From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave.Martin@arm.com (Dave Martin) Date: Mon, 5 Dec 2016 15:04:55 +0000 Subject: [RFC PATCH 00/29] arm64: Scalable Vector Extension core support In-Reply-To: <0293f7d3-b3d3-1a68-5b99-75db195eb796@redhat.com> References: <20161130120654.GJ1574@e103592.cambridge.arm.com> <3e8afc5a-1ba9-6369-462b-4f5a707d8b8a@redhat.com> <20161130135631.GK1574@e103592.cambridge.arm.com> <20161201103048.GO1574@e103592.cambridge.arm.com> <0293f7d3-b3d3-1a68-5b99-75db195eb796@redhat.com> Message-ID: <20161205150452.GT1574@e103592.cambridge.arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Mon, Dec 05, 2016 at 11:44:38AM +0100, Florian Weimer wrote: > On 12/01/2016 11:30 AM, Dave Martin wrote: > > >>The VL value is implicitly thread-local data, and the encoded state may have > >>an implicit dependency on it, although it does not contain vector registers > >>as such. > > > >This doesn't sound like an absolute requirement to me. > > > >If we presume that the SVE registers never need to get saved or > >restored, what stops the context data format being VL-independent? > > I'm concerned the suspended computation has code which has been selected to > fit a particular VL value. > > > If the save/restore logic doesn't touch SVE, which would its > > implementation be VL-dependent? > > Because it has been optimized for a certain vector length? I'll respond to these via Szabolcs' reply. > >>>Because the SVE procedure call standard determines that the SVE > >>>registers are caller-save, > >> > >>By the way, how is this implemented? Some of them overlap existing > >>callee-saved registers. > > > >Basically, all the *new* state is caller-save. > > > >The Neon/FPSIMD regs V8-V15 are callee-save, so in the SVE view > >Zn[bits 127:0] is callee-save for all n = 8..15. > > Are the extension parts of registers v8 to v15 used for argument passing? No -- the idea is to be directly compatible with the existing PCS. > If not, we should be able to use the existing dynamic linker trampoline. Yes, I believe so. Cheers ---Dave