Re: PA specifies invalid T_ADAFLAGS

[Matthew Wilcox <willy@debian.org>]

On Wed, Apr 24, 2002 at 10:59:13PM -0400, Robert Dewar wrote:
> > I suspect using "-mdisable-indexing" dates from a time when indexing
> > didn't work very well.  This was reworked a year or two ago.
> 
> No, this is definitely needed for Ada, due to its use of virtual array
> indexing, which otherwise fails on the PA, due to its odd segmentation
> semantics.

Hmm... could you be a little more specific?  I suspect this may not be an
issue for hppa-linux.  For those who are unfamiliar with what's going on,
a potted summary:

PA has 8 space registers numbered 0 to 7.  Most instructions allow you
to specify one of 1, 2 or 3, OR to select the space register to use based
on the top two bits of the virtual address.  If the top two bits are 00,
use sr4, 01, use sr5, 10 uses 6 and 11 uses 7.  HPUX takes advantage
of this to map all shared libraries in one quadrant, program text in
another quadrant and program data in a third and fourth.  Linux does
no such thing and programs space registers 4 to 7 with the same value.
So anything can be mapped anywhere and programs appear to have a flat
address space.  As long as the compiler doesn't decide to generate an
instruction specifying sr 1, 2 or 3 -- and there's no reason it should --
you can pretty much ignore the segmentation in userspace on Linux/PA.

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