How to Cross-Build Debian/MIPS Kernel

Background

I was trying to install Debian/MIPS on QEMU and found out that I need to build/update the kernel. The existing instructions mostly talk about native build, which is painfully slow on QEMU. I tried once and it took almost 10 hours! There are some references to cross-build debian kernel and none applies straightforwardly. I decided to write a blog on how I did it.

Prepare the host

• My host is Ubuntu 18.04
• I'm building 64bit MIPS little endian kernel for malta board
• Need install a build related packages :
  • apt install -y build-essential linux-source bc kmod cpio flex cpio libncurses5-dev bison libssl-dev
• Need to install crosscompile tools. Fortunately we only need gcc and binutils for compiling kernel
  • apt install -y binutils-mips64-linux-gnuabi64 gcc-mips64-linux-gnuabi64

Set up the source

• Download and unpack kernel source and config from debian site
  • cd download
  • wget http://security.debian.org/debian-security/pool/updates/main/l/linux/linux-source-4.19_4.19.67-2+deb10u2_all.deb
  • wget http://security.debian.org/debian-security/pool/updates/main/l/linux/linux-config-4.19_4.19.67-2+deb10u2_mips64el.deb
• Extract the kernel source from .deb file
  • dpkg -x download/linux-source-4.19_4.19.67-2+deb10u2_all.deb .
  • tar xf usr/src/linux-source-4.19.tar.xz
• Copy and modify the kernel config as you see fit
  • dpkg -x download/linux-config-4.19_4.19.67-2+deb10u2_mips64el.deb .
  • unxz usr/src/linux-config-4.19/config.mips64el_none_5kc-malta.xz
  • patch -p0 -b < kconfig.patch
  • cp usr/src/linux-config-4.19/config.mips64el_none_5kc-malta linux-source-4.19/.config
• Make deb packages for kernel
  • cd linux-source-4.19
  • make ARCH=mips CROSS_COMPILE=mips64-linux-gnuabi64- oldconfig
  • make ARCH=mips CROSS_COMPILE=mips64-linux-gnuabi64- KDEB_PKGVERSION=1 -j`nproc` bindeb-pkg

Download the source

Below the script file and kernel config patch would work together to execute the above steps automatically.

• kernel config patch
• build script