[plug] System.map

[Senectus -]

To quote a rather annoying Advert "BRILLIANT"

thanks for an excellent explanation :-)

Senectus

--
“I don’t think Bastard goes anywhere near to describing the unmitigated scum 
sucking, bottom feeding toerag that is me. But hey – who knew shit could be 
worth so much…”  - Simon Travaglia BOFH (Could have easily been Darl McBride 
that said it though)


>
>On Wed, May 19, 2004 at 11:28:05AM +0000, Senectus - wrote:
> > This might seem like a silly question.. but what is the file 
>"System.map"
> > used for ?
>
>It tells various programs on your machine what the addresses of
>symbols (functions and variables) are in kernel space. Why would
>they need to know? Programs like ps can find out what system call a
>process is currently stuck in (see ps -o wchan) - it does this by
>looking in /proc/<pid>/stat for the address of the system call, and
>then looks that up in System.map. This is why ps often complains
>when System.map isn't about or up to date.
>
>If you're doing kernel debugging and you have an Oops, Panic, or
>other random part of the kernel that prints out a stack trace,
>ksymoops will use System.map to find out in exactly which function
>in kernel space that things went awry. If you want to submit an oops
>to any kernel hacker, the first thing they'll do is ask you to pass
>it through ksymoops. The oops is meaningless otherwise, as the
>values are highly dependent on precisely how you compiled your
>kernel.  Hence even ksymoops's output is meaningless if your
>System.map is not the exact same one for the kernel that generated
>the oops.
>
>In short, it's probably not much use in day to day work, but for
>debugging, or for finding out where a process is hanging or what
>it's doing, it's very useful! You could use strace to do the latter,
>but not if you don't own the process ;)
>
>*deep breath*
>
>Hope this sheds some light and hasn't confused you entirely :)
>
>Bernard.
>
>--
>  Bernard Blackham <bernard at blackham dot com dot au>
>_______________________________________________
>PLUG discussion list: plug at plug.linux.org.au
>http://mail.plug.linux.org.au/cgi-bin/mailman/listinfo/plug
>Committee e-mail: committee at plug.linux.org.au

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