sparc-unknown-none-elf

Tier: 3

Rust for bare-metal 32-bit SPARC V7 and V8 systems, e.g. the Gaisler LEON3.

Target	Descriptions
sparc-unknown-none-elf	SPARC V7 32-bit (freestanding, hardfloat)

Target maintainers

@jonathanpallant

Requirements

This target is cross-compiled. There is no support for std. There is no default allocator, but it's possible to use alloc by supplying an allocator.

By default, code generated with this target should run on any SPARC hardware; enabling additional target features may raise this baseline.

• -Ctarget-cpu=v8 adds the extra SPARC V8 instructions.

• -Ctarget-cpu=leon3 adds the SPARC V8 instructions and sets up scheduling to suit the Gaisler Leon3.

Functions marked extern "C" use the standard SPARC architecture calling convention.

This target generates ELF binaries. Any alternate formats or special considerations for binary layout will require linker options or linker scripts.

Building the target

You can build Rust with support for the target by adding it to the target list in bootstrap.toml:

[build]
build-stage = 1
host = ["<target for your host>"]
target = ["<target for your host>", "sparc-unknown-none-elf"]

Replace <target for your host> with x86_64-unknown-linux-gnu or whatever else is appropriate for your host machine.

Building Rust programs

To build with this target, pass it to the --target argument, like:

cargo build --target sparc-unknown-none-elf

This target uses GCC as a linker, and so you will need an appropriate GCC compatible sparc-unknown-none toolchain. The default linker binary is sparc-elf-gcc, but you can override this in your project configuration, as follows:

.cargo/config.toml:

[target.sparc-unknown-none-elf]
linker = "sparc-custom-elf-gcc"

Testing

As sparc-unknown-none-elf supports a variety of different environments and does not support std, this target does not support running the Rust test suite.

Cross-compilation toolchains and C code

This target was initially tested using BCC2 from Gaisler, along with the TSIM Leon3 processor simulator. Both BCC2 GCC and BCC2 Clang have been shown to work. To work with these tools, your project configuration should contain something like:

.cargo/config.toml:

[target.sparc-unknown-none-elf]
linker = "sparc-gaisler-elf-gcc"
runner = "tsim-leon3"

[build]
target = ["sparc-unknown-none-elf"]
rustflags = "-Ctarget-cpu=leon3"

With this configuration, running cargo run will compile your code for the SPARC V8 compatible Gaisler Leon3 processor and then start the tsim-leon3 simulator. The libcore was pre-compiled as part of the rustc compilation process using the SPARC V7 baseline, but if you are using a nightly toolchain you can use the -Z build-std=core option to rebuild libcore from source. This may be useful if you want to compile it for SPARC V8 and take advantage of the extra instructions.

.cargo/config.toml:

[target.sparc-unknown-none-elf]
linker = "sparc-gaisler-elf-gcc"
runner = "tsim-leon3"

[build]
target = ["sparc-unknown-none-elf"]
rustflags = "-Ctarget-cpu=leon3"

[unstable]
build-std = ["core"]

Either way, once the simulator is running, simply enter the command run to start the code executing in the simulator.

The default C toolchain libraries are linked in, so with the Gaisler BCC2 toolchain, and using its default Leon3 BSP, you can use call the C putchar function and friends to output to the simulator console. The default linker script is also appropriate for the Leon3 simulator, so no linker script is required.

Here's a complete example using the above config file:

#![no_std]
#![no_main]

extern "C" {
    fn putchar(ch: i32);
    fn _exit(code: i32) -> !;
}

#[no_mangle]
extern "C" fn main() -> i32 {
    let message = "Hello, this is Rust!";
    for b in message.bytes() {
        unsafe {
            putchar(b as i32);
        }
    }
    0
}

#[panic_handler]
fn panic(_panic: &core::panic::PanicInfo) -> ! {
    unsafe {
        _exit(1);
    }
}

$ cargo run --target=sparc-unknown-none-elf
   Compiling sparc-demo-rust v0.1.0 (/work/sparc-demo-rust)
    Finished dev [unoptimized + debuginfo] target(s) in 3.44s
     Running `tsim-leon3 target/sparc-unknown-none-elf/debug/sparc-demo-rust`

 TSIM3 LEON3 SPARC simulator, version 3.1.9 (evaluation version)

 Copyright (C) 2023, Frontgrade Gaisler - all rights reserved.
 This software may only be used with a valid license.
 For latest updates, go to https://www.gaisler.com/
 Comments or bug-reports to support@gaisler.com

 This TSIM evaluation version will expire 2023-11-28

Number of CPUs: 2
system frequency: 50.000 MHz
icache: 1 * 4 KiB, 16 bytes/line (4 KiB total)
dcache: 1 * 4 KiB, 16 bytes/line (4 KiB total)
Allocated 8192 KiB SRAM memory, in 1 bank at 0x40000000
Allocated 32 MiB SDRAM memory, in 1 bank at 0x60000000
Allocated 8192 KiB ROM memory at 0x00000000
section: .text, addr: 0x40000000, size: 20528 bytes
section: .rodata, addr: 0x40005030, size: 128 bytes
section: .data, addr: 0x400050b0, size: 1176 bytes
read 347 symbols

tsim> run
  Initializing and starting from 0x40000000
Hello, this is Rust!

  Program exited normally on CPU 0.
tsim>