Aug 17, 2022 at 5:13 PM Miguel Ojeda
<miguel.ojeda.sandonis@gmail.com> wrote:
> On Wed, Aug 17, 2022 at 4:40 PM Arnd Bergmann <arnd@arndb.de> wrote:
> >
> > I tried enabling rust support in the gcc builds I provide at
> > https://mirrors.edge.kernel.org/pub/tools/crosstool/files/bin/arm64/12.1.0/
>
> Thanks for giving it a go!
>
> > to make this more accessible, but it appears that the command line
> > options here are not portable:
> >
> >  /home/arnd/cross/x86_64/gcc-12.1.0+rust-nolibc/x86_64-linux/bin/x86_64-linux-gccrs
>
> So you mean with GCC Rust, right? (i.e. we have "GCC builds" working,
> via compiling the Rust side with LLVM and linking with the GCC C side,
> but it is not intended for production or to be supported, even if we
> cover it in our CI, test it boots and loads modules etc.).

Yes, I meant GCC rust, with the contents of
https://gcc.gnu.org/git/?p=gcc.git;a=shortlog;h=refs/heads/devel/rust/master
merged into the gcc-12.1.0 release tag.

> > I guess nobody has tried this so far. Would you think that fixing this is only
> > a matter for fixing the build system to pass the correct flags depending on the
> > compiler, or is this broken in a more fundamental way?
>
> If you meant GCC Rust, then it is a bit too early for the compiler. As
> far as I now, they are working on compiling the `core` crate and
> supporting more stable language features. They are also researching
> the integration of the borrow checker, though we wouldn't need that
> for "only" compiling the kernel.
>
> Now, if they decided to focus on supporting Rust for Linux early on
> (which would be great), they would still need to work on the delta
> between what what they target now and what we use (which includes both
> stable and some unstable features), plus I assume infrastructure bits
> like the platform (target spec) support, the flags / `rustc` driver
> (though I would be happy to do as much as possible on our side to
> help), etc.
>
> (We privately talked about possible timelines for all that if they
> were to focus on Rust for Linux etc., but I let them comment or not on
> that... Cc'ing them! :)

Thanks for the explanation. My hope was that building the kernel
would actually be easier here than building the more complicated
rust user space.

The gcc cross-compilers on kernel.org are similarly easy to build for
all architectures the kernel supports because the complexity is
usually in picking a working libc for the more obscure architectures,
so I was naively thinking that this would work for building the
rust support across all architectures in Linux.

I tried one more step and just removed the unsupported command
line flags to see what would happen, but that did not get me any
further:

/home/arnd/cross/x86_64/gcc-12.1.0+rust-nolibc/x86_64-linux/bin/x86_64-linux-gccrs
-frust-edition=2021 -Dunsafe_op_in_unsafe_fn -Drust_2018_idioms
-Dunreachable_pub -Dnon_ascii_idents
-Drustdoc::missing_crate_level_docs -Dclippy::correctness
-Dclippy::style -Dclippy::suspicious -Dclippy::complexity
-Dclippy::perf -Dclippy::let_unit_value -Dclippy::mut_mut
-Dclippy::needless_bitwise_bool -Dclippy::needless_continue  -O
/git/arm-soc/scripts/generate_rust_target.rs; mv
scripts/generate_rust_target.d scripts/.generate_rust_target.d; sed -i
'/^#/d' scripts/.generate_rust_target.d
rust1: internal compiler error: Segmentation fault
0x7f37ee04b51f ???
./signal/../sysdeps/unix/sysv/linux/x86_64/libc_sigaction.c:0
0x7f37ee032fcf __libc_start_call_main
../sysdeps/nptl/libc_start_call_main.h:58
0x7f37ee03307c __libc_start_main_impl
../csu/libc-start.c:409
Please submit a full bug report, with preprocessed source (by using
-freport-bug).
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.

      Arnd