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Re: PA specifies invalid T_ADAFLAGS
- From: "John David Anglin" <dave at hiauly1 dot hia dot nrc dot ca>
- To: willy at debian dot org (Matthew Wilcox)
- Cc: dewar at gnat dot com, gcc at gcc dot gnu dot org, willy at debian dot org
- Date: Thu, 25 Apr 2002 00:27:03 -0400 (EDT)
- Subject: Re: PA specifies invalid T_ADAFLAGS
> 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
The first model is only available under hpux using assembly language.
The standard code generated by gcc uses sr4 which causes the top two
bits of a virtual address to select one of sr4, sr5, sr6, or sr7,
respectively.
Your comments that the base register can end up in the wrong segment
still suggests a bug to me. I can't imagine the linker working with
anything other than the standard runtime. As I said, a fix was done
regarding which register becomes the base register. There were
problems in the past with the index being selected as the base register
and that didn't work with the segmented architecture of the PA.
I agree with Matthew that "-mdisable-indexing" should not be used
under linux as it has a flat memory model.
There doesn't seem to be any documentation of why -mdisable-indexing
is needed and nothing in the changelogs. If there is something
special about the memory model used by ada, it would be good to
have it documented.
Dave
--
J. David Anglin dave.anglin@nrc.ca
National Research Council of Canada (613) 990-0752 (FAX: 952-6605)