Re: [PATCH 01/12] xen: clang: Support correctly cross-compile

From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Jan Beulich <JBeulich@suse.com>, Julien Grall <julien.grall@arm.com>
Cc: Artem Mygaiev <artem_mygaiev@epam.com>,
	Stefano Stabellini <sstabellini@kernel.org>,
	"andrii_anisov@epam.com" <andrii_anisov@epam.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	George Dunlap <George.Dunlap@eu.citrix.com>,
	Tim Deegan <tim@xen.org>, Ian Jackson <Ian.Jackson@eu.citrix.com>,
	oleksandr_tyshchenko@epam.com,
	xen-devel <xen-devel@lists.xenproject.org>,
	Wei Liu <wei.liu2@citrix.com>
Subject: Re: [PATCH 01/12] xen: clang: Support correctly cross-compile
Date: Thu, 28 Mar 2019 10:14:27 +0000	[thread overview]
Message-ID: <22e51ded-0ca3-6832-dcc3-9849d782816c@citrix.com> (raw)
In-Reply-To: <5C9C9A22020000780022265A@prv1-mh.provo.novell.com>

On 28/03/2019 09:55, Jan Beulich wrote:
>>>> On 27.03.19 at 19:45, <julien.grall@arm.com> wrote:
>> Clang uses "-target" option for cross-compilation.
> And all possible targets are always available? I'd like to point out
> that CROSS_COMPILE can be used for other than actual cross
> compilation, e.g. building with just an alternative tool chain
> built for the same target. Dropping the $(CROSS_COMPILE)
> prefixes makes this impossible afaict. Requiring suitable wrapper
> scripts to be put in place would seem better to me.
>
> I also wonder why this change is needed for Arm, but wasn't
> needed so far for x86. But perhaps no-one ever tried using it
> so far ...

It seems that CROSS_COMPILE is a GNU-ism, which is not shared by the
clang world.  I can't find anything which will make you a
$FOO-$BAR-clang binary, whereas you do typically get clang-$X aliases
for the different versions of clang.

Using -target is from the Clang instructions on cross compilation, which
say to do it this way.  https://clang.llvm.org/docs/CrossCompilation.html

The targets supported will depend on the configuration Clang was
compiled with, but Clang specifically opposes GCC's way of requiring the
user to recompile for every different target.  It is expected that a
packager of clang will enable all of the supported targets in the
package they distribute.

~Andrew

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