Date: Thu, 12 Feb 2015 16:11:29 -0700 From: Warner Losh <imp@bsdimp.com> To: Andrew Turner <andrew@fubar.geek.nz> Cc: freebsd-arm@freebsd.org Subject: Re: FreeBSD/arm64 MACHINE/MACHINE_ARCH identification Message-ID: <51DBDD85-A1FD-4A18-946D-FB78252BB845@bsdimp.com> In-Reply-To: <20150212225655.26c865aa@bender.lan> References: <CAPyFy2A=Ev5gdYPKgEE0LS3-1sY%2BXmkZA7VCe71E6Fmbb=vMRw@mail.gmail.com> <607BF592-A09B-4DB4-9872-C9E63066AB57@bsdimp.com> <CAPyFy2Bgrap3TkFNuChyMC0Vwbjdt5FVW0ey03XtkK1iwNL1KQ@mail.gmail.com> <71E9C1B9-F819-420B-90A5-A36D58E71817@bsdimp.com> <CAPyFy2ATn5xgsvePCdvzqnyBS45izVHdL8yLaQQoKeJenSv9tg@mail.gmail.com> <228428CC-4042-4902-90A4-E7040F4BFFF5@bsdimp.com> <CAPyFy2BKzhiA4tbi-mXd6T114_zawmWTi3XbyXiUcgijQfHdyw@mail.gmail.com> <54DCE9B5.8040203@freebsd.org> <EC5AAE72-F553-4F31-8768-9854B6EE2C69@bsdimp.com> <20150212225655.26c865aa@bender.lan>
next in thread | previous in thread | raw e-mail | index | archive | help
> On Feb 12, 2015, at 3:56 PM, Andrew Turner <andrew@fubar.geek.nz> = wrote: >=20 > On Thu, 12 Feb 2015 11:37:38 -0700 > Warner Losh <imp@bsdimp.com> wrote: >=20 >>=20 >>> On Feb 12, 2015, at 10:58 AM, Nathan Whitehorn >>> <nwhitehorn@freebsd.org> wrote: >>>=20 >>> On 02/12/15 09:15, Ed Maste wrote: >>>>>> Oh - I don't care what directory Linux puts the kernel source >>>>>> in, only what's reported by uname. As far as I can tell that >>>>>> has always been aarch64 for uname -m. >>>>>=20 >>>>> Traditionally in Linux, they have been a matched set. >>>>=20 >>>> Ok, it appears they may have abandoned this. >>>>=20 >>>>>> We might decide that "uname -m" has to be aarch64 to match >>>>>> expectations of third-party software set by other operating >>>>>> systems. If that in turn means we have to move the kernel >>>>>> source, so be it. >>>>>=20 >>>>> This one I=E2=80=99m not on board with. You=E2=80=99ve not made a = compelling case >>>>> for it yet. >>>>=20 >>>> That's why I said "we might decide" -- I'm not sure myself. >>>>=20 >>>> However, there's no backwards compatibility concern here, we've >>>> never had a FreeBSD release that reports "arm64" for "uname -m". >>>> There's no reason for us to prefer "arm64" if everyone else uses >>>> "aarch64." Also, having arm64 for uname -m and aarch64 for uname >>>> -p seems a bit odd. >>>=20 >>> I would assume uname -m would be "arm", not "arm64". Unless there >>> are fundamental platform differences you are baking in somehow, >>> which I don't know. >>=20 >> arm would be a pleasing outcome, but looking at his WIP tree, it >> looks like it would be possible, but rather inconvenient to merge the >> arm64 bits back under arm and make them conditional. >=20 > They are two different architectures. They don't share any assembly, > and the exception handling is different, both in exception types and > number of modes/levels. >=20 > Along with this they only sort of share the special registers. The > method to access them is different, on 32-bit it is via a coprocessor > call where on 64-bit there is an instruction to get them by name. >=20 > We may be able to share some of the new pmap code, however it would > need a lot of work as the virtual memory layout is different and it is > likely we will need to handle 64k granules on arm64 in the future. > Because of this any sharing there would need to be handled carefully. >=20 > The interrupt controller and timer drivers will be shared, but these > are both devices and maybe they should be moved under sys/dev. Yea, rather inconvenient :) > The two architectures will share very little code or headers. An ARMv8 > core may be able to execute either 32 or 64-bit code (both are = optional > so either one or both options will be enabled) so there is a case for > use to handle cc -m32, but I don't feel this is enough justification = to > merge two otherwise different architectures just because they were > designed by the same company. We support -m32 on x86 where we have amd64 and i386 MACHINE values and directories today. I=E2=80=99m not sure how having either = aarch64/aarch64 or arm64/aarch64 instead of arm/aarch64 would preclude -m32 from working. Warner
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?51DBDD85-A1FD-4A18-946D-FB78252BB845>