[uml-devel] skas understanding

[uml-devel] skas understanding

[Nicolas Blanc]

Hello,
I am trying to figure out how does UML run in skas mod (I already red some
papers abouts it and now I d'like to jump into the code),
but I am experiencing some difficulties about things that are done in
function start_uml_skas :

1)  in function start_userspace :

    stack = mmap(...,MAP_ANONYMOUS,...);
    ...
    pid = clone(userspace_tramp, (void *) sp,
            CLONE_FILES | CLONE_VM | SIGCHLD, NULL);
    ...
    munmap(stack,PAGE_SIZE);

I don't understand the purpose of using anonymous mmap.

2) capture_signal_stack() : what is it for ?

3) Where is the kernel thread?

Thanks

Nicolas



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Re: [uml-devel] skas understanding

[Jeff Dike]

nicolas.blanc@epfl.ch said:
> I don't understand the purpose of using anonymous mmap.

If you want a random piece of memory, it needs to be anonymous.

> 2) capture_signal_stack() : what is it for ?

It's broken and is going to change, but it grabs a host signal frame so it
can later copy it, with modifications, to its own processes stacks when they
receive signals.

> 3) Where is the kernel thread? 

start_uml_skas, it spends most of its time in the various invocations of
userspace().

				Jeff



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