Re: [uml-user] What are you using UML for?

[Daniel P. <phi...@in...>]

On Mon, 11 Dec 2000, Jeff Dike wrote:
> I'm writing an article for Linux Magazine about UML.  One of the things I'd 
> like to talk about is how people are using UML.  So, if you're currently using 
> it for something, are evaluating it for some purpose, or think you might 
> possibly be interested in using it for something in the indefinite future, I'd 
> like to hear about it.

You know what I'm using UML for: kernel hacking.  It's working out
pretty well - my earlier post on l-k summarzized the development cycle
advantages.

Yesterday I did something pretty sophisticated with semaphores
between threads and I was able to develop and debug it completely under
UML.  There weren't any bugs in this case, but still, I didn't have to
boot a test machine to verify that.  When I did boot the test machine,
this code worked exactly as it did in UML.

Not only that, but I can make diffs of my work against a clean UML tree
and the resulting patch applies cleanly to the normal kernel tree.  I'm
actually surprised this works so well, and I'm reading your patch
now to find out why.  Of the 4,000 lines I've looked at so far, most
deal with the block layer, console I/O, thread startup and other things
I'm not working on.  It's a safe guess that UML wouldn't be a lot of use
for debugging the Linux thread mechanism itself, but so long
as I stay away from such parts of the system that you've modified -
and that doesn't seem to be very many - then I can keep extracting my
patches directly from UML.

Today I'm moving on to running Tux2 on UML.  Up to now I've been using
the time-honored printk/oops method of debugging Tux2, with modules to
make it less painful.  Under UML I should compile Tux2 directly into
the kernel so I don't have to deal with the module symbol loading
on every test cycle.

Working with modules isn't any harder under UML than normal Linux, but
it's much less convenient for debugging than non-module code.  And
actually I'd prefer to stick with modules if I could.  So I'd like it
very much if we could put our heads together and come up with a way of
loading getting gdb to load the module symbols automatically.  I know
it's hard :-).

-- 
Daniel