Re: /dev/kmem

From: George Anzinger (george@pioneer.net)
Date: Sat May 06 2000 - 05:13:07 EST


Tigran Aivazian wrote:
>
> On Fri, 5 May 2000, Michal Kosek wrote:
> > On Fri, 5 May 2000, Tigran Aivazian wrote:
> >
> > > On Fri, 5 May 2000, Michal Kosek wrote:
> > > > I want to learn something about using of /dev/kmem.
> > >
> > > The idea of /dev/kmem is that file "offsets" in it correspond to kernel
> > > virtual addresses, so seeking to the addresses of "well-known" symbols and
> > > reading values off there gives you the values of kernel data
> > > structures. Of course, these values are not 100% self-consistent because
> > > the kernel data structures change while you are reading/writing them.
> > Yes, but how can I know what is offset of any specific structure I want to
> > read??
>
> generally, under UNIX you would use nlist(3C) on /stand/unix. Under Linux
> you get the offset by looking at System.map file or, much better, by
> using:
>
> ksymoops -s map < /dev/null
>
> and examining the map file which contains addresses of the modules'
> symbols also. If you look at lsof(8) source code, I vaguely remember it
> has some very nice interface that does the symbol manipulation for you
> which can be cut-and-pasted into your own program. Also, the MCL crash I
> mentioned contains a useful set of functions that manipulate kernel
> symbols - can be "borrowed" too as all this stuff is GPL.
 
...............snip............
Ok, the basic idea is to look at the System.map file right?

Now I am doing a lot of kernel testing and have more than one kernel on
a system, using lilo to pick and choose. What is the usual method used
to insure that the correct System.map file is avaiable to each system?
I assume one set up a link to it at boot time, but how is this usually
organized? For example, in my case I download the new kernel to the
test system, run lilo and then reboot. I assume I should also download
the System.map file, but how does the boot script know which system
booted?

George

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