[parisc-linux] a todo entry

[Matthew Wilcox]

On Thu, Oct 11, 2001 at 05:52:59AM -0400, Jurij Smakov wrote:
> > #define KERNEL_DS 0
> > #define USER_DS mfsp(3)
> > #define get_ds() (KERNEL_DS)
> > #define get_fs() mfsp(2)
> > #define set_fs(x) mtsp(x, 3)
> 
> I've been looking at it for the last two days and I still
> cannot understand it :-). Why do You want set_fs to write to
> sr3?

That was a mistake -- should be #define set_fs(x) mtsp(x, 2)

> a) In userspace sr2 is always 0, so that everybody can make 
>    their syscals.
> b) sr2 is set to sr3 when we enter the kernel.
> c) get_fs returns sr2 and set_fs sets sr2, so that we can
>    always use sr2 as the space in __get_user/__set_user
> d) When we return to userspace from the kernel, sr2 is
>    set to 0 again.

Yes.

> While modification of uaccess.h to satisfy c) is more or less
> trivial, real problem for me is b) and d). I'm not quite sure, 
> where to look for these entries and returns? I would guess, 
> entry.S is the right place, but obviously I didn't RTFM enough to
> hack it yet.

Right.  I suspect the only place(s?) we need to set sr2 to 0 is where we
set sr4-7 to the user's space ID, and set sr2 to sr3 in the same places
we set sr4-7 to 0.  But that theory needs setting up and testing...

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