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README.md

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+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.
+
+## 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`](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 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).