Reducing the Linux kernel image size

Before or in parallel with the root filesystem customization, embedded projects usually require an image size optimization that will reduce the boot time and memory usage.

Smaller images mean less storage space, less transmission time, and less programming time, which saves money both in manufacturing and field updates.

By default, the compressed Linux kernel image (zImage) for the wandboard-quad is around 5.2 MB. This recipe will show how we can reduce that.

How to do it...

An example of a minimal kernel configuration for a Wandboard that is able to boot from a microSD card root filesystem is the arch/arm/configs/wandboard-quad_minimal_defconfig file that follows:

CONFIG_KERNEL_XZ=y
CONFIG_NO_HZ=y
CONFIG_HIGH_RES_TIMERS=y
CONFIG_BLK_DEV_INITRD=y
CONFIG_CC_OPTIMIZE_FOR_SIZE=y
CONFIG_EMBEDDED=y
CONFIG_SLOB=y
CONFIG_ARCH_MXC=y
CONFIG_SOC_IMX6Q=y
CONFIG_SOC_IMX6SL=y
CONFIG_SMP=y
CONFIG_VMSPLIT_2G=y
CONFIG_AEABI=y
CONFIG_CPU_FREQ=y
CONFIG_ARM_IMX6_CPUFREQ=y
CONFIG_CPU_IDLE...