From mboxrd@z Thu Jan 1 00:00:00 1970 From: mzoran@crowfest.net (Michael Zoran) Date: Mon, 30 Jan 2017 10:34:59 -0800 Subject: ARM64: Disabling warnings about deprecated armv8 instructions In-Reply-To: References: <1485072424.14066.2.camel@crowfest.net> <1485075528.14345.1.camel@crowfest.net> <22169925.OhJ0QcnbHM@localhost> <1485087662.1518.1.camel@crowfest.net> <0D1F678D-6F94-4B68-955E-6454F8647FCA@linaro.org> <20170130141308.GV27312@n2100.armlinux.org.uk> <20170130165837.GE27312@n2100.armlinux.org.uk> <1485798092.484.5.camel@crowfest.net> Message-ID: <1485801299.1085.0.camel@crowfest.net> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Mon, 2017-01-30 at 18:17 +0000, M?ns Rullg?rd wrote: > Michael Zoran writes: > > > On Mon, 2017-01-30 at 17:09 +0000, Ard Biesheuvel wrote: > > > Well, the question is really how to deal with 32-bit > > > compatibility > > > given the fact that the ARM architecture will drop such > > > instructions > > > in its next revision. Whether we agree with that, and whether we > > > should argue our positions with the architects if we don't is not > > > relevant here. > > > > > > What is relevant is whether we inform userspace if we spot such a > > > deprecated instruction, and I think we should. > > > > > > Note that this is not only an issue for the arm64 kernel. The 32- > > > bit > > > kernel will have the exact same issue when you try to run it on > > > hardware that no longer has support for those instructions. > > > > Just to inject two cents worth since I'm still on the thread and I > > originally started the topic... > > > > The Intel comparison seems relevant.? I think in theory you can > > still > > run old MS-DOS software on an Intel PC if you were so inclined to > > do > > so. > > > > I would think the best would be to turn the warnings off by default > > when running in 32 bit mode with the option to turn them back on.? > > Then > > as time progresses more of more of these instructions can be > > converted > > to software emulation and removed from the hardware.? And hopefully > > as > > time progresses, all the user mode software gets upgraded to 64 bit > > so > > that 32 bit get dropped. > > > > The issue seems to me to be more that the kernel is screaming in > > the > > logs rather then if it's emulating the instructions in hardware or > > software. > > Might warning once be an acceptable compromise? Absolutely!