I need to compile the kernel (because of more than 4 UARTS in my machine and to use UIO for proprietary hardware) in TinyCore 5.0.1.
However I already found some traps before I even could type 
make.
Found the how-to at 
http://wiki.tinycorelinux.net/wiki:custom_kernel, but it dose not really describe the files found at 
http://tinycorelinux.net/5.x/x86/release/src/kernel/ - "patched" seems quite obvious, but maybe the how-to could benefit from a rework?
Next I downloaded 
linux-3.8.13-patched.txz and tried to unpack with 
tar - which unpacks some files but stops with 
"short read"  - in spite of the fact that the txz is intact.
Tried it with t
ar.tcz (1.26) from the 
apps installed - stopped at a different point with the same error message...
Tried it with 
linux-3.12.2.tar.xz from kernel.org - same problem.
When I finally tried to unpack
 linux-3.12.2.tar.xz with 
xz it seemed to work - at least it finished without error.
However when I used 
xz on 
linux-3.8.13-patched.txz it left me with a tar-file. On this tar-file the 
tar from TinyCore seemed to work OK then.
Am I overlooking the obvious or doing something wrong here?
BTW: I found some older discussions on a bug of the 
xz embedded in tiny core causing a "short read" error - on the other hand 
xz seemed to finally work for me?