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npx skills add https://github.com/mohitmishra786/low-level-dev-skills --skill rust-debuggingBefore you start
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Original skill document
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Rust Debugging
Purpose
Guide agents through debugging Rust programs: GDB/LLDB with Rust pretty-printers, backtrace configuration, panic triage, async debugging with tokio-console, and #[no_std] debugging strategies.
Triggers
- "How do I use GDB/LLDB to debug a Rust binary?"
- "How do I get a full backtrace from a Rust panic?"
- "How do I debug async Rust / Tokio?"
- "Rust pretty-printers aren't working in GDB"
- "How do I debug a Rust panic in production?"
- "How do I use dbg! and tracing in Rust?"
Workflow
1. Build for debugging
bash
# Debug build (default) — full debug info, no optimization
cargo build
# Release with debug info (for profiling real workloads)
cargo build --release --profile release-with-debug
# Or configure in Cargo.toml:
# [profile.release-with-debug]
# inherits = "release"
# debug = true
# Run directly
cargo run
cargo run -- arg1 arg22. GDB with Rust pretty-printers
bash
# Use rust-gdb wrapper (sets up pretty-printers automatically)
rust-gdb target/debug/myapp
# Or set up manually in ~/.gdbinit:
# python
# import subprocess, sys
# ...Common GDB session for Rust:
gdb
# Basic
(gdb) break main
(gdb) run arg1 arg2
(gdb) next # step over
(gdb) step # step into
(gdb) continue
# Rust-aware inspection
(gdb) print my_string # Shows String content via pretty-printer
(gdb) print my_vec # Shows Vec elements
(gdb) print my_option # Shows Some(value) or None
(gdb) info locals
# Break on panic
(gdb) break rust_panic
(gdb) break core::panicking::panic
# Backtrace
(gdb) bt # Short backtrace
(gdb) bt full # Full with locals3. LLDB with Rust pretty-printers
bash
# Use rust-lldb wrapper
rust-lldb target/debug/myapp
# Manual setup
lldb target/debug/myapp
(lldb) command script import /path/to/rust/lib/rustlib/etc/lldb_lookup.py
(lldb) command source /path/to/rust/lib/rustlib/etc/lldb_commandsCommon LLDB session:
lldb
(lldb) b main::main
(lldb) r arg1 arg2
(lldb) n # next (step over)
(lldb) s # step into
(lldb) c # continue
(lldb) frame variable # show locals
(lldb) p my_string # print variable with pretty-printer
(lldb) bt # backtrace
(lldb) bt all # all threads4. Backtrace configuration
bash
# Short backtrace (default on panic)
RUST_BACKTRACE=1 ./myapp
# Full backtrace with all frames
RUST_BACKTRACE=full ./myapp
# With symbols (requires debug build or separate debug info)
RUST_BACKTRACE=full ./target/debug/myapp
# Capture backtrace programmatically
use std::backtrace::Backtrace;
let bt = Backtrace::capture();
eprintln!("{bt}");For release binaries, keep debug symbols in a separate file:
bash
# Build release with debug info
cargo build --release
objcopy --only-keep-debug target/release/myapp target/release/myapp.debug
strip --strip-debug target/release/myapp
objcopy --add-gnu-debuglink=target/release/myapp.debug target/release/myapp5. Panic triage
rust
// Set a custom panic hook for structured logging
use std::panic;
panic::set_hook(Box::new(|info| {
let backtrace = std::backtrace::Backtrace::force_capture();
eprintln!("PANIC: {info}");
eprintln!("{backtrace}");
// Log to file, send to Sentry, etc.
}));Common panic patterns:
| Panic message | Likely cause |
|---|---|
index out of bounds: the len is N but the index is M | Array/vec OOB access |
called Option::unwrap() on a None value | Unwrap on None |
called Result::unwrap() on an Err value | Unwrap on error |
attempt to subtract with overflow | Integer underflow (debug build) |
assertion failed | Failed assert! or assert_eq! |
stack overflow | Infinite recursion |
Use panic = "abort" in release to get a crash dump instead of unwind.
6. The dbg! macro
rust
// dbg! prints file, line, value and returns the value
let result = dbg!(some_computation(x));
// prints: [src/main.rs:15] some_computation(x) = 42
// Chain multiple values
let (a, b) = dbg!((compute_a(), compute_b()));
// Inspect inside iterator chains
let sum: i32 = (0..10)
.filter(|x| dbg!(x % 2 == 0))
.map(|x| dbg!(x * x))
.sum();7. Structured logging with tracing
toml
[dependencies]
tracing = "0.1"
tracing-subscriber = { version = "0.3", features = ["env-filter"] }rust
use tracing::{debug, error, info, instrument, warn};
#[instrument] // Auto-traces function entry/exit with arguments
fn process(id: u64, data: &str) -> Result<(), Error> {
debug!("Processing item");
info!(item_id = id, "Started processing");
if data.is_empty() {
warn!(item_id = id, "Empty data");
return Err(Error::EmptyData);
}
error!(item_id = id, err = ?some_result, "Failed");
Ok(())
}
// Initialize in main
tracing_subscriber::fmt()
.with_env_filter("myapp=debug,warn")
.init();bash
# Control log levels at runtime
RUST_LOG=debug ./myapp
RUST_LOG=myapp::module=trace,warn ./myapp8. Async debugging with tokio-console
toml
[dependencies]
console-subscriber = "0.3"
tokio = { version = "1", features = ["full", "tracing"] }rust
// In main
console_subscriber::init();bash
# Install and run tokio-console
cargo install tokio-console
tokio-console # Connects to running Rust process at port 6669tokio-console shows: task states, waker activity, blocked tasks, poll durations.
For GDB/LLDB command reference and pretty-printer setup, see references/rust-gdb-pretty-printers.md.
Related skills
- Use
skills/rust/rustc-basicsfor debug info flags and build configuration - Use
skills/debuggers/gdbfor GDB fundamentals - Use
skills/debuggers/lldbfor LLDB fundamentals - Use
skills/rust/rust-sanitizers-mirifor memory safety and undefined behaviour
