fun things mapped into user space

[terryl at sail.LABS.TEK.COM]

In article <25870 at uflorida.cis.ufl.EDU> kml at mosquito.cis.ufl.edu (Kevin Lahey) writes:
>I noticed, while perusing various bits of /usr/include/sys on our SGI IRIS,
>running IRIX 3.3.1, that there are some interesting things mapped into the
>user space.  For instance, at 0x00200000, there is a little structure with
>my pid, and info set up for shared group scheduling.
>
>IRIX is a System V derivative, with many enhancements (I suppose I'll be 
>corrected if I'm mistaken :-)).   Is this a normal thing to find?  Are there
>all sorts of interesting things just floating around out there, waiting 
>for me to find 'em?  How about under BSD?  SunOS?  How do I find 'em?
>A quick look through Bach and the 4.3 book doesn't seem to turn up anything,
>other than the fact that the u-area is mapped in...


     Careful with that U-area mapping!!! It's highly machine dependent, and
works best with just one linear address space for both user and stupidvisor
mode (i.e. like the VAX); it's a little more tricky (but definitely doable)
on a machine with separate address spaces for both user and stupidvisor mode;
you just have to give up a little of your measly 2-4 Gig address space for it!!

     As a rule, it's really hard to predict what's mapped in and what's not;
it's very system specific. For example, on some of our systems at Tektronix
we map in what's called a soft configuration structure. It contains such
assorted goodies as amount of physical memory, number and type (as far as it
can determine) of disk drives, type of display, width and depth of display,
other such I/O cards, etc.

__________________________________________________________
Terry Laskodi		"There's a permanent crease
     of			 in your right and wrong."
Tektronix		Sly and the Family Stone, "Stand!"
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