linux-kernel - Re: BISECTED: Re: source line numbers with x86

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Date:	Tue, 27 Jan 2009 18:41:57 -0500
From:	Mike Snitzer <snitzer@...il.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Dave Anderson <anderson@...hat.com>,
	Andi Kleen <andi@...stfloor.org>,
	Bernhard Walle <bwalle@...e.de>, Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	crash-utility@...hat.com
Subject: Re: BISECTED: Re: source line numbers with x86_64 modules?

On Tue, Jan 27, 2009 at 4:55 PM, Eric W. Biederman
<ebiederm@...ssion.com> wrote:
> Dave Anderson <anderson@...hat.com> writes:
>
>> Actually it's not a problem with the vmlinux file, but rather with kernel
>> module object files.  The crash utility has an embedded gdb module which
>> is invoked as "gdb vmlinux", and to get line numbers, the crash utility
>> simply uses the relevant built-in gdb function to get them.  And line
>> numbers work fine with the base kernel code from the vmlinux file.
>>
>> The debuginfo data of kernel modules can be subsequently added to the
>> crash session by doing a gdb "add-symbol-file" command for any or all
>> kernel modules.  But getting correct line number information for kernel
>> modules has been a crap-shoot in the past, depending upon architecture
>> and/or kernel version.  For example, they don't work with 2.6.9-based
>> RHEL4 x86_64 kernel modules, but work fine with 2.6.18-based RHEL5 x86_64
>> kernels.
>>
>> Looking at Mike's suspect kernel patch list, I don't see anything that
>> would have any relationship to the issue.  Perhaps there was a build tool
>> change during the same timeframe?
>
> It look like Mike just built a series of kernels and had a problem,
> which should preclude a tool change.

That is correct, I just built/booted/tested a series of kernels one
after the other as part of the standard git bisect procedure.  No
tools were changed.

> That said.  Does this feature of crash work in 2.6.29?  If not is
> there enough interest to track this down, and fix it if it is a kernel
> bug?
>
> If we are going to be using these tools we need them working on the
> latest and greatest kernels, not some weird enterprise branch, for
> fuddy duddies.

This feature of crash does not work with 2.6.29, nor does it work with
any kernel I've tried >= 2.6.21.  Andi Kleen shared with me that he
sees the same problem with a recent crash and 2.6.28.

AFAIK I found the regression point relative to linux (commit:
7460ed28).  The verdict is clearly still out on where the actual bug
lives (linux vs crash).

Mike
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