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Update “Set Up Rust” post to use the cargo panic option

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Philipp Oppermann
2016-05-29 18:35:16 +02:00
parent f4eb589f19
commit d7b05bc6b4
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blog/post/2015-09-02-set-up-rust.md
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@@ -219,17 +219,31 @@ target/debug/libblog_os.a(blog_os.0.o):
/home/.../src/libcore/iter.rs:654: /home/.../src/libcore/iter.rs:654:
undefined reference to `_Unwind_Resume' undefined reference to `_Unwind_Resume'
``` ```
So the linker can't find a function named `_Unwind_Resume` that is referenced in `iter.rs:654` in libcore. This reference is not really there at [line 654 of libcore's `iter.rs`][iter.rs:654]. Instead, it is a compiler inserted _landing pad_, which is used for exception handling. So the linker can't find a function named `_Unwind_Resume` that is referenced in `iter.rs:654` in libcore. This reference is not really there at [line 654 of libcore's `iter.rs`][iter.rs:654]. Instead, it is a compiler inserted _landing pad_, which is used for panic handling by default.
[iter.rs:654]: https://github.com/rust-lang/rust/blob/b0ca03923359afc8df92a802b7cc1476a72fb2d0/src/libcore/iter.rs#L654 [iter.rs:654]: https://github.com/rust-lang/rust/blob/b0ca03923359afc8df92a802b7cc1476a72fb2d0/src/libcore/iter.rs#L654
The easiest way of fixing this problem is to disable the landing pad creation since we don't supports panics anyway right now. We can do this by passing a `-Z no-landing-pads` flag to `rustc` (the actual Rust compiler below cargo). To do this we replace the `cargo build` command in our Makefile with the `cargo rustc` command, which does the same but allows passing flags to `rustc`: By default, the destructors of all stack variables are run when a `panic` occurs. This is called _unwinding_ and allows parent threads to [recover from panics]. However, it requires a platform specific gcc library, which isn't available in our kernel.
```make [recover from panics]: https://doc.rust-lang.org/book/concurrency.html#panics
cargo:
@cargo rustc --target $(target) -- -Z no-landing-pads Fortunately, Rust allows us to disable unwinding. We just need to add some entries in our `Cargo.toml`:
```toml
# The development profile, used for `cargo build`.
[profile.dev]
panic = "abort"
# The release profile, used for `cargo build --release`.
[profile.release]
panic = "abort"
``` ```
Now we fixed all linking issues and our kernel should _build_ again. But instead of displaying `Hello World`, it constantly reboots itself when we start it.
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.
[profile sections]: http://doc.crates.io/manifest.html#the-profile-sections
Now we fixed all linking issues and our kernel builds again. But instead of displaying `Hello World`, it constantly reboots itself when we start it.
## Debugging the Boot Loop ## Debugging the Boot Loop
Such a boot loop is most likely caused by some [CPU exception][exception table]. When these exceptions aren't handled, a [Triple Fault] occurs and the processor resets itself. We can look at generated CPU interrupts/exceptions using QEMU: Such a boot loop is most likely caused by some [CPU exception][exception table]. When these exceptions aren't handled, a [Triple Fault] occurs and the processor resets itself. We can look at generated CPU interrupts/exceptions using QEMU: