I found the following 2 problems:
1) smp.c: the file contains an "extern unsigned long start_kernel",
but start_kernel is a function.
The variable is never used, I've removed the extern.
2) setup.c: setup_arch() contains a "smp_trap", but
the function is never called twice: initialize_secondary()
[called from start_kernel() before setup_arch()] cannot return.
I've attached my patch (against 2.2.6).
I've tested it on my SMP computer (MPS 1.1).
Regards,
Manfred
patch_cleanup-2.2.6