Re: [RFC] gelf - user space probe debugger

[Jiri Olsa <jolsa at redhat dot com>]

On Tue, Jan 25, 2011 at 06:35:40AM +0800, Yao Qi wrote:
> On 01/25/2011 12:10 AM, Jiri Olsa wrote:
> > hi,
> > 
> > I started a debugger project.  It's based on the user space backport
> > of optimized kprobes (djprobes) and RSP stub implementation.
> > 
> 
> First of all, it is a nice piece of work!
> 
thanks

> > The debugger is implemented as a preloaded shared library,
> > which handles all the debugger work, hence no kernel ptrace
> > is needed.
> 
> Here are some questions, and I am sorry if my questions go out of scope
> here.
> 1. Do you plan to handle signal without ptrace support?  In
> ptrace-debugger, we can know every signal delivered to debuggee process.
>  How can we do that in your probe-debugger?

haven't thought about that, but I guess the only option would be to
take over the signal handlers and somehow call the user handlers.. also
intercept the signal handling routines (signal/sigaction..) ..seems tricky ;)

> 
> 2. Do you plan to support hardware single-step on x86?
> 

I haven't thought that far ahead.. looks like it might be possible via
setting the TRAP flag and handling SIGTRAP

> > 
> > I'd like to ask for opinions if there'd be users for such thing,
> > and if it's worth to continue on this..
> 
> AFAIK, it is not easy to replace ptrace-based debugger by probe-based
> debugger completely.  However, probe-based technology can be a
> complementary part to existing ptrace-based debugger, especially to
> efficient implementation of breakpoint/watchpoint/tracepoint in some
> cases.  Shortly, it is good to put both ptrace-based and probe-based
> into single debugger, and maximize their advantages, and minimize their
> disadvantages.

yep, makes sense, I'll think about it.. thanks a lot for feedback

jirka