Arm support

[sevenautumns]

Added Arm support to this project.

I used a new Rust target armv7-unknown-l4re-uclibceabihf for compiling the code.
For this I bootstrapped the Rust compiler: https://github.com/Steav005/rust/tree/update-l4re-target

using make setup, selecting arm-virt-pl2 and make works flawlessly.
Running make qemu PLATFORM_TYPE=arm_virt afterwards in obj/l4/arm-v7 also works.
Both examples basic_ipc (Rust) and hello_shared (C) seem to run.
(Of course all of this still works for amd64 as well)

Made this into a draft because currently I am using my own patch of libc:
https://github.com/Steav005/libc

Ill change this into a proper Pull Request once I created a pull request for libc to integrate my changes.

[humenda]

I used a new Rust target `armv7-unknown-l4re-uclibceabihf` for compiling the code. For this I bootstrapped the Rust compiler: https://github.com/Steav005/rust/tree/update-l4re-target

I see. We might want to upstream this once we've merged here.

Ill change this into a proper Pull Request once I created a pull request for [libc](https://github.com/rust-lang/libc) to integrate my changes.

Ok, sounds good. Please upstream libc as you said and hopefully we got your other change merged until then. Thanks

[humenda]

Can we try to make progress on this? I'm preparing patches for aarch64, depending on your response, you might want to rebase your work on top of this.

[sevenautumns]

It looks like libc is not going to pull my libc changes, because the libc code of mine would only be relevant for a custom rust-toolchain.
So unless the rust compiler gets support for l4re on arm and l4bender, they will probably not merge.
This makes this pull request or at least the rust code in this PR reliant on my custom libc repo. I do not know if this is okay with you.

[humenda]

So unless the rust compiler gets support for l4re on arm and l4bender, they will probably not merge.

I see their point. For my aarch64-specific stuff, I've patched libc, i.e. replaced `libc =` with a path local in the repo for all Rust crates. Is there a way to conditionally patch dependencies, i.e. for aarch64/aarch32, use x, but for everything else y? I'm afraid that this is not possible at the level of Cargo.toml.

[humenda]

I've looked at the code that I wrote recently and I used an abstraction. I'm currently reworking the code and cleaning it up. Please have a look at the (temporary feature branch) [aarch64](https://github.com/humenda/rustl4re/tree/aarch64/src/l4/pkg/l4rust/core-ffi-helpers). I already reworked l4-sys-rust to rely on core-ffi-helpers which makes it work for x86_64 (libc) and aarch64 (custom types). What do you think? If you deems this useful, I'd merge those commits to master and you could rebase your changes onto master to also use core-ffi-helpers and avoid the patched libc version.

[sevenautumns]

I've looked at the aarch64 branch and I like the Idea with the core-ffi-helpers.
I've also made a first effort to make my arm branch compatible with the core-ffi-helpers instead of my patched version of the libc-library, which seems to work just fine.
Once you merge your aarch64 branch into master, I'll update this pull request to be compatible.

[sevenautumns]

Did you already add an aarch64 target for l4re to your rust-toolchain?
Maybe I can create a pull request for my arm target over there too.

[humenda]

Hi @Steav005

I am aware that after this time, one could have regarded this as abandoned.
However, I finally have found the time too resume the work. I have cherry-picked
the first 2 commits and they are on master. I will go ahead in the next days /
weeks and review the commits individually, as the changes are too big to be
rerviewed at once. Given that I made you wait for so long, it's my obligation to
split up the PR :).