debugging linux with dynamic debugging and dmesg
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@ -17,11 +17,11 @@ qemu-img create disk.img 15G
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{% endhighlight %}
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- Start the machine and [install Archlinux](https://wiki.archlinux.org/title/Installation_guide)
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{% highlight bash %}
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qemu-system-x86_64 -cdrom archlinux-2021.11.01-x86_64.iso -boot order=d -drive format=raw,file=disk.img -m 8G -smp cpus=4
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qemu-system-x86_64 -cdrom archlinux-2021.11.01-x86_64.iso -boot order=d -drive format=raw,file=disk.img -m 8G
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{% endhighlight %}
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- Start the machine after installing
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- Start the machine after installing (note I forward 2222 to 22 so I can SSH/SCP to the virtual machine. I also set 4 CPUs so I can use threads for faster builds in the VM)
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{% highlight bash %}
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qemu-system-x86_64 -drive format=raw,file=disk.img -m 2G
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qemu-system-x86_64 -boot -drive format=raw,file=disk.img -m 8G -smp cpus=4 -net user,hostfwd=tcp::2222-:22 -net nic
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{% endhighlight %}
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- Install dependencies:
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{% highlight bash %}
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@ -56,3 +56,33 @@ mkinitcpio -k $RELEASE -s autodetect -g /boot/initramfs-linux-fallback${RELEASE}
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grub-mkconfig -o /boot/grub/grub.cfg
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{% endhighlight %}
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- Reboot and choose the new kernel (might be under "Advanced" in the bootloader)
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- Setup your environment for development. Mine consists of setting up tmux so I can have multiple terminals and neovim.
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{% highlight bash %}
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pacman -S neovim openssh tmux
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echo '[[ -z "$TMUX" ]] && exec tmux' >> /etc/profile
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# also follow https://github.com/junegunn/vim-plug for Neovim
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{% endhighlight %}
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And in the host:
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{% highlight bash %}
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scp -P 2222 ~/.tmux.conf root@localhost:/root
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scp -r -P 2222 ~/.config/nvim root@localhost:/root/.config/
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{% endhighlight %}
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# Debugging Logs
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There is a `pr_debug` function used over the code, in order to enable those logs in `dmesg` for a specific module, you can do this:
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{% highlight bash %}
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echo 'module ip_set +p' > /sys/kernel/debug/dynamic_debug/control
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{% endhighlight %}
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Note that, this works if you have dynamic debug enabled in your `.config`:
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{% highlight bash %}
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CONFIG_DYNAMIC_DEBUG=y
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CONFIG_DYNAMIC_DEBUG_CORE=y
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{% endhighlight %}
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You can then look at `dmesg` while running the code to see those logs:
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{% highlight bash %}
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dmesg
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{% endhighlight %}
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