skas understanding

uml-devel Nicolas Blanc 2 participants 2 messages Mar 30, 2004 User-mode Linux (UML)

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Nicolas Blanc

author

2004-03-30 11:27 UTC #0 lore raw

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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Jeff Dike

2004-03-30 16:33 UTC #1 lore raw

Quoted 1 line · [email protected] said:

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

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

Quoted 1 line

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.

Quoted 1 line

3) Where is the kernel thread?

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

Jeff