The “Kernel builder” is a set of attributes available on the mobile-nixos attribute overlaid on top of Nixpkgs.

mobile-nixos.kernel-builder
mobile-nixos.kernel-builder-clang_9
mobile-nixos.kernel-builder-gcc49
mobile-nixos.kernel-builder-gcc6

At the base level, they are made available pre-versioned with a compiler-specific stdenv so that OEM kernels requiring a specific compiler to either build or boot can use the right compiler version.

The kernel builder additionally provides configuration options to work with common quirks in kernel builds.

Choosing the right builder

There is no clear and fast rule for this. The most likely suggestion is to look at the kernel version string for a kernel built from the sources you are using. It should describe the compiler being used.

Another way to figure out which builder to use is to compare kernel derivations either for devices using the same SoC. It often happens that basic quirks like requiring specific compilers are rooted in changes from the first party that forked the kernels, the SoC vendor.

Choosing quirks

isQcdt

When true, the build will use dtbTool to build a QCDT device-tree image.

By default it will use the FDTs from the appropriate arch/*/boot folder from the kernel build. The directory to use can be changed using qcdt_dtbs.

isExynosDT

When true, the build will use dtbTool-exynos to build a device-tree image for the device.

By default it will use the FDTs from the appropriate arch/*/boot/dts/ folder from the kernel build. The pattern to use can be changed using exynos_dtbs.

Additionally, the platform code and subtype codes can be configured with exynos_platform and exynos_subtype, though the default are likely to work.

isImageGzDtb

When true, the build will enable support for android-specific "Image.gz-dtb" appended images.

It is most likely this is needed if isQcdt is not used for Android-based devices.

isCompressed

Set to the compression algorithm for the kernel. For the time being only "gz" or false are valid values. By default it is "gz".

enableRemovingWerror

Goes through all Makefile files from the kernel source tree and removes the instances of -Werror.

This is generally used when building a kernel with a newer compiler than which was used when the kernel was authored.

enableCompilerGcc6Quirk

When true, a compiler-gcc6.h is added to the expected location for the kernel build. This is generally only needed for older kernels.

When enabled, the kernel source will be patched to force only one instance of the logo to be shown, and centered on the display.

This is used to provide a graphical element before the stage-1 init is running.

This is enabled by default. Note that on some systems the feature does not work even when enabled. Keep it enabled as it is a no-op.

enableLinuxLogoReplacement

When enabled, the file linuxLogo224PPMFile points at will be used to replace the drivers/video/logo/logo_linux_clut224.ppm file in the kernel source tree.

This effectively replaces the Tux logo.

By default an appropriate file is provided by Mobile NixOS.

enableCompilerGcc6Quirk

When enabled, building and installing is done in one single step. Some kernels, mainly prior to 4.4, will rebuild the kernel from scratch when installing. Work around the issue by using only one make invocation.

This defaults to true for kernel versions prior to 4.4.

Using the wrong value can either:

  • be a no-op

  • make the build take twice as long

  • fail the build in obvious ways

There have been no weird side-effects observed when using the wrong value. Touching this value, other than outright failing the build, will not make a kernel that doesn’t boot otherwise boot.

Making a new port

There is no porting guides yet. The current recommendation is to look for a kernel derivation from a device using the same or a similar SoC and use it as a starting point.