Re: Tracepoints on gdb/gdbserver

[Ramana Radhakrishnan <ramana.radhakrishnan@codito.com>]

On Wed, 2003-10-01 at 04:12, Jim Blandy wrote:
> Daniel Jacobowitz <drow@mvista.com> writes:
> > That'll work.  I got the impression that tracepoints are designed to be
> > even lighter-weight than that; you can implement them via an agent
> > expression -> native assembly conversion.  But this requires runtime
> > patching and is quite complicated.  Just saving the overhead of the
> > remote protocol will be useful.
> 
> Yes.  The original implementation used a bytecode interpreter (which
> is really pretty fast), but it was an embedded board with no OS, and
> the interpreter ran in the same address space as the program being
> debugged, so those memory references were just load instructions, and
> the trace opcodes were just memcpy calls.
> 
> If you implement tracepoints in gdbserver, then those are going to
> become ptrace calls, which are going to be a lot slower.  It might
> still be fast enough for your purposes --- but I just want to point
> out that it's not the same arrangement we used in the original
> application.

 I agree that it would be slow but as Daniel points out, compared the
overhead of the remote protocol, it would still be useful.

regards
Ramana