Each time you build a kernel image, the kernel source code is fetched and unpacked into the following directory:
${S}/linux
See the "Finding the Temporary Source Code"
section and the
S
variable
for more information about where source is kept during a build.
For this example, we are going to patch the
init/calibrate.c
file
by adding some simple console printk
statements that we can
see when we boot the image using QEMU.