make -j4 breaks the kernel uClinux process

Learned a lesson the hard way today and thought I would share to prevent others from the same mistake.

On the wiki pages, the page that explains how to build the tool chain suggests using "make -jx" where x is the number of cores on your build platform+2.

So I decided to speed up the kernel and root file system build process with the same trick, substituting "make -j4" for plain make.

Long story short, this breaks the root file system.

I did a clean kernel build from scratch:

git clean -f -x -d

make menuconfig (select default all selections and lose changes)

make vendor_hwselect SYSPTF=/path/to/ptf

make -j4

The resulting zImage booted just fine but gave a kernel panic about being unable to mount root file system.

Repeating the exact steps as above with plain "make" instead of "make -j4" gave a kernel plus root file system that worked fine.

That will teach me to follow directions... I lost a day trying to figure out why my system would not boot anymore :(