unwinding/README.md

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
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 crate provided, and use LD_PRELOAD to replace the system unwinder with it.

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

extern crate unwind;

Personality and other utilities

The library also provides Rust personality function. 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/.

TODO

• A better project name!
• Remove dependencies on alloc.