Subject: Re: vtopte() problems
To: ycchang <email@example.com>
From: Nathan J. Williams <firstname.lastname@example.org>
Date: 05/20/2003 14:53:23
"ycchang" <email@example.com> writes:
> this inline funtion returns PTE_BASE + i386_btop(va) , where
> PTE_BASE = 0xbfc00000 and i386_btop(va) is defined as
> ((unsigned)(x) >> PGSHIFT). That is to say it gets the VA of PTE
> corresponding to a VA.
> So , should vtopte() return PTE_BASE + i386_btop(va)*4?
It does. The definition of PTE_BASE is the value 0xbfbc0000 cast to a
pointer, a pt_entry_t *. The pointer type causes the addition to
follow the usual C rules for pointer arithmetic, which means that the
value returned from i386_btop() is interpreted as a number of
pt_entry_t's. Since a pt_entry_t is 4 bytes (see pte.h), the scaling
is implicit in the pointer math.