Debug a Kernel Module with QEMU + GDB Remote

QEMU + GDB Remote Debugging

QEMU includes a built-in GDB stub that allows remote debugging of operating systems and kernel code without physical hardware. Kernel developers and security researchers use this workflow daily.

Setting Up Remote Debugging

Start QEMU with the GDB stub:

• -s: Shorthand for -gdb tcp::1234
• -S: Pause CPU at startup until GDB connects

Connect from GDB:

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Once connected, you can examine registers with info registers, step through boot code with stepi, and inspect memory at known addresses with x/10x 0x100000.

For This Exercise

You will document the QEMU + GDB remote debugging workflow for kernel development. This exercise asks you to explain how to set breakpoints in kernel code and load module symbols, skills you will need when analyzing OS behavior or developing kernel modules.

Kernel Module Symbols

After the guest boots, load a module with insmod and find its base address in /proc/modules. In GDB, use add-symbol-file module.ko 0xaddress to load debug symbols at the correct relocation. Without this step, breakpoints in module code miss because GDB only knows the kernel's main symbol table. QEMU's stub exposes the full guest register set as if you were debugging bare metal.