Raspberry Pi Bare Bones Rust: Difference between revisions

{{FirstPerson}}

{{BeginnersWarning}}

{{Rating|3}}

In the C tutorial, you created a reference to a symbol "kernel_main" in boot.S.

 

// Call kernel_main

ldr r3, =kernel_main

 

At the end of that tutorial, the compiled kernel.c object file kernel.o provided a definition for this symbol using its function "kernel_main" to the linker when creating kernel.elf.

For brevity we will assume our environment has no Rust installation.

 

 

This installs rustup, which will manage the Rust compiler and Cargo.

 

 

We will need to recompile some of the Rust language later, so we need this component.

 

 

We will use [https://github.com/japaric/xargo xargo] to build our project, which works just like a drop-in replacement for Cargo. xargo automatically handles the significant task of compiling and linking in components of the Rust language we will need (such as libcore.rs) for our target.

 

xargo new kernel

cd kernel

rustup override set nightly

 

This creates our crate and tells rustup to use the nightly Rust toolchain for it. We will need features of Rust that are not available in stable.

In this directory create a file called arm-none-eabihf.json with this content:

 

{

"llvm-target": "arm-none-eabihf",

"no-compiler-rt": true

}

 

Rust uses LLVM as a backend, which expects this kind of specification file for non-standard (has no triple) compilation targets. Filling out the values of this is beyond the scope of this tutorial; more information can be found in [https://github.com/japaric/rust-cross rust-cross] which covers cross compiling Rust in detail.

</pre>

 

 

Now, revisit the command which built kernel.elf in the C tutorial, but instead of kernel.o, provide the libkernel.rlib xargo just built in the target directory.

 

 

This is it! You've built Rust code for bare metal arm that will run on the Raspberry Pi!

If you run this you will see your text printed out on the virtual serial port:

 

qemu-system-arm -M raspi2 -kernel myos.elf -serial stdio

 

====External Resources====