When debugging Qemu, it might be helpoful to instrument Linux Kernel to see when interrupts get received, or see data on the other side of a transfer. If you have to modify the Kernel on a regular basis, it can be faster to build it in place than to build a customer RPM/DEB and install inside the VM. Here is how I have been going about updating the kernel.
Continue readingThe Qemu implementation uses a Flattened Device Tree (FTD) to manage the virtual implementation of the physical devices in a machine. I need to create a FTD entry for the MCTP-PCC implementation I am writing in Qemu. Since this is new to me, and I am working (as I most often do) via Ttrial and error, I want to see the FTD entry after I write it. Here is how I am dumping it.
Continue readingWhen developing Linux Kernel code, I have found myself wanting to have a test fixture inside the Firmware that lets me inspect the values communicated out of and into the Linux Kernel. I am currently writing one such fixture in Qemu. And I have an interrupt that is not getting handled by the Linux Kernel, I think because it is not getting delivered.
I have found it quite valuable to run this Qemu process in the Gnu Debugger. Here is how I (with help) got to the bottom of the mystery.
Continue readingMy defaults are set for Linux Kernel development, but I have been in Qemu land lately and these values make it easier to format.
set shiftwidth=4
set expandtab
set tabstop=4
retab
Using ebpf and the bpftrace command line utility, you can perform simple reporting on function calls. Here’s an example:
Continue readingI have an application that I want to share with my team. Fortunately, we have a shared server, so it is pretty easy to do so: if I put a file in /usr/local/bin it can A) be executed by anyone on the server and B) will not interfere with RPM packages. But, I do potentially want to put this code on other machines as well, so I am going to buld it as a pip package, upload it to a team repo (apache HTTPD instance on this machine) and then install it from pip as root.
Continue readingWhile it is tempting to use printk or pr_info when coding in order to trace function in the Linux kernel calls, it turns out that there os a; ready a utility to simplify that. Here are the steps I used to enable ftrace for mcpt-pcc and figuring out where a function call stack ended (in the middle of a debugging session where I had broken it)
Continue readingThe following command will print a stack trace whenever pcc_send_data is called.
sudo bpftrace -e 'f:pcc_send_data{print(kstack())}'I have wasted a lot of time as a developer waiting for long running processes to complete. Whether it is a Linux Kernel compile, and Ansible Playbook tearing down and recreating a system on a remote server, or a gitlab pipeline building and testing code, the common problem is that my head is in the problem being addressed there, but I cannot do anything to verify hypotheses until the process completes. I often get distracted while waiting, and find that what could have been a 5 minute turn around has become a 2 hour turn around.
Continue readingApache provides a pretty standard screen to display directoyr contents if you do not provide any mods. We post artifacts up to a local server that I later need to download. Here are my hacky notes using command line utilities. I probably will convert this to python next.
Continue reading