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

[Julien Grall <julien.grall@xxxxxxx>]

Hi,

On 28/03/2019 10:56, Jan Beulich wrote:
> > > > On 28.03.19 at 11:43, <andrew.cooper3@xxxxxxxxxx> wrote:
> > On 28/03/2019 10:28, Jan Beulich wrote:
> > > > > > On 28.03.19 at 11:14, <andrew.cooper3@xxxxxxxxxx> wrote:
> > > > 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.
> > > Are you sure a distro caring about, say, only x86 would indeed
> > > enable Arm and all sorts of other architectures in the compiler,
> > > just because it can be enabled? IOW I assume the need for an
> > > override to the system default clang binaries would still exist.
> > I've just tried, and Ubuntu 16.04's default clang-3.8 is perfectly happy
> > compiling Aarch64, and makes a suitable looking elf object.  (I can't
> > actually disassemble it because objdump chokes, but .text is the
> > expected length)
> >
> > As the cross-compilation documentation states, this is a deliberate
> > design decision which, amongst other things, prevents distros from
> > needing to maintain per-arch packages.
> All understood, just that Ubuntu may not be a good example, as
> there looks to be Ubuntu 16.04 for 64-bit Arm.
It occurs to me that other compiler may be based on clang/llvm but use a 
different name. For instance, the Arm Compiler is called armclang.
armclang only supports arm32 and arm64 and require to always pass the target 
triple using --target (Not the -- rather than -).
So we would need to cater different clang binary in the future.

Cheers,

--
Julien Grall

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