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daniel5151 / gdbstub

An ergonomic, featureful, and easy-to-integrate implementation of the GDB Remote Serial Protocol in Rust (with no-compromises #![no_std] support)
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debugger debugging embedded emulation emulators gdb gdb-protocol gdb-rsp gdbstub no-std packet packet-parsing rsp rust

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gdbstub

An ergonomic, featureful, and easy-to-integrate implementation of the GDB Remote Serial Protocol in Rust, with no-compromises #![no_std] support.

gdbstub makes it easy to integrate powerful guest debugging support to your emulator / hypervisor / debugger / embedded project. By implementing just a few basic methods of the gdbstub::Target trait, you can have a rich GDB debugging session up and running in no time!

gdbstub's API makes extensive use of a technique called Inlineable Dyn Extension Traits (IDETs) to expose fine-grained, zero-cost control over enabled GDB protocol features without relying on compile-time features flags. Aside from making it effortless to toggle enabled protocol features, IDETs also ensure that any unimplemented features are guaranteed to be dead-code-eliminated in release builds!

If you're looking for a quick snippet of example code to see what a featureful gdbstub integration might look like, check out examples/armv4t/gdb/mod.rs

Why use gdbstub?

Can I Use gdbstub in Production?

Yes, as long as you don't mind some API churn until 1.0.0 is released.

Due to gdbstub's heavy use of Rust's type system in enforcing GDB protocol invariants at compile time, it's often been the case that implementing new GDB protocol features has required making some breaking API changes. While these changes are typically quite minor, they are nonetheless semver-breaking, and may require a code-change when moving between versions. Any particularly involved changes will typically be documented in a dedicated transition guide document.

That being said, gdbstub has already been integrated into many real-world projects since its initial 0.1 release, and empirical evidence suggests that it seems to be doing its job quite well! Thusfar, most reported issues have been caused by improperly implemented Target and/or Arch implementations, while the core gdbstub library itself has proven to be reasonably bug-free.

See the Future Plans + Roadmap to 1.0.0 for more information on what features gdbstub still needs to implement before committing to API stability with version 1.0.0.

Debugging Features

The GDB Remote Serial Protocol is surprisingly complex, supporting advanced features such as remote file I/O, spawning new processes, "rewinding" program execution, and much, much more. Thankfully, most of these features are completely optional, and getting a basic debugging session up-and-running only requires implementing a few basic methods:

Yep, that's right! That's all it takes to get gdb connected!

Of course, most use-cases will want to support additional debugging features as well. At the moment, gdbstub implements the following GDB protocol extensions:

Note: GDB features are implemented on an as-needed basis by gdbstub's contributors. If there's a missing GDB feature that you'd like gdbstub to implement, please file an issue and/or open a PR!

For a full list of GDB remote features, check out the GDB Remote Configuration Docs for a table of GDB commands + their corresponding Remote Serial Protocol packets.

Zero-overhead Protocol Extensions

Using a technique called Inlineable Dyn Extension Traits (IDETs), gdbstub is able to leverage the Rust compiler's powerful optimization passes to ensure any unused features are dead-code-eliminated in release builds without having to rely on compile-time features flags!

For example, if your target doesn't implement a custom GDB monitor command handler, the resulting binary won't include any code related to parsing / handling the underlying qRcmd packet!

If you're interested in the low-level technical details of how IDETs work, I've included a brief writeup in the documentation here.

Feature flags

By default, the std and alloc features are enabled.

When using gdbstub in #![no_std] contexts, make sure to set default-features = false.

Examples

Real-World Examples

While some of these projects may use older versions of gdbstub, they can nonetheless serve as useful examples of what a typical gdbstub integration might look like.

If you end up using gdbstub in your project, consider opening a PR and adding it to this list!

In-tree "Toy" Examples

These examples are built as part of the CI, and are guaranteed to be kept up to date with the latest version of gdbstub's API.

unsafe in gdbstub

gdbstub limits its use of unsafe to a bare minimum, with all uses of unsafe required to have a corresponding // SAFETY comment as justification.

For those paranoid about trusting third-party unsafe code, gdbstub comes with an opt-in paranoid_unsafe feature, which enables #![forbid(unsafe_code)] on the entire gdbstub crate, swapping out all instances of unsafe code with equivalent (albeit less-performant) alternatives.

The following list exhaustively documents all uses of unsafe in gdbstub:

Writing panic-free code

Ideally, the Rust compiler would have some way to opt-in to a strict "no-panic" mode. Unfortunately, at the time of writing (2022/04/24), no such mode exists. As such, the only way to avoid the Rust compiler + stdlib's implicit panics is by being very careful when writing code, and manually checking that those panicking paths get optimized out!

And when I say "manually checking", I mean checking generated asm output.

Why even go through this effort?

As such, gdbstub promises to introduce zero additional panics into an existing project, subject to the following conditions:

  1. The binary is compiled in release mode
    • *subject to the specific rustc version being used (codegen and optimization vary between versions)
    • *different hardware architectures may be subject to different compiler optimizations
      • i.e: at this time, only x86 is actively tested to be panic-free
  2. gdbstub's paranoid_unsafe cargo feature is disabled
    • LLVM is unable to omit certain panic checks without requiring a bit of unsafe code
    • See the unsafe in gdbstub section for more details
  3. The Arch implementation being used doesn't include panicking code
    • Note: The arch implementations under gdbstub_arch are not guaranteed to be panic free!
    • If you do spot a panicking arch in gdbstub_arch, consider opening a PR to fix it

If you're using gdbstub in a no-panic project and have determined that gdbstub is at fault for introducing a panicking code path, please file an issue!

Future Plans + Roadmap to 1.0.0

While the vast majority of GDB protocol features (e.g: remote filesystem support, tracepoint packets, most query packets, etc...) should not require breaking API changes, the following features will most likely require at least some breaking API changes, and should therefore be implemented prior to 1.0.0.

Not that this is not an exhaustive list, and is subject to change.

Additionally, while not strict blockers to 1.0.0, it would be good to explore these features as well:

License

gdbstub is free and open source! All code in this repository is dual-licensed under either:

at your option. This means you can select the license you prefer! This dual-licensing approach is the de-facto standard in the Rust ecosystem and there are very good reasons to include both.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.