Re: Size of pointers in sys_call_table?

[Andi Kleen <ak@suse.de>]

Alan Cox <alan@lxorguk.ukuu.org.uk> writes:

> > The layout of the sys_call_table is totally architecture dependant.  The
> > question to ask here is why do you need to use it?  Modifying it to hook
> > into syscalls is frowned upon.
> 
> And potentially unsafe (think about caching, and non atomic writes on
> some platforms)

It is ATM impossible to make a module that patches sys_call_table safe against
module unload races. The only way is to put a stub into the main kernel
that manages the module counters and calls a separate hook (i.e. as done 
by nfsd's syscall) 

[Introducing quiescent states in module unloading would probably fix that,
as it has been discussed for a long time now, but I lost hope that it'll ever
get implemented in the main kernel]

Other than that on some weird architectures like IA64 it can get quite 
complicated to patch the syscall table.

-Andi