Re: [Qemu-devel] [PATCH for-4.0] compiler.h: Add an explicit check for the compiler version

["Daniel P. Berrangé" <berrange@redhat.com>]

On Fri, Nov 30, 2018 at 11:43:40AM +0100, Thomas Huth wrote:
> The questions about our minimum compiler requirement pops up every
> couple of months, and we then have to recall the details each time.
> So let's document this in a proper way, by adding a comment and
> check for the right compiler version to our compiler.h header.
> 
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>  include/qemu/compiler.h | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/include/qemu/compiler.h b/include/qemu/compiler.h
> index ca9bc85..775446b 100644
> --- a/include/qemu/compiler.h
> +++ b/include/qemu/compiler.h
> @@ -22,6 +22,14 @@
>  # define QEMU_GNUC_PREREQ(maj, min) 0
>  #endif
>  
> +/*
> + * We need at least GCC 4.1 for atomics support. Clang also supports these,
> + * and reports itself as GCC 4.2, so it passes this check, too.
> + */
> +#if !QEMU_GNUC_PREREQ(4, 1)
> +#error QEMU needs a compiler that is compatible with GCC v4.1 or newer
> +#endif

This encodes our current minimum which is fine as a first step.

I think we could reasonably increase our min version now that we
have declared explicitly what platforms we intend to support

      RHEL-7: 4.8.5
      Debian (Stretch): 6.3.0
      Debian (Jessie): 4.8.4
      OpenBSD (ports): 4.9.4
      FreeBSD (ports): 8.2.0
      OpenSUSE Leap 15: 7.3.1
      Ubuntu (Xenial): 5.3.1
      macOS (Homebrew): 8.2.0

Arguably we don't care about gcc version for *BSD and macOS since those
platforms normally use CLang

Anyway, with this info I think we can reasonably pick gcc 4.8.0

We would need an explicit check for clang, however, instead of
relying on it claiming gcc 4.2 support - that's a way inaccurate
claim anyway so detecting a specific clang version would be
better regardless IMHO


Regards,
Daniel
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