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Marc Koderer |
How to Contribute to the Linux Kernel |
|
Dev setup
Vagrant with your picked distro
Dont forget to resize you volume::
vagrant plugin install vagrant-disksize- Don't forget to increase CPU, MEM and disk
- Do not use shared FS for the kernel git
Vagrant.configure("2") do |config|
config.vm.box = "bento/ubuntu-20.04"
config.disksize.size = '100GB'
config.vm.provider "virtualbox" do |v|
v.memory = 4096
v.cpus = 4
v.name = "kernel"
end
end sudo apt-get update
sudo apt-get install -y libncurses-dev gawk flex bison bc
sudo apt-get install -y openssl libssl-dev dkms libelf-dev
sudo apt-get install -y libudev-dev libpci-dev libiberty-dev autoconf
sudo apt-get install -y git
# Optional
sudo apt install linux-headers-$(uname -r)Take a coffee
> git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> git clone git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
Cloning into 'linux'...
remote: Enumerating objects: 248, done.
remote: Counting objects: 100% (248/248), done.
remote: Compressing objects: 100% (148/148), done.
remote: Total 7990947 (delta 147), reused 140 (delta 100), pack-reused 7990699
Receiving objects: 100% (7990947/7990947), 2.12 GiB | 5.70 MiB/s, done.
Resolving deltas: 100% (6545813/6545813), done.
Updating files: 100% (71499/71499), done.
# copy current config (or make your own one with make menuconfig)
cp /boot/config-`uname -r`* .config
make -j4
make modules
sudo make modules_install
sudo make install
sudo update-grubStructure
┌─────────────────────────────────────────────────────────────────┐
│ Applications │
│ ┌────────────────────────────┐ │
└───────────────────────────┘System Libs (e.g. libc) └────────┘
│
┌───────────┐ ┌─────────────────────────▼─────────────────────────────────────┐
│ Modules │ │ ┌──────────────────────────────────────────────────────────┐ │
│ │ │ │ System Call Interface (SCI) │ │
│ │ │ │ │ │
│ │ │ └──────────────────────────────────────────────────────────┘ │
│ │ │ ┌───────────────────┐ ┌─────────────────┐ ┌─────────────┐ │
│ │ │ │ I/O │ │ Process │ │ Virt / Cont │ │
│ │ │ │ │ │ │ │ │ │
│ │ │ │ - File System │ │ - Scheduler │ │ - KVM │ │
│ │ │ │ - Networking │ │ - Mem Mgmt │ │ - Cgroups │ │
│ │ │ │ - Device Drivers │ │ - IPC │ │ - Net NS │ │
│ │ │ │ │ │ │ │ │ │
│ │ │ │ │ │ │ │ │ │
│ │ │ └───────────────────┘ └─────────────────┘ └─────────────┘ │
│ │ │ ┌──────────────────────────────────────────────────────────┐ │
│ │ │ │ │ │
│ │ │ │ Arch dependent Code │ │
│ │ │ │ │ │
│ │ │ └──────────────────────────────────────────────────────────┘ │
└───────────┘ └───────────────────────────────────────────────────────────────┘
┌─────────────────────────────────────────────────────────────────────────────┐
│ Hardware │
└─────────────────────────────────────────────────────────────────────────────┘
- Release Candidate (RC): Mainline pre-releases used for testing and feature development. An RC a two weeks cycle.
- Mainline: After muliple RC cycles a new mainline Kernel will be declared by Linus (2-3 months cycle)
- Stable: Only bug fixes allowed and those will be backproted from mainline
- Longterm (LTR): Longterm maintenance Kernels only with imporant bug fixes/backports
- Makefile This file is the top-level Makefile for the whole source tree
- MAINTAINERS Defines maintainers for each subsystem and area
- Documentation/ This directory contains a lot of useful information about configuring the kernel
- arch/: All the architecture specific code is in this directory
- crypto/ This is a cryptographic API for use by the kernel itself.
- drivers/ As a general rule, code to run peripheral devices is found in subdirectories of this directory.
- fs/ Both the generic filesystem code (VFS) and the code for each different filesystem
- include/: Most of the header files included at the beginning of a .c file
- ipc/: "IPC" stands for "Inter-Process Communication".
- kernel/: Generic kernel level code that doesn't fit anywhere else goes in here.
- lib/: Routines of generic usefulness to all kernel code are put in here.
- net/: The high-level networking code is here.
