linux-kernel - Re: [PATCH linux-next] Documentation: Build mic/mpssd only for x86

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Date:	Fri, 5 Dec 2014 14:53:40 -0500
From:	Dan Streetman <ddstreet@...e.org>
To:	Ashutosh Dixit <ashutosh.dixit@...el.com>
Cc:	Jonathan Corbet <corbet@....net>, Jiri Kosina <jkosina@...e.cz>,
	Peter Foley <pefoley2@...oley.com>,
	Randy Dunlap <rdunlap@...radead.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jennings <sjennings@...iantweb.net>,
	"Yokoyama, Caz" <caz.yokoyama@...el.com>,
	"Dutt, Sudeep" <sudeep.dutt@...el.com>,
	"Chandramouli, Dasaratharaman" 
	<dasaratharaman.chandramouli@...el.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"Rao, Nikhil" <nikhil.rao@...el.com>,
	Daniel Borkmann <dborkman@...hat.com>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	Siva Yerramreddy <yshivakrishna@...il.com>
Subject: Re: [PATCH linux-next] Documentation: Build mic/mpssd only for x86_64

On Fri, Dec 5, 2014 at 1:18 PM, Ashutosh Dixit <ashutosh.dixit@...el.com> wrote:
> On Thu, Dec 04 2014 at 07:27:06 PM, Dan Streetman <ddstreet@...e.org> wrote:
>> On Thu, Dec 4, 2014 at 4:27 PM, Ashutosh Dixit <ashutosh.dixit@...el.com> wrote:
>>> mic/mpssd along with MIC drivers are currently only usable on
>>> x86_64. So build mic/mpssd only for x86_64 to avoid build breaks on
>>> big-endian systems.
>>
>> Only building for x86_64 is fine, but in that case what's the point of
>> leaving the htole16() et. al. functions in mpssd.c?  Shouldn't they be
>> removed?
>
> I am hoping that once glibc is fixed we can remove this limitation on
> building only for x86_64, so I'd rather htole16() et. al. stayed.

FYI, the bug I opened with glibc:
https://sourceware.org/bugzilla/show_bug.cgi?id=17679

was rejected because Andreas states "C does not allow function calls
in file scope."  The suggestion was made to try to fix gcc, but
honestly I don't have the time (or energy) to push for a gcc change
just for this. :-)

I do think it's too bad that glibc hto* functions don't work in file
scope (i.e. with static/global var initialization) for constant values
(using them with variables is different, which is why
__bswap_constant_* works in file scope but __bswap_* doesn't), since
it's simply a 2-step process that's entirely doable by the
preprocessor and/or compiler; just check if target endianness matches
desired endianness, and if not the compiler does a simple byte swap of
the constant value.

Anyway, I doubt glibc and/or gcc will be updated anytime soon to allow this.

>  As I
> said earlier, I'm fine with your patch too, but restricting the build
> for x86_64 seems to be the smallest patch which provides an acceptable
> solution.

Fine with me too.  It'll get big-endian building again.
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