This is a simple GDB stub that can be easily dropped in to your project to allow you to debug a target platform using GDB (or another application which supports remote GDB targets). It has no library dependencies (such as libc) and requires just standard tools to build.
Communication between the stub and the debugger takes place via the GDB Remote Serial Protocol.
This was developed for x86 systems, but it's fairly modular. With a little
effort, it can be easily ported to other platforms. You will need to modify
gdbstub_sys.h and gdbstub_sys.c to fit your platform's needs accordingly.
Running make produces ELF binary gdbstub.elf with an entry point
(dbg_start) that will simply hook the current IDT (to support debug
interrupts) and break.
Additionally, a simple flat binary gdbstub.bin is created from the ELF binary.
The intent for this flat binary is to be trivially loaded and jumped to.
In demo/demo.c there is a simple function that's used for demonstration and
testing. To test the GDB stub out, you can launch an instance of the full-system
emulator QEMU as follows:
qemu-system-i386 -serial tcp:127.0.0.1:1234,server -display none -kernel gdbstub.elf
This will launch QEMU, create a virtual machine with a virtual serial port that can be connected to through local TCP port 1234, then load and run the stub executable inside the virtual machine.
You can then launch your local GDB client with the demo.gdbinit script to get
your GDB client to connect to the virtual serial port and begin debugging the
demo application:
gdb --command=demo/demo.gdbinit
For example, step a couple of times and print out the value of x:
(gdb) s 2
(gdb) p/x x
$1 = 0xdeadbeef
This software is published under the terms of the MIT License. See LICENSE.txt
for full license.
Matt Borgerson, 2016-2019