Rust for RTEMS [was: Re: Interested for GSoC 2023]

[Karel Gardas]

On 2/27/23 12:00, Karel Gardas wrote:
>>> On 2/27/23 02:16, Joel Sherrill wrote:
>>>> Another GCC related project could be Rust RTEMS Support but I don't
>>>> know what that entails beyond turning it on and seeing what goes
>>>> wrong. I tried to build it last year and got far enough to decide to
>>>> wait before trying again.
>>>
>>> Not sure how far you went. The process is generally:
>>>
>>> (1) tune Rust compiler to cross-compile correctly for specific 
>>> hardware/os
>>> platform. So basically you get no_std capable compiler
>>>
>>> (2) review, patch and by using (1) cross-compile libc
>>>
>>> (3) using sources from (1) and (2) build full stage (std enabled) rustc.
>>>
>>> (4) tweak and tune tools (rustup/cargo etc.) whenever required to smooth
>>> sharp edges for RTEMS.
>>>
>>> Here, I'm nearly finished with (1) for arm-rtems (e.g. cortex-aX not 
>>> cortex-
>>> mX).

Something is running:

silence:/tmp$ cat hello-rtems.rs

#![no_std]
#![no_main]

use core::panic::PanicInfo;
use core::ffi::c_char;
use core::ffi::c_int;

extern "C" {
     fn puts(str: *const c_char) -> c_int;
}

#[no_mangle]
pub fn main() -> ! {
     unsafe {
         puts(b"Rust says hello to hosting RTEMS\n\0".as_ptr() as *const 
i8);
     }
     loop {}
}

#[panic_handler]
fn panic(_: &PanicInfo) -> ! {
   loop {}
}

silence:/tmp$ /tmp/rustc-rtems-arm/bin/rustc -g -Z verbose 
--target=arm-rtems hello-rtems.rs -lrtemscpu -lrtemsbsp -lrtemsdefaultconfig

silence:/tmp$ file hello-rtems.exe
hello-rtems.exe: ELF 32-bit LSB executable, ARM, EABI5 version 1 (SYSV), 
statically linked, with debug_info, not stripped

silence:/tmp$ ~rtems/sfw/qemu-7.2.0/bin/qemu-system-arm -serial null 
-serial mon:stdio -nographic -M xilinx-zynq-a9 -m 512M -kernel 
/tmp/hello-rtems.exe
Rust says hello to hosting RTEMS

QEMU 7.2.0 monitor - type 'help' for more information
(qemu) q
silence:/tmp$


Note: this is hacked rust-lang.org rust compiler, not gccrs project and 
soon to be released GCC 13.

The biggest problem and probably soon to be source of headaches is 
mixture of LLVM's compiler-rt and GCC's libgcc binaries. This means once 
you employ for example arithmetic you need to add
-C link-arg=-Wl,--allow-multiple-definition otherwise you would get 
multiple definitions symbols error.

Karel