Re: [PATCH v2] Remove the CONFIG_PRAGMA_DIAGNOSTIC_AVAILABLE switch

[Thomas Huth]

On 10/07/2020 15.25, Peter Maydell wrote:
> On Fri, 10 Jul 2020 at 05:56, Thomas Huth <thuth@redhat.com> wrote:
>>
>> GCC supports "#pragma GCC diagnostic" since version 4.6, and
>> Clang seems to support it, too, since its early versions 3.x.
>> That means that our minimum required compiler versions all support
>> this pragma already and we can remove the test from configure and
>> all the related #ifdefs in the code.
>>
>> Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
>> Signed-off-by: Thomas Huth <thuth@redhat.com>
>> ---
>>  v2: Keep the !defined(__clang__) in coroutine-ucontext.c
> 
> If we're going to mandate "at least gcc 4.6 or clang", perhaps
> we should have a sanity check for it, something like
> 
> #if !defined __clang__
> # if !QEMU_GNUC_PREREQ(4, 6)
> #  error QEMU requires at least GCC 4.6
> # endif
> #endif
> 
> (maybe also check clang version, though that is more awkward
> because upstream clang and Apple's compiler set the version
> number defines differently.)
> 
> We could put that in compiler.h. Checking in configure would be
> more userfriendly but maybe a little more effort.
> The other advantage of this check is we have effectively
> some internal documentation of our current minimum
> compiler requirement.

It's already there. Look for:

 "You need at least GCC v4.8 or Clang v3.4 (or XCode Clang v5.1)"

in the configure script.

> There is also some tidying up that can then be done:
> several places in the code use QEMU_GNU_PREREQ() to insist
> on "at least gcc 4.4" or "at least gcc 4.6",
Oh, weird, I thought we got rid of all of them when we bumped the
minimum requirement to GCC 4.8 ... these spots could certainly be
cleaned up nowadays.

 Thomas