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>
index | next in thread | previous in thread | raw e-mail
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:
>>
>>> 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.
>>
>> Correct.
>>
>> The pig in trying to build u-boot 2004.04 with Clang/XDEV is the use of
>>
>> #define DECLARE_GLOBAL_DATA_PTR register volatile gd_t *gd asm ("r9”)
>>
>> which means “gd is an alias for the r9 register and is a pointer to type …”
>>
>> … I think. :-)
>>
>> Clang doesn’t like this one bit. First objection is to “global register variables”, so if I experimentally knock out the “register”, I simply get the second objection - to "multiple instances of the r9 global variable”.
>>
>> Googling a bit suggests that Clang just plain can’t do this. :-(
>>
>> M
>
> 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.
what’s 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
home |
help
Want to link to this message? Use this
URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?7196A020-54E1-42FA-B8A0-25B145B0E412>