Date: Mon, 12 Jun 2017 13:07:15 -0700 From: Russell Haley <russ.haley@gmail.com> To: Mark Millard <markmi@dsl-only.net> Cc: Warner Losh <imp@bsdimp.com>, "freebsd-arm@freebsd.org" <freebsd-arm@freebsd.org> Subject: Re: Creating armv7 MACHINE_ARCH Message-ID: <CABx9NuRBQbXO70t7UH7bLc5Xs5e_qm09Uwh628i272y9tfb_PQ@mail.gmail.com> In-Reply-To: <2A90A527-7DCA-4442-9322-0EA96236583C@dsl-only.net> References: <CANCZdfpUjPBRpxpmjtwK-wpiK=%2BwHscS4UmVeatrE7vrm260tw@mail.gmail.com> <20170612152808.6094931.74364.27128@gmail.com> <CANCZdfrxTo8vLsnjU_VerO%2B3%2BU=06cok7%2BuKba3FM8_nXFozhQ@mail.gmail.com> <B19EDB95-2A23-4F8F-8414-3F4E0E65AC4B@dsl-only.net> <CABx9NuQTOkf6HK=RacUCBR=W_WDfgZwbVHYwsRdx0YJd=zr51w@mail.gmail.com> <2A90A527-7DCA-4442-9322-0EA96236583C@dsl-only.net>
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On Mon, Jun 12, 2017 at 1:00 PM, Mark Millard <markmi@dsl-only.net> wrote: > On 2017-Jun-12, at 12:16 PM, Russell Haley <russ.haley@gmail.com> wrote: > >> On Mon, Jun 12, 2017 at 10:36 AM, Mark Millard <markmi@dsl-only.net> wrote: >>> >>> On 2017-Jun-12, at 8:39 AM, Warner Losh <imp at bsdimp.com> wrote: >>> >>>> . . . >>>> >>>> Plus, we aren't quite doing what Ian wanted. He wanted a full rename. The >>>> proposal on the able is to add an armv7 TARGET_ARCH in 12. Not to rename or >>>> remove armv6. Sadly, that will still be there since the RPI foundation >>>> keeps finding new ways to repackage the rpi into new boards that are just >>>> too cheap to ignore. >>> >>> On 2017-Jun-12, at 6:59 AM, Andrew Turner <andrew@fubar.geek.nz> wrote: >>> >>>> I like this. My understanding is adding armv7 would also fix many of the currently broken ports that assume they are being built for armv7 as many Linux distros target ARMv7+. >>>> >>>> It should also be noted the GENERIC kernel is likely to only ever target ARMv7+ even without an armv7 TARGET_ARCH. >>> >>> >>> Hopefully the choices related to TARGET and TARGET_ARCH >>> for armv7 end up identifying the context to port builds >>> so that many would just automatically do the right thing. >>> >>> >>> As for GENERIC: >>> >>> powerpc has. . . >>> >>> TARGET=powerpc TARGET_ARCH=powerpc and GENERIC >>> TARGET=powerpc TARGET_ARCH=powerpc64 and GENERIC64 >>> >>> So there is precedent for more than one GENERIC* >>> for a family, with which one being appropriate >>> being based on TARGET_ARCH. >>> >>> For powerpc TARGET=powerpc implicitly uses >>> TARGET_ARCH=powerpc when TARGET_ARCH is not >>> specified (if I remember right). Which should >>> be the default for armv6 vs. armv7 might go >>> the other direction (TARGET_ARCH=armv7 by >>> default). >>> >>> >>> Side note: >>> >>> A caution about talking about "rpi2" as >>> an example. . . >>> >>> Raspberry Pi 2 Model B V1.2 is Cortex-A53 based >>> (so arm64/aarch64). (A BCM2837, not a BCM2836.) >>> This dates about to something like 2014 based >>> on the pictures showing the (c) notice on the >>> boards. >>> >>> V1.1 and before were armv7 (BCM2836) based. >>> >>> Unless a kernel and world are made that can >>> also configure/handle a Cortex-A53 in a >>> armv7-like manor there will be two different >>> GENERIC builds in order to span the "rpi2" >>> family, based on just V1.2+ vs. V1.1 and >>> before. >>> >>> (A single, modern distribution of the official >>> Raspbian software for the rpi2 does support >>> all the V1.x boards if I understand right.) >> >> I am confused. I don't see any documentation about Raspbian supporting 64 bit? > > 64-bit Cortex-A53's can be configure to operate in a > 32-bit mode (AArch32). Raspian does that for RPI2 V1.2 > and for RPI3. > > Raspian does not (yet?) support a 64-bit mode (AArch64). > > The Cortex-A53 can support either. As I understand it > is possible for an OS to allow a user processes to be > one or the other, different processes using the different > modes. That does not mean that all operating systems > bother to. > > If I remember right the official Ubuntu for an ODroid-C2 > allows both AArch64 and AArch32 user programs (and > so processes, with shared library types tracking). > >> From Arm at https://www.arm.com/products/processors/cortex-a/cortex-a53-processor.php: >> "The Cortex-A53 supports the full ARMv8-A architecture. It not only >> runs 64-bit applications also seamlessly and efficiently runs legacy >> ARM 32-bit applications." >> >> I assume that means it handles armv7-A without issue? (In fact, many >> on this board know it does) > > I've not gone through the details but targeting AArch32 > probably means targeting a subset of armv7. Or may be > to support both requires targeting a common subset of both. > (My guess is that AArch32 is the definition of a common > subset for 32-bit, at least for user processes.) > > Raspian targets just AArch32 on armv7 and Cortex-A53 > (user space). (If I've got the definition of AArch32 > right: otherwise a common subset.) > > FreeBSD targets armv7 and AArch64 separately (via > separate GENERIC kernels). I'm not aware of FreeBSD > targeting AArch32 at all on cores capable of AArch64. > FreeBSD possibly does not restrict itself to AArch32 > (user processes) on armv7 if AArch32 is really a > subset. I thought all 64 bit Arm instructions are defined in armv8? Russ
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