Rollup merge of #114006 - jonathanpallant:update-sparc-unknown-readme, r=Amanieu
Update sparc-unknown-none-elf platform README Cherry picked a couple of commits that didn't quite make it in #113535
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@ -17,13 +17,6 @@ Rust for bare-metal 32-bit SPARC V7 and V8 systems, e.g. the Gaisler LEON3.
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This target is cross-compiled. There is no support for `std`. There is no
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default allocator, but it's possible to use `alloc` by supplying an allocator.
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This allows the generated code to run in environments, such as kernels, which
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may need to avoid the use of such registers or which may have special
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considerations about the use of such registers (e.g. saving and restoring them
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to avoid breaking userspace code using the same registers). You can change code
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generation to use additional CPU features via the `-C target-feature=` codegen
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options to rustc, or via the `#[target_feature]` mechanism within Rust code.
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By default, code generated with this target should run on any `SPARC` hardware;
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enabling additional target features may raise this baseline.
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@ -46,20 +39,31 @@ list in `config.toml`:
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```toml
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[build]
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build-stage = 1
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target = ["sparc-unknown-none-elf"]
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host = ["<target for your host>"]
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target = ["<target for your host>", "sparc-unknown-none-elf"]
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```
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Replace `<target for your host>` with `x86_64-unknown-linux-gnu` or whatever
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else is appropriate for your host machine.
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## Building Rust programs
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```text
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To build with this target, pass it to the `--target` argument, like:
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```console
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cargo build --target sparc-unknown-none-elf
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```
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This target uses GCC as a linker, and so you will need an appropriate GCC
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compatible `sparc-unknown-none` toolchain.
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compatible `sparc-unknown-none` toolchain. The default linker binary is
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`sparc-elf-gcc`, but you can override this in your project configuration, as
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follows:
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The default linker name is `sparc-elf-gcc`, but you can override this in your
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project configuration.
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`.cargo/config.toml`:
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```toml
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[target.sparc-unknown-none-elf]
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linker = "sparc-custom-elf-gcc"
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```
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## Testing
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@ -81,6 +85,26 @@ something like:
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linker = "sparc-gaisler-elf-gcc"
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runner = "tsim-leon3"
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[build]
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target = ["sparc-unknown-none-elf"]
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rustflags = "-Ctarget-cpu=leon3"
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```
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With this configuration, running `cargo run` will compile your code for the
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SPARC V8 compatible Gaisler Leon3 processor and then start the `tsim-leon3`
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simulator. The `libcore` was pre-compiled as part of the `rustc` compilation
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process using the SPARC V7 baseline, but if you are using a nightly toolchain
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you can use the
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[`-Z build-std=core`](https://doc.rust-lang.org/cargo/reference/unstable.html#build-std)
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option to rebuild `libcore` from source. This may be useful if you want to
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compile it for SPARC V8 and take advantage of the extra instructions.
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`.cargo/config.toml`:
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```toml
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[target.sparc-unknown-none-elf]
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linker = "sparc-gaisler-elf-gcc"
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runner = "tsim-leon3"
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[build]
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target = ["sparc-unknown-none-elf"]
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rustflags = "-Ctarget-cpu=leon3"
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@ -89,16 +113,16 @@ rustflags = "-Ctarget-cpu=leon3"
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build-std = ["core"]
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```
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With this configuration, running `cargo run` will compile your code for the
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SPARC V8 compatible Gaisler Leon3 processor and then start the `tsim-leon3`
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simulator. Once the simulator is running, simply enter the command
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`run` to start the code executing in the simulator.
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Either way, once the simulator is running, simply enter the command `run` to
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start the code executing in the simulator.
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The default C toolchain libraries are linked in, so with the Gaisler [BCC2]
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toolchain, and using its default Leon3 BSP, you can use call the C `putchar`
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function and friends to output to the simulator console.
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function and friends to output to the simulator console. The default linker
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script is also appropriate for the Leon3 simulator, so no linker script is
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required.
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Here's a complete example:
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Here's a complete example using the above config file:
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```rust,ignore (cannot-test-this-because-it-assumes-special-libc-functions)
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#![no_std]
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