[$] Modifying another process's system calls

The ptrace()
system call allows a suitably privileged process to modify another in a
large number of ways. Among other things, ptrace() can intercept
system calls and make changes to them, but such operations can be fiddly
and architecture-dependent. This patch series from
Dmitry Levin seeks to improve that situation by adding a new
ptrace() operation to make changes to another process's system
calls in an architecture-independent manner.