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Re: [TESTCASE] Minimized testcase for AltiVec segfault
- From: Aldy Hernandez <aldyh at redhat dot com>
- To: Kumar Gala <kumar dot gala at motorola dot com>
- Cc: Daniel Egger <degger at fhm dot edu>, GCC Developer Mailinglist <gcc at gcc dot gnu dot org>, David Edelsohn <dje at watson dot ibm dot com>, Geoff Keating <geoffk at geoffk dot org>
- Date: Thu, 28 Feb 2002 13:14:34 +1100
- Subject: Re: [TESTCASE] Minimized testcase for AltiVec segfault
On Thursday, February 28, 2002, at 10:39 AM, Kumar Gala wrote:
>> how about vrsave? surely you need vrsave to be set properly, otherwise
>> the OS will not save your vector registers on a context-switch.
> Does -mabi=altivec cause VRSAVE to be updated?. On Linux, VRSAVE is not
> used by the OS to determine which registers to save (all vr regs are
> on a context switch).
hmm, when i first started coding, i talked to a few linux kernel hackers
and no one was able to tell me wether linux used vrsave or not.
should've talked to the ppc maintainer ;-)
> VRSAVE is useful for ABIs which allocate registers in order (ie MacOS)
> such that one can mark the last used register and save/restore to that
> point. Otherwise it seems rather painful to manage/update vrsave in
> code (for SVR4 style register allocation).
ahh, that wasn't clear from the specs.
> If GCC is managing VRSAVE when -mabi=altivec then I think there should
> another flag to disable the use of VRSAVE. It tends to be a waste of
> to manage as well as hard to use for determining which regs to save by
> context code.
in which case... you are correct. we should add a flag to not set
ahhhctually, i motion we get rid of -mabi=altivec and have -maltivec
imply an abi enhancement. unless geoff/david or someone else can
think of a reason not to.
Aldy Hernandez E-mail: email@example.com
Professional Gypsy Lost in Australia
Red Hat, Inc.