1/14/2024 0 Comments Grep command linux kernel![]() Now we can reference the struct in our bpftrace code! Structs defined in a. #include kprobe:do_filp_open /comm = str ( $1 )/ Here’s a common query I use to find a system call implementation: Once you have your ctag database generated, you can ctrl-click your way through the code to explore code paths. Go to the release page or the Linux GitHub page to download a release zip or tarball. You can run git clone too, but Linux has so many commits that it will take a long time and fill up a huge amount of hard drive space, so I strongly recommend that you download a release tarball of the source. Then you’ll want to download the release tarball for the version of Linux that shows up. Next, you need to figure out what version of the kernel you’re on. A ctags plugin, which reads a ctag database file and allows you to ctrl-click into code.File-search and open, this is available in VSCode by hitting ctrl-p, and in vim by using fzf.vim.ctags and a text editorīefore you get started with this method, you’ll want to make sure you’re in an editor which has the following functionality: Lxr has better code navigation and kernel version support than Livegrep, so I usually use both of them together. Livegrep has a web interface where you can search against paths, specific file types (*.c, *.h), and use regular expressions in your search. Livegrep and lxr are useful for quick searches. I have three methods that I like to use to search the Linux source: livegrep, lxr, and ctags. Generally, if you’re trying to look for data that is coming in (network, keyboard, etc.) from I/O, this will be somewhere in the bottom half. The bottom half picks up the work and does any processing required, such as notifying your web browser that a response came back from a server, or notifying your terminal program that a key was typed. The top half’s responsibility is to immediately handle the interrupt and schedule some work later to take care of it. ![]() ![]() ![]() A network card has some data ready to be read.The top half responds to “interrupts” which come to the CPU from some device or timer. The Linux kernel is split into two halves. Interrupts, top half, and bottom half work Here is a link to see all of the system calls for the x86_64 architecture. You can also find them listed in the system call table. These are defined with a macro called SYSCALL_DEFINE3 which generally takes the form, SYSCALL_DEFINE3(syscall_name, args.). When looking to see what’s going on on Linux, the first place you can start is with system calls. System calls have names, such as read() for reading a file that we can call directly in our code. The API of the Linux kernel is available through system calls. They call into the Linux kernel using provided APIs to get access to resources. The programs we run on Linux, like web browsers and text editors, are the clients. I like to think of the Linux kernel as a kind of server which provides APIs for things like access to the CPU, network data, keyboard keystrokes, mouse movements, files on the hard drive, and lots of other things. I’ll be going briefly into the two things that I think are fundamental to understanding how the Linux kernel work: system calls and interrupt handling. Understanding the Linux Kernel is a good book which goes into lots of details about Linux.The Linux Programming Interface is a wonderful book about the interface that programs use to talk to Linux.the docs can have some good information.linux-insides is a free Git book which has lots of details about Linux internals.If you’re curious and want to learn more, I recommend diving a bit deeper using a few of the following books and websites (note: I don’t use affiliate links or anything): Understanding the basic kernel architecture The three things that helped me get over this feeling were having a basic understanding of the Linux kernel architecture, having some tools to search the Linux kernel code, and knowing how to trace my programs in real time to see which code is getting called and when. I’ve felt a bit intimidated in the past by opening up the Linux source tree and reading through the code. answering questions like: Where in the Linux kernel is my code calling into and spending the most time? Debugging an issue which may be caused by a kernel bug, or strange kernel behavior.what happens when you make an open() system call Here are a few of reasons I’ve chosen to read the Linux source:
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