RISC architectures were not meant to be programmed by humans in
assembly language!

The ACIS 4.2 file /usr/doc/42a/linkage.t describes the 4.2/RT linkage
convention.  The file EXCHJ.c contains C++ versions of the support
routines required by the OOPS Process class: Process::create() and
Process::exchj().  These C++ routines don't actually work because
special registers such as the stack pointer (sp) and frame pointer
(fp) must be manipulated, and there is no way to do this in C++.
However, compiling this file produces an assembly language version
(EXCHJ.s) which can be edited by hand to use the appropriate special
registers.  This is how the file exchj.s was produced.
