Re: Making "info thread" sane

[Andrew Cagney <cagney@gnu.org>]

> On Wed, Mar 03, 2004 at 08:01:58AM +0200, Eli Zaretskii wrote:
> 
>>>> > Date: Tue, 02 Mar 2004 16:14:35 -0800
>>>> > From: George Anzinger <george@mvista.com>
>>>> > 
>>>> > Andrew Cagney wrote:
>>>
>>>>> > > Um, can you explain the problem?
>>>
>>>> > 
>>>> > The problem is that, for most threaded apps and for the kernel which treats each 
>>>> > task as a thread, the "info thread" command gives a list of threads all stopped 
>>>> > in the context switch code.  What is desired is to do one or more "up" commands 
>>>> > and report info on this location.

>>> Can you explain why GDB should know about this?  The user could
>>> always "up" manually or via the GDB's scripting language, right?
>>> 
>>> As I see it, the situation is analogous to when you, e.g., attach GDB
>>> to a running process, and the backtrace shows that it is stuck in
>>> some uninteresting system call.  The very next thing to do is either
>>> "up" or step the program until it winds up in some application code
>>> that _is_ interesting.  We don't request GDB to show the application
>>> code automagically, do we?

Right.  Commands like:

info threads
thread 1
info frame

should all give consistent output.  As they say, don't lie to the user.

> The interesting thing about George's situation is that there's a lot of
> threads (basically, all but one of them) that we know in advance will
> be stuck in context switching code.  One of the nice things about info
> threads is that it shows you the current frame for all your threads;
> but in this case, that's not really very interesting information.

> If we could find out where those threads were _before_ they switched
> out, now, that would make for an interesting overview.

It should be possible to script this (I suspect it isn't and hence part 
of the problem).   For instance something like:

(gdb) define kthread-info
   thread apply all try
     set $skip 0
     if $frame.func == &func you want to ignore
       set $skip = $skip + 1
     end
     silent up $skip
     thread info
     silent down $skip
   end
end

There are patches for "try" and "$func" lurking, silent is easy (if it 
makes sense).  Wonder if the parser allows "thread apply all try ...end"

I know other kernels have, over time, accumulated a bunch of scripts for 
dumping out internal structures in human readable form.  I think this 
goes into that category.

enjoy,
Andrew