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Re: [TESTCASE] Minimized testcase for AltiVec segfault
- From: Kumar Gala <kumar dot gala at motorola dot com>
- To: Aldy Hernandez <aldyh at redhat dot com>
- Cc: Daniel Egger <degger at fhm dot edu>, GCC Developer Mailinglist <gcc at gcc dot gnu dot org>
- Date: Wed, 27 Feb 2002 17:39:28 -0600 (CST)
- Subject: Re: [TESTCASE] Minimized testcase for AltiVec segfault
> 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 saved
on a context switch).
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 one's
code (for SVR4 style register allocation).
If GCC is managing VRSAVE when -mabi=altivec then I think there should be
another flag to disable the use of VRSAVE. It tends to be a waste of time
to manage as well as hard to use for determining which regs to save by the