linux-kernel - kgdb issues in 2.6.26.5-rt9

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Date:	Sun, 5 Dec 2010 00:04:37 -0800 (PST)
From:	Tal Lubko <tallubko@...oo.com>
To:	linux-kernel@...r.kernel.org
Subject: kgdb issues in 2.6.26.5-rt9

Hello all,

I am running a custom 2.6.26.5-rt9 kernel which is the 2.6.26.5 vanilla kernel 
with version 9 of the real time patch for that specific version. I am trying to 
debug a "hard" problem which means not a problem which is easily reproducibe, 
appears only on boot, only under certain conditions etc. In order to debug the 
problem I am using kgdb.

Before anyone flames me, I am aware that kgdb is not the highway as far as 
kernel debugging is concerned, but due to certain external factors I am 
interested in making that approach work.

My understanding of the kgdb status (please correct me if I am wrong on any of 
the following...):
- kgdb is supported in 2.6.26.5 vanilla and the important stuff works.
- the version of kgdb in 2.6.26.5 is the "light" version by Ingo, Thomas and 
Jason which means that some features are missing.
- I am not aware of any limitations of the host side gdb that I am supposed to 
use in order to debug the target (I tried using 6.6 and 6.8)

The problems I have with kgdb:
- info threads shows most of the threads on the system but then hangs for a 
short time with various data errors. As a first stab this seems like a protocol 
issue between host and target.
- thread [tid] does not work. It claims that the thread ids that I use do not 
exist although the info that I do manage to get out of "info threads" admits 
that they do. ps(1) on the target also confirms the thread id numbers.
- I haven't managed to set breakpoints. For instance: breaking on printk using 
"break printk" results in a segv of the debugger (huh?!?). This looks like a gdb 

protocol issue between the host and target which brings me back to the issue of 
whether there are limitations on the version of gdb to be used.

Please CC me on any replies since I am not subscribed.

Thanks in advance,
Tal

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