Rust Debugging Skill

This skill provides commands and workflows for inspecting binaries and debugging the OS components on Linux.

Prerequisites

• •LLVM Tools: Ensure llvm-tools-preview is installed:
  bash

  rustup component add llvm-tools-preview
  

• •Rust Object Tools: Recommended usage via rust-objdump, rust-nm, or standard llvm-* tools found in your Rust toolchain.
• •GDB: Ensure gdb or rust-gdb is installed (sudo apt install gdb).

1. User Space Debugging (Static Musl Binaries)

For user space programs compiled with x86_64-unknown-linux-musl and crt-static.

List Symbols (nm)

To see all symbols in a binary (with Rust demangling):

rust-nm <BINARY>
# Or using standard nm (demangle with rustfilt if installed)
nm <BINARY> | rustfilt

Disassemble (objdump)

To view the assembly instructions. rust-objdump automatically demangles names:

rust-objdump -d <BINARY>

Look for _start or main to verify the entry point.

Check ELF Headers (readobj)

To verify if it's a valid statically linked ELF:

rust-readobj -h <BINARY>

2. Kernel & Bootloader Debugging

Inspect Initial RAM Disk / UEFI Payload

Use llvm-objdump to check the kernel binary structure before it gets packed.

rust-objdump -h target/x86_64-unknown-none/release/kernel

QEMU + GDB Debugging

To debug the running kernel with GDB:

1. •

   Launch QEMU with GDB Stub: Add -s -S to your QEMU command.

   • •-s: Shorthand for -gdb tcp::1234
   • •-S: Freeze CPU at startup (wait for debugger)
2. •

   Attach GDB: Open a new terminal and run:

   bash

   rust-gdb target/x86_64-unknown-none/debug/kernel
   

   (Ensure you point to the compiled kernel binary to load symbols)

3. •

   Connect to QEMU: Inside GDB:

   gdb

   target remote :1234
   break _start
   continue
   

QEMU Monitor

When QEMU is running:

• •Press Ctrl+Alt+2 to switch to the QEMU Monitor.
• •Type info registers to see CPU state.
• •Type info mem to see memory mappings (if supported).
• •Press Ctrl+Alt+1 to return to the display.

3. Common Cargo Commands

• •Check Code: cargo check
• •Clippy: cargo clippy
• •Macro Expansion: cargo expand (requires cargo-expand crate)