To make UML build and run on s390, I needed to do these two little
changes:

1) UML includes some of the subarch's (s390) headers. I had to
   change one of them with the following one-liner, to make this
   compile. AFAICS, this change doesn't break compilation of s390
   itself.

2) UML needs to intercept syscalls via ptrace to invalidate the syscall,
   read syscall's parameters and write the result with the result of
   UML's syscall processing. Also, UML needs to make sure, that the host
   does no syscall restart processing. On i386 for example, this can be
   done by writing -1 to orig_eax on the 2nd syscall interception
   (orig_eax is the syscall number, which after the interception is used
   as a "interrupt was a syscall" flag only.
   Unfortunately, s390 holds syscall number and syscall result in gpr2 and
   its "interrupt was a syscall" flag (trap) is unreachable via ptrace.
   So I changed the host to set trap to -1, if the syscall number is changed
   to an invalid value on the first syscall interception.
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!