How can I debug QEMU with one terminal?

Question

I am working on a moon rover for Carnegie Mellon University which will be launching next year. Specifically, I am working on a flight computer called the ISIS OBC (On Board Computer) and I am trying to find out how to first run QEMU in a terminal in the background, and then run GDB to connect to the QEMU instance I just backgrounded. I have tried running QEMU in the background with & as well as using the flag -daemonize but this causes QEMU's GDB server to not work at all.

The overarching goal is to be able to debug our flight software in GDB in one terminal window so that I can run it from inside a Docker container mounted on the repository's root. It takes a bit of setup to get be able to debug our code, with a couple of gotchas like incompatibility with newer versions of GCC, so being able to run the CODE and debug it from inside a Docker container (which has all our other development dependencies installed too) is a must.

My current solution was to just run QEMU in another gnome-terminal I initialized in the startup script completely outside of the docker container, but this will not work in Docker for obvious reasons. Here is that code in case the additional context is helpful:

#!/bin/bash
#The goal of the below code is to get the stdout from QEMU piped into GDB. 
#Unfourtunately it appears that QEMU must be started as the FG in its own window so that it will 
#start its GDB server, so an additional window is required. 

my_tty=$(tty)
gnome-terminal -- bash -c './../obc-emulation-resources/obc-qemu/iobc-loader -f sdram build/app.isis-obc-rtos.bin -s sdram -o pmc-mclk -- -serial stdio -monitor none -s -S > /tmp/qemu-gdb; $SHELL' --name="QEMU-iOBC" --title="QEMU-iOBC" -p
tail -f /tmp/qemu-gdb > $my_tty&
./third_party/gcc-arm-none-eabi-10.3-2021.07/bin/arm-none-eabi-gdb     -ex='target remote localhost:1234'     -ex='symbol-file build/isis-obc-rtos.elf' 

# Kill any leftover qemu debugging sessions
kill $(ps aux | grep '[i]obc-loader' | awk '{print $2}')

# Delete intermediate file
rm -f /tmp/qemu-gdb

# Get's rid of any extra text that may occur
echo ""
clear

I would much prefer to run something like this to achieve my goal:

./../obc-emulation-resources/obc-qemu/iobc-loader -f sdram build/app.isis-obc-rtos.bin -s sdram -o pmc-mclk -- -serial stdio -monitor none -s -S > /tmp/qemu-gdb

rather than what I am running now:

gnome-terminal -- bash -c './../obc-emulation-resources/obc-qemu/iobc-loader -f sdram build/app.isis-obc-rtos.bin -s sdram -o pmc-mclk -- -serial stdio -monitor none -s -S > /tmp/qemu-gdb; $SHELL' --name="QEMU-iOBC" --title="QEMU-iOBC" -p

"iobc-loader" is a wrapper used to run the QEMU command by the way."app.isis-obc-rtos.bin" is of course the binary I am trying to run and "isis-obc-rtos.elf" contains the symbols used to debug it. Apologies if the answer is obvious, I am a student!

Answer 1

You can try using a terminal multiplexer like screen or tmux , which allow you to run each command in foreground in a separate virtual terminal.

You can also create panes, for example with tmux press Ctrl+b " to split the screen horizontally or Ctrl+b % to split it vertically, then Ctrl+bo to cycle between them.

Answer 2

Using tmux is definitely the easiest approach, especially with its built in CLI support. You could write a script similar to this one:

tmux start-server
tmux new-session -d -s debug-session -n isis -d "<cmd1>";"<cmd2>"

Where cmd1 is your QEMU execution script, and cmd2 is another script that runs the docker you want to use for debugging.