breakpoint assistance: single-step out of line

[Frank Ch. Eigler]

Roland McGrath <roland@redhat.com> writes:

> The method of single-stepping over an out of line copy of the
> instruction clobbered by breakpoint insertion has been proven by
> kprobes.  The complexities are mitigated in that implementation by
> the constrained context of the kernel and the fixed subset of
> possible machine code known to validly occur in any kernel or module
> text.

Another important aspect is that userspace may be hostile.  Beyond
just containing oddball instruction sequences, it may deliberately
rewrite its own .text, or otherwise interfere with probing in order to
produce crashes or security breaches.

- FChE