Re: [Qemu-devel] [PATCH for-1.7] target-i386: Fix build by providing stub kvm_arch_get_supported_cpuid()

[Anthony Liguori]

On Tue, Nov 12, 2013 at 8:08 AM, Peter Maydell <address@hidden> wrote:
> On 12 November 2013 15:58, Paolo Bonzini <address@hidden> wrote:
>> I don't really see a reason why QEMU should give clang more weight than
>> Windows or Mac OS X.
>
> I'm not asking for more weight (and actually my main
> reason for caring about clang is exactly MacOSX). I'm
> just asking that when a bug is reported whose underlying
> cause is "we don't work on clang because we're relying on
> undocumented behaviour of gcc" with an attached patch that
> fixes this by not relying on the undocumented behaviour,
> that we apply the patch rather than saying "why do we
> care about clang"...

QEMU has always been intimately tied to GCC.  Heck, it all started as
a giant GCC hack relying on entirely undocumented behavior (dyngen's
disassembly of functions).

There's nothing intrinsically bad about being tied to GCC.  If you
were making argument that we could do it a different way and the
result would be as nice or nicer, then it wouldn't be a discussion.

But if supporting clang means we have to remove useful things, then
it's always going to be an uphill battle.

In this case, the whole discussion is a bit silly.  Have you actually
tried -O1 under a debugger with clang?  Is it noticably worse than
-O0?

I find QEMU extremely difficult to use an interactive debugger on
anyway.  I doubt the difference between -O0 and -O1 is even close to
the breaking point between usability under a debugger...

Regards,

Anthony Liguori

> This seems to me to be a win-win situation:
>  * we improve our code by not relying on undocumented
>    implentation specifics
>  * we work on a platform that, while not a primary
>    platform, is at least supported in the codebase and
>    has people who fix it when it breaks
>
> -- PMM