Re: Yet another crash in FreeBSD 5.1

On Saturday,  2 August 2003 at 18:36:24 -0700, Terry Lambert wrote:
> Greg 'groggy' Lehey wrote:
>>> The information I gave him gets him to lines of source code, instead
>>> of just function names with strange hexadecimal numbers that resolve
>>> to instruction offsets that may be specific to his compile flags,
>>> date of checkout of the sources from CVS, etc..
>>
>> The first step of the link above does the same thing.  But it's only
>> the first step.
>>> by eyeballing the lines of source code in question and understanding
>>> the code around it well enough that you can tell *how* a pointer
>>> there could be NULL.  My instructions *get* him those lines of
>>> source.
>>
>> You obviously still haven't read the reference.  Do that first, and
>> come back when you have either understood things or are having
>> difficulty understanding.  But don't shoot off your mouth without
>> knowing what's going on.
>
> I read the reference.
>
> How does it apply in cases like this one, where you don't have a
> vmcore file?

You don't seem to have read the reference very well.  It also asks for
other supporting information.  That's the most important thing at the
moment.  I know that because I've been there before, and I've looked
at a number of these dumps: it's almost certainly related to something
he's doing which is not normal.  You don't know that, and that's
excusable, but it's not excusable that after four or five requests,
you still haven't RTFM'd.

> The way I would approach finding this, with only:
>
> 1)	The line of code where the failure occurred
> 2)	The stack traceback, with no arguments
> 3)	The sources for the code in the stack traceback
>
> would be to eyeball the code in #1, and try to figure out how
> I gould get to that point with that pointer having a NULL value,
> given my apriori knowledge of the forward call graph.

You have that?

> I would examine every intermediate conditional and function call
> that could effect the value of the pointer and cause it to be NULL
> at the point in question.

Go for it.  Once I get the log files, I'll start there.

> One of the details I wish you would check is whether or not he has a
> vmcore file, or the ability to get one...

We'll address that issue when it becomes necessary.

Greg
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