Date: Thu, 28 Jun 2012 16:31:36 -0600 From: Warner Losh <wlosh@bsdimp.com> To: Ian Lepore <freebsd@damnhippie.dyndns.org> Cc: arm@freebsd.org Subject: Re: Naming mess... Message-ID: <3AB368CC-BE8B-4058-A342-763B8C073800@bsdimp.com> In-Reply-To: <1340921715.1110.100.camel@revolution.hippie.lan> References: <FB2E340B-34DD-4CBC-B539-6996E79F37E3@freebsd.org> <1340921715.1110.100.camel@revolution.hippie.lan>
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On Jun 28, 2012, at 4:15 PM, Ian Lepore wrote:
> On Tue, 2012-06-26 at 22:21 -0700, Tim Kientzle wrote:
>> I've been building on Warner's ARMv6 cleanup patches and
>> have them almost ready to commit to the armv6 tree (including
>> the necessary configuration glue for GCC to actually default
>> properly).
>>=20
>> In the process, I've uncovered the following confusing bit of naming:
>>=20
>> __ARM_ARCH_6__
>> _ARM_ARCH_6
>> ARM_ARCH_6
>>=20
>> The above are three symbols defined in different parts
>> of the code with entirely different meanings. The
>> pattern extends in the obvious way.
>>=20
>> After some tracing, I figured out what they mean today:
>>=20
>> __ARM_ARCH_6__ is defined by GCC if it is currently targeting a =
processor that is exactly ARMv6. Two such symbols are never defined at =
the same time. The patches I'm working on arrange for this to be =
properly set in the armv6 builds.[0]
>>=20
>> _ARM_ARCH_6 is defined in asm.h (and has been redefined elsewhere, =
but I'm removing those) to indicate that the currently targeted =
processor is _at_least_ ARMv6. Several such macros can be defined at =
the same time. These are more useful in practice than the GCC symbols. =
Unfortunately, besides the poor naming, defining these symbols in asm.h =
means they cannot be used in C code.
>>=20
>> ARM_ARCH_6 is used within the kernel source to indicate that support =
routines should be included for this class of processor. Multiple such =
symbols can be defined at the same time if you're building a kernel with =
support for multiple CPUs.
>>=20
>> Here's what I would like to do:
>>=20
>> * The first is a given and we should leave it alone. The patches =
I'm cleaning up make this useful in the armv6 tree.
>>=20
>> * The second I would like to move out of asm.h so it can be used in =
C code. I would like to rename it to _HAVE_ARMv6_INSTRUCTIONS, which I =
think is clearer. I have renamed it in my patches but not yet moved it =
to another header. Suggestions appreciated.
>>=20
>> "NEED_ARM_ARCH_6_SUPPORT" * Someday, I would like to rename the third =
one, though I don't have a concrete proposal yet. =
("NEED_ARM_ARCH_6_SUPPORT" is expressive but wordy; better suggestions =
appreciated.)
>>=20
>> Cheers,
>>=20
>> Tim
>>=20
>> [0] This page has a nice table: =
https://wiki.edubuntu.org/ARM/Thumb2PortingHowto
>>=20
>=20
> I'm not working with armv6 stuff yet, but I like all of what you
> propose. I can't help but note that NEED_ARM_ARCH_6_SUPPORT is =
actually
> shorter than _HAVE_ARMv6_INSTRUCTIONS. If it's just too wordy, maybe
> the "NEED_" part could be left off. =20
#define ARM_ARCH 6
#if ARM_ARCH >=3D 6
...
#endif
Might not be the worst idea...
Warner=
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