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Mention RUST_TARGET_PATH in Set Up Rust post (first edition) (#416)

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Philipp Oppermann
2018-03-13 16:39:32 +01:00
committed by GitHub
parent af151a2d45
commit 59f5e4fe17
1 changed files with 7 additions and 5 deletions
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blog/content/posts/03-set-up-rust/index.md
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@@ -192,10 +192,12 @@ However, the large SIMD registers lead to problems in OS kernels. The reason is
As noted above, floating point operations on `x86_64` use SSE registers, so floats are no longer usable without SSE. Unfortunately, the Rust core library already uses floats (e.g., it implements traits for `f32` and `f64`), so we need an alternative way to implement float operations. The `soft-float` feature solves this problem by emulating all floating point operations through software functions based on normal integers. As noted above, floating point operations on `x86_64` use SSE registers, so floats are no longer usable without SSE. Unfortunately, the Rust core library already uses floats (e.g., it implements traits for `f32` and `f64`), so we need an alternative way to implement float operations. The `soft-float` feature solves this problem by emulating all floating point operations through software functions based on normal integers.
### Compiling ### Compiling
To build our kernel for our new target, we pass the configuration file's name as `target` argument: To build our kernel for our new target, we pass the configuration file's name as `--target` argument. There is currently an [open bug][custom-target-bug] for custom target specifications, so you also need to set the `RUST_TARGET_PATH` environment variable to the current directory, otherwise Rust doesn't find your target. The full command is:
```bash [custom-target-bug]: https://github.com/rust-lang/cargo/issues/4905
cargo build --target=x86_64-blog_os
```
RUST_TARGET_PATH=$(pwd) cargo build --target x86_64-blog_os
``` ```
However, the following error occurs: However, the following error occurs:
@@ -228,7 +230,7 @@ Xargo is “a drop-in replacement for cargo”, so every cargo command also work
Let's try it: Let's try it:
```bash ```bash
> xargo build --target=x86_64-blog_os > RUST_TARGET_PATH=$(pwd) xargo build --target=x86_64-blog_os
Compiling core v0.0.0 (file:///…/rust/src/libcore) Compiling core v0.0.0 (file:///…/rust/src/libcore)
Finished release [optimized] target(s) in 22.87 secs Finished release [optimized] target(s) in 22.87 secs
Compiling blog_os v0.1.0 (file:///…/blog_os/tags) Compiling blog_os v0.1.0 (file:///…/blog_os/tags)
@@ -255,7 +257,7 @@ $(kernel): kernel $(rust_os) $(assembly_object_files) $(linker_script)
$(assembly_object_files) $(rust_os) $(assembly_object_files) $(rust_os)
kernel: kernel:
@xargo build --target $(target) @RUST_TARGET_PATH=$(pwd) xargo build --target $(target)
``` ```
We add a new `kernel` target that just executes `xargo build` and modify the `$(kernel)` target to link the created static lib. We also add the new `kernel` target to the `.PHONY` list, since it does not belong to a file with that name. We add a new `kernel` target that just executes `xargo build` and modify the `$(kernel)` target to link the created static lib. We also add the new `kernel` target to the `.PHONY` list, since it does not belong to a file with that name.