Update instructions

2023-10-29 19:51:36 +01:00 · 2023-10-29 19:51:36 +01:00 · 1fb8a54b4b
parent 30351df034
commit 1fb8a54b4b
1 changed files with 129 additions and 10 deletions
--- a/kernel.md
+++ b/kernel.md
@ -1,17 +1,119 @@
 # Kernel

-## Get and compile
- Download kernel from kernel.org
- Uncompress the archive
- `cd <linux-kernel>`
- Configure Kernel: `make ARCH=x86_64 nconfig`
-    - Config is written to `.config`
- Compile the kernel: `make ARCH=x86_64 -j <numProcesses=numCores+1>`
-    - Compressed kernel is written to `arch/x86/boot/bzImage`
+## Get and Prepare Source
+- Download kernel from <https://kernel.org>: `wget https://cdn.kernel.org/pub/linux/kernel/<kernelVersion>.tar.{xz,sign}`
+- Uncompress the archive: `unxz linux-<kernelVersion>.tar.xz`
+- Verify Signature of tar: `gpg2 --verify linux-<kernelVersion>.tar.sign`
+    - If there is a key issue, import keys: `gpg2 --locate-keys torvalds@kernel.org gregkh@kernel.org`
+- Untar the archive: `tar -xvf linux-<kernelVersion>.tar`
+- Change ownership: `chown -R jeanclaude:jeanclaude <linuxKernel>`
+- `cd <linuxKernel>`
+- Clean source: `make mrproper`

-## Run in qemu
+## Configure
+- Config is written to `.config`
+
+### For Qemu
+- Create config file `make defconfig`
+- Configure for Qemu `make kvm_guest.config`
+
+### Use Hosts Configuration
+- Copy the current hosts config: `zcat /proc/config.gz > .config`
+    - Changing `CONFIG_LOCALVERSION` is required to prevent overwriting a current kernel
+        - Can by done by setting `LOCALVERSION=-<someSuffix>` for the compile command
+- Some options may have changed, run `make olddefconfig` to accept defaults
+
+### Create own configuration
+- Configure Kernel: `make nconfig`
+
+## Compilation
+- Compile the kernel: `make -j $(nproc)`
+    - We can also choose $numCores + 1$
+- Compressed kernel is written to `arch/x86/boot/bzImage`
+- Prepare Modules: `make modules -j $(nproc)`
+- Install Modules: `sudo make modules_install`
+    - Modules are installed to `/lib/modules/<kernelVersion>`
+
+## Prepare initramfs
+- Investigate what is in the initramfs using `lsinitcpio <initramfs>`
+    - Extract to PWD using `lsinitcpio -x <initramfs>`
+
+### Using Busybox
+- Simple but has limited utilities
+```
+#!/bin/bash
+
+ARCH="x86_64"
+BB_VER="1.31.0"
+
+# Dirs
+mkdir -p root
+cd root
+mkdir -p bin dev etc lib mnt proc sbin sys tmp var
+cd -
+
+# Utils
+if [ ! -f "root/bin/busybox" ]; then
+    curl -L "https://www.busybox.net/downloads/binaries/${BB_VER}-defconfig-multiarch-musl/busybox-${ARCH}" >root/bin/busybox
+fi
+cd root/bin
+chmod +x busybox
+ln -s busybox mount
+ln -s busybox sh
+cd -
+
+# Init process
+
+cat >>root/init << EOF
+#!/bin/busybox sh
+/bin/busybox --install -s /bin
+mount -t devtmpfs  devtmpfs  /dev
+mount -t proc      proc      /proc
+mount -t sysfs     sysfs     /sys
+mount -t tmpfs     tmpfs     /tmp
+setsid cttyhack sh
+exec /bin/sh
+EOF
+chmod +x root/init
+
+# initramfs creation
+
+cd root
+find . | cpio -ov --format=newc | gzip -9 >../initramfs
+cd -
+```
+
+### Using Arch
+- Create `./mkinitcpio.conf` with following content:
+```
+MODULES=(ext4)
+HOOKS=(base systemd modconf sd-vconsole filesystems block keyboard)
+```
+- Enter fakeroot: `fakeroot`
+- Create initramfs: `mkinitcpio --generate initramfs.img --kernel <kernel> --config mkinitcpio.conf`
+    - `<kernel>` is must be located in `/lib/modules/`
+- Leave fakeroot: `exit`
+
+## Run in Qemu Step-by-Step
+- Most basic `qemu-system-x86_64 -kernel ../Kernel/arch/x86_64/boot/bzImage`
+    - Window opens with dmesg output with a panic
+- With terminal but not redirected: `qemu-system-x86_64 -kernel ../Kernel/arch/x86_64/boot/bzImage -nographic`
+- Redirect output using kernel argument: `qemu-system-x86_64 -kernel ../Kernel/arch/x86_64/boot/bzImage -nographic -append "console=ttyS0"`
+    - Still get panic as there is no root filesystem => no init to run
+- Run with initramfs: `qemu-system-x86_64 -kernel ../Kernel/arch/x86_64/boot/bzImage -nographic -append "console=ttyS0" -initrd initramfs.img`
+    - Get same panic as there is not enough RAM
+- Allocate more memory: `qemu-system-x86_64 -kernel ../Kernel/arch/x86_64/boot/bzImage -nographic -append "console=ttyS0" -initrd initramfs.img -m 512`
+    - For busybox this is all which is required
+        - For arch we get `Failed to start Switch Root.`
+    - May have increase memory quite a bit more
+- Create spares file: `dd if=/dev/zero of=kernel-hd bs=1M count=2048`
+- Create FS on virtual HD: `mkfs.ext4 kernel-hd`
+- Start using virtual HD: `qemu-system-x86_64 -kernel ../Kernel/arch/x86_64/boot/bzImage -nographic -append "console=ttyS0 root=/dev/sda rootfstype=ext4 rw" -initrd initramfs.img -m 512 -hda kernel-hd`
+Copy
+
+## Run in Qemu
 - Create dedicated folder
- Copy the kernel `<linux-kernel>/arch/x86/boot/bzImage` here
+- Copy the kernel `<linuxKernel>/arch/x86/boot/bzImage` here
 - Copy some suitable disk image here
 - Start qemu: `qemu-system-x86_64 -smp 1 -nographic -kernel bzImage -append "root=/dev/sda rootfstype=ext4 rw console=ttyS0" -hda <diskImg>`
    - `-hda`: disk image
@ -20,3 +122,20 @@
    - `-append`: command line parameters to the kernel
    - `-nographic`: disable graphic window and use command line instead
 - Quit qemu using `Ctrl-a x`
+
+### SSH Into Kernel
+- Add the following to start Qemu
+```
+-netdev user,id=unet,hostfwd=tcp::2222-:22 \
+-net user \
+```
+- Ssh into kernel usign `ssh root@localhost:2222`
+
+## Other
+- Generate JSON Compilation Database: `scripts/clang-tools/gen_compile_commands.py`
+
+# Debian/Ubuntu
+- Build for: `make -j`nproc` deb-pkg LOCALVERSION=-choose-your-prefix KDEB_PKGVERSION=$(make kernelversion)-1`
+- Install `sudo dpkg -i <out>.deb`
+- Uninstall `sudo apt remove --purge <kernelName>`
+    - Taken from list installed kernels: `dpkg --list | grep linux-image`