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Disable unwinding in the target config file

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Philipp Oppermann
2017-04-11 19:39:19 +02:00
parent 388f014fc3
commit f72cfbff34
3 changed files with 28 additions and 29 deletions
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9
Cargo.toml
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@@ -20,14 +20,5 @@ path = "libs/hole_list_allocator"
features = ["spin_no_std"] features = ["spin_no_std"]
version = "0.2.1" version = "0.2.1"
[lib] [lib]
crate-type = ["staticlib"] crate-type = ["staticlib"]
[profile]
[profile.dev]
panic = "abort"
[profile.release]
panic = "abort"

45
blog/content/post/03-set-up-rust.md
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@@ -395,34 +395,41 @@ By default, the destructors of all stack variables are run when a `panic` occurs
[recover from panics]: https://doc.rust-lang.org/book/concurrency.html#panics [recover from panics]: https://doc.rust-lang.org/book/concurrency.html#panics
Fortunately, Rust allows us to disable unwinding. We just need to add some entries in our `Cargo.toml`: Fortunately, Rust allows us to disable unwinding for our target. For that we add the following line to our `x86_64-blog_os.json` file:
```toml ```json
# The development profile, used for `cargo build`. {
[profile.dev] "...",
panic = "abort" "panic-strategy": "abort"
}
# The release profile, used for `cargo build --release`.
[profile.release]
panic = "abort"
``` ```
These [profile sections] specify options for `cargo build` and `cargo release`. By setting the `panic` option to `abort`, we disable all unwinding in our kernel. By setting the [panic strategy] to `abort` instead of the default `unwind`, we disable all unwinding in our kernel. Let's try `make run` again:
[profile sections]: http://doc.crates.io/manifest.html#the-profile-sections [panic strategy]: https://github.com/nox/rust-rfcs/blob/master/text/1513-less-unwinding.md
However, there are still references to `_Unwind_Resume` in the precompiled standard libraries. This might lead to linker errors when we use specific parts of `libcore`. To avoid this, we create a dummy `_Unwind_Resume` function that loops indefinitely[^fn-libcore-unwind]: ```
Compiling core v0.0.0 (file:///…/rust/src/libcore)
Finished release [optimized] target(s) in 22.24 secs
Finished dev [unoptimized + debuginfo] target(s) in 0.5 secs
target/x86_64-blog_os/debug/libblog_os.a(blog_os-b5a29f28b14f1f1f.0.o):
In function `core::ptr::drop_in_place<…>':
/…/src/libcore/ptr.rs:66:
undefined reference to `_Unwind_Resume'
...
```
[^fn-libcore-unwind]: A better solution is to recompile `libcore` with `panic="abort"`. We will do this in a future post. We see that `xargo` recompiles the `core` crate, but the `_Unwind_Resume` error still occurs. This is because our `blog_os` crate was not recompiled somehow and thus still references the unwinding function. To fix this, we need to force a recompile using `cargo clean`:
```rust ```
// in src/lib.rs > cargo clean
> make run
Compiling rlibc v1.0.0
Compiling blog_os v0.1.0 (file:///home/philipp/Documents/blog_os/tags)
warning: unused variable: `test` […]
#[allow(non_snake_case)] Finished dev [unoptimized + debuginfo] target(s) in 0.60 secs
#[no_mangle]
pub extern "C" fn _Unwind_Resume() -> ! {
loop {}
}
``` ```
It worked! We no longer see linker errors and our kernel prints `OKAY` again. It worked! We no longer see linker errors and our kernel prints `OKAY` again.

3
x86_64-blog_os.json
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@@ -6,5 +6,6 @@
"arch": "x86_64", "arch": "x86_64",
"os": "none", "os": "none",
"features": "-mmx,-sse,+soft-float", "features": "-mmx,-sse,+soft-float",
"disable-redzone": true "disable-redzone": true,
"panic": "abort"
} }