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Re: [RFC PATCH 00/29] arm64: Scalable Vector Extension core support
- From: Szabolcs Nagy <szabolcs dot nagy at arm dot com>
- To: Dave Martin <Dave dot Martin at arm dot com>, Florian Weimer <fweimer at redhat dot com>, Yao Qi <qiyaoltc at gmail dot com>
- Cc: <nd at arm dot com>, <linux-arm-kernel at lists dot infradead dot org>, <libc-alpha at sourceware dot org>, Ard Biesheuvel <ard dot biesheuvel at linaro dot org>, Marc Zyngier <Marc dot Zyngier at arm dot com>, <gdb at sourceware dot org>, Alan Hayward <alan dot hayward at arm dot com>, Torvald Riegel <triegel at redhat dot com>, Christoffer Dall <christoffer dot dall at linaro dot org>
- Date: Wed, 30 Nov 2016 12:22:32 +0000
- Subject: Re: [RFC PATCH 00/29] arm64: Scalable Vector Extension core support
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On 30/11/16 12:06, Dave Martin wrote:
> For setcontext/setjmp, we don't save/restore any SVE state due to the
> caller-save status of SVE, and I would not consider it necessary to
> save/restore VL itself because of the no-change-on-the-fly policy for
> this.
the problem is not changing VL within a thread,
but that setcontext can resume a context of a
different thread which had different VL and there
might be SVE regs spilled on the stack according
to that.
(i consider this usage undefined, but at least
the gccgo runtime does this)