70 lines
3.7 KiB
Markdown
70 lines
3.7 KiB
Markdown
Unwinding library in Rust and for Rust
|
|
======================================
|
|
|
|
This library serves two purposes:
|
|
1. Provide a pure Rust alternative to libgcc_eh or libunwind.
|
|
2. Provide easier unwinding support for `#![no_std]` targets.
|
|
|
|
Currently supports x86_64 and RV64.
|
|
|
|
## Unwinder
|
|
|
|
The unwinder can be enabled with `unwinder` feature. Here are the feature gates related to
|
|
the unwinder:
|
|
| Feature | Default | Description |
|
|
|--------------|---------|-|
|
|
| unwinder | Yes | The primary feature gate to enable the unwinder |
|
|
| fde-phdr | Yes | Use `dl_iterator_phdr` to retrieve frame unwind table. Depends on libc. |
|
|
| fde-registry | Yes | Provide `__register__frame` and others for dynamic registration |
|
|
| fde-static | No | Use `__executable_start`, `__etext` and `__eh_frame` to retrieve frame unwind table. The former two symbols are usually provided by the linker, while the last one would need to be provided by the user via linker script. |
|
|
| dwarf-expr | Yes | Enable the dwarf expression evaluator. Usually not necessary for Rust |
|
|
| hide-trace | Yes | Hide unwinder frames in back trace |
|
|
|
|
If you want to use the unwinder for other Rust (C++, or any programs that utilize the unwinder), you can build the [`unwind_dyn`](cdylib) crate provided, and use `LD_PRELOAD` to replace the system unwinder with it.
|
|
```sh
|
|
cd cdylib
|
|
cargo build --release
|
|
# Test the unwinder using rustc. Why not :)
|
|
LD_PRELOAD=`../target/release/libunwind_dyn.so` rustc +nightly -Ztreat-err-as-bug
|
|
```
|
|
|
|
If you want to link to the unwinder in a Rust binary, simply add
|
|
```rust
|
|
extern crate unwind;
|
|
```
|
|
|
|
## Personality and other utilities
|
|
|
|
The library also provides Rust personality function. This can work with the unwinder described above or with a different unwinder. This can be handy if you are working on a `#![no_std]` binary/staticlib/cdylib and you still want unwinding support.
|
|
|
|
Here are the feature gates related:
|
|
| Feature | Default | Description |
|
|
|---------------|---------|-|
|
|
| personality | No | Provides `#[lang = eh_personality]` |
|
|
| print | No | Provides `(e)?print(ln)?`. This is really only here because panic handler needs to provide things. Depends on libc. |
|
|
| panic | No | Provides `begin_panic` and `catch_unwind`. Only stack unwinding functionality is provided and no printing is done, because this feature does not depend on libc. |
|
|
| panic-handler | No | Provides `#[panic_handler]`. Provides similar behaviour on panic to std, with `RUST_BACKTRACE` support as well. Stack trace won't have symbols though. Depends on libc. |
|
|
| system-alloc | No | Provides a global allocator which calls `malloc` and friends. Provided for convience. |
|
|
|
|
If you are writing a `#![no_std]` program, simply enable `personality`, `panic-handler` and `system-alloc` in addition to the defaults, you instantly obtains the ability to do unwinding! An example is given in [`example/`](example).
|
|
|
|
## Baremetal
|
|
|
|
To use this library for baremetal projects, disable default features and enable `unwinder`, `fde-static`, `personality`, `panic`. `dwarf-expr` and `hide-trace` are optional. Modify the linker script by
|
|
```ld
|
|
/* Inserting these two lines */
|
|
. = ALIGN(8);
|
|
PROVIDE(__eh_frame = .);
|
|
/* before .eh_frame rule */
|
|
.eh_frame : { KEEP (*(.eh_frame)) *(.eh_frame.*) }
|
|
```
|
|
|
|
And that's it! After you ensured that the global allocator is functional, you can use `unwind::panic::begin_panic` to initiate an unwing and catch using `unwind::panic::catch_unwind`, as if you have a `std`.
|
|
|
|
If you have your own version of `thread_local` and `println!` working, you can port [`panic_handler.rs`](src/panic_handler.rs) for double-panic protection and stack traces!
|
|
|
|
## TODO
|
|
|
|
* A better project name!
|
|
* Remove dependencies on `alloc`.
|