- scripts/: This directory contains scripts that are useful in building the kernel
- security/: Code for different Linux security models can be found here
- usr/: This directory contains code that builds a cpio-format
Source: https://courses.linuxchix.org/kernel-hacking-2002/08-overview-kernel-source.html
Let's get started
- Create a branch
git chechout -b my_feature - Do the change
- Commit it
git add ..andgit commit -s - git format-patch -1
- Check the patch scripts/checkpatch.pl my.patch
- Find the right DL/maintainer with
scripts/get_maintainer.pl - Send out the contribution
git send-email
Compile linux/samples/kprobes load the modules and have a look:
make -C ~/kernel/linux/ M=$PWD modules
sudo insmod kprobe_example.ko
sudo dmesg | tail
[ 911.102788] <kernel_clone> post_handler: p->addr = 0x00000000cdf2e666, flags = 0x206
[ 913.116030] <kernel_clone> pre_handler: p->addr = 0x00000000cdf2e666, ip = ffffffffad87d011, flags = 0x206
..Unload the kernel module
sudo rmmod kprobe_example.ko
sudo dmesg | tail -1
[ 919.433074] kprobe at 00000000cdf2e666 unregisteredIn kprobe_example.c the probed entry was changed from _do_fork to kernel_clone.
This could cause issues when executing the sample in older kernels (kernel_clone was introduced quite recently).
Let's change the code and probe a function that doesn't exist
diff --git a/samples/kprobes/kprobe_example.c b/samples/kprobes/kprobe_example.c
index 331dcf151532..794527f11667 100644
--- a/samples/kprobes/kprobe_example.c
+++ b/samples/kprobes/kprobe_example.c
@@ -15,7 +15,7 @@
#include <linux/kprobes.h>
#define MAX_SYMBOL_LEN 64
-static char symbol[MAX_SYMBOL_LEN] = "kernel_clone";
+static char symbol[MAX_SYMBOL_LEN] = "kernel_clone2";
module_param_string(symbol, symbol, sizeof(symbol), 0644);
/* For each probe you need to allocate a kprobe structure */Build it and load it
make -C ~/kernel/linux/ M=$PWD modules
sudo insmod kprobe_example.ko
insmod: ERROR: could not insert module kprobe_example.ko: Unknown symbol in module
sudo dmesg | tail -1
[ 2143.150210] register_kprobe failed, returned -2The -2 means ENOENT No such file or directory code. Let's add a more obvious error message.
diff --git a/samples/kprobes/kprobe_example.c b/samples/kprobes/kprobe_example.c
index 331dcf151532..a85304890374 100644
-- a/samples/kprobes/kprobe_example.c
++ b/samples/kprobes/kprobe_example.c
@@ -108,7 +108,12 @@ static int __init kprobe_init(void)
kp.fault_handler = handler_fault;
ret = register_kprobe(&kp);
- if (ret < 0) {
+ if (ret == -ENOENT){
+ /* Check in /proc/kallsyms for a valid symbol. */
+ pr_err("register_kprobe failed, symbol not found: %d\n", ret);
+ return ret;
+ }
+ else if (ret < 0) {
pr_err("register_kprobe failed, returned %d\n", ret);
return ret;
}- Let's extract a patch file
git checkout kprobe_err_msg
git format-patch -1- Check the patch
scripts/checkpatch.pl 0001-samples-kprobes-Adapt-error-handling.patch- Get the maintainers for the patch
scripts/get_maintainer.pl --no-rolestats 0001-samples-kprobes-Adapt-error-handling.patch ┌───────────────────────┐ ┌───────────────────────┐
│ mainline Kernel │ │ -next │
│ │ │ │
│ Linus Torvalds │ │ Stephen Rothwell │
│ │ │ │
└───────────────────────▲ └───────────────────▲───┘
▲ ▲ └───────────────────────┤
│ │ │
┌────────────────┴──────┐ ┌──┴────────────────────┐ ┌────┴──────────────────┐
│ sub system │ │ sub system │ │ sub system │
│ │ │ │ │ │
│ Maintainer / ML │ │ Maintainer / ML │ │ Maintainer / ML │
│ │ │ │ │ │
└──────▲────────────────┘ └───────▲───────────────┘ └───────▲───────────────┘
│ │ │
│ │ │
┌─────┴────┐ ┌────┴─────┐ ┌────┴─────┐
│Developer │ │Developer │ │Developer │
└──────────┘ └──────────┘ └──────────┘
- https://lkml.org/lkml/2019/8/6/510
- https://lkml.org/lkml/2019/8/7/772
- https://lore.kernel.org/patchwork/patch/1128028/
- https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=3ee8d6c592dc7fb240574b84e9f9a7f9db4d4b42
sudo apt-get install git-email- content-type text/plain
- No HTML mails!
- No signatures
- No attachments
- Patches with git format-patch
- Patches with
git commit -s
[sendemail]
; setup for using git send-email; prompts for password
smtpuser = [email protected]
smtpserver = SMTPSERVER
smtpencryption = tls
smtpserverport = 587
[user]
email = [email protected]
name = Marc Koderer