Re: Breakpoint meeting

[Wu Zhou <woodzltc at cn dot ibm dot com>]

Quoting Nurdin Premji <npremji@redhat.com>:


> Second method involves kprobes.
>
> When we insert the breakpoint, we know the instruction it is replacing.
> So we copy the entire instruction, put it somewhere else* in the running
> process
> Set the thread pc to point to this copy,
> single step execute,
> put pc back to where it should be after the instruction,
> and continue.

Do you mean you will use kprobe to replace the instruction at the  
breakpoint address? As far as I know, kprobe is used in kernel space.   
Maybe you meand something similar in kprobe in user space.  I know  
that there are some user-space probe proposal there, but I am not sure  
if they are mature enough for our usage.

If you could elaborate a little on this method, that will be highly  
appreciated.

> Also we have to ignore system calls because we can't do system call
> tracing and single stepping at the same time. This is apparently a
> kernel bug.

I guess the utrace mechanism Roland McGrath proposed can resolve this.  
 If it is, maybe we can re-conisder this, at least at desigh phase.   
My two cents anyway.

Regards
- Wu Zhou