Date: Thu, 17 Apr 2014 13:14:25 -0600 From: Warner Losh <imp@bsdimp.com> To: Ian Lepore <ian@FreeBSD.org> Cc: Tim Kientzle <tim@kientzle.com>, freebsd-arm <freebsd-arm@FreeBSD.org>, ticso@cicely.de, Mark R V Murray <mark@grondar.org> Subject: Re: Building an ARM/RPI-B release (hacked) on CURRENT/AMD64. Message-ID: <7196A020-54E1-42FA-B8A0-25B145B0E412@bsdimp.com> In-Reply-To: <1397761628.1124.245.camel@revolution.hippie.lan> References: <9FDD6F0E-B2A9-48D9-A3E4-181868995FDA@grondar.org> <EC41E53F-96EF-4652-9A02-D49448D104BE@kientzle.com> <20140417103117.GE44138@cicely7.cicely.de> <1397738961.1124.157.camel@revolution.hippie.lan> <ED243420-AC33-4D90-A23D-0266C142F3C1@grondar.org> <1397761628.1124.245.camel@revolution.hippie.lan>
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On Apr 17, 2014, at 1:07 PM, Ian Lepore <ian@FreeBSD.org> wrote:
> On Thu, 2014-04-17 at 19:01 +0100, Mark R V Murray wrote:
>> On 17 Apr 2014, at 13:49, Ian Lepore <ian@FreeBSD.org> wrote:
>>=20
>>> U-boot requires that a global register be set aside by the compiler =
and
>>> it's used to access all global vars. As I vaguely understand it, =
u-boot
>>> used to want r8 for this, and clang didn't used to support the =
concept
>>> at all. Now clang supports it, but only for r9, and apparently more
>>> recent u-boot expects r9 rather than r8. So the fix is probably to =
use
>>> more recent u-boot sources (I've been using 2014.01 for imx6 stuff), =
and
>>> probably to add the new -ffixed-r9 flag for a clang build.
>>=20
>> Correct.
>>=20
>> The pig in trying to build u-boot 2004.04 with Clang/XDEV is the use =
of
>>=20
>> #define DECLARE_GLOBAL_DATA_PTR register volatile gd_t =
*gd asm ("r9=94)
>>=20
>> which means =93gd is an alias for the r9 register and is a pointer to =
type =85=94
>>=20
>> =85 I think. :-)
>>=20
>> Clang doesn=92t like this one bit. First objection is to =93global =
register variables=94, so if I experimentally knock out the =93register=94=
, I simply get the second objection - to "multiple instances of the r9 =
global variable=94.
>>=20
>> Googling a bit suggests that Clang just plain can=92t do this. :-(
>>=20
>> M
>=20
> Hmmm. After a bit of poking around in the llvm code, it looks like =
the
> full extent of the support for -ffixed-r9 is that it doesn't consider
> that register available for use by the code generator; that's only =
part
> of what u-boot needs. =20
what=92s the other part? Global register variables like this?
> Some online notes I found for clang 3.5 claim that global register
> variables aren't supported, and aren't likely to be any time soon.
Is that a poke in the eye of uboot, or is it more of a contention that
uboot is moving away from that need?
Warner
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