Re: [Xen-devel] [PATCH XTF 1/4] build: Support BUILD_BUG_ON() with compilers lacking _Static_assert()

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 28.09.17 at 14:34, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 28/09/17 13:32, Jan Beulich wrote:
>>>>> On 28.09.17 at 12:59, <andrew.cooper3@xxxxxxxxxx> wrote:
>>> --- /dev/null
>>> +++ b/include/xtf/compiler-gcc.h
>>> @@ -0,0 +1,31 @@
>>> +#ifndef XTF_COMPILER_GCC_H
>>> +#define XTF_COMPILER_GCC_H
>>> +
>>> +#define GCC_VER (__GNUC__ * 10000 +                \
>>> +            __GNUC_MINOR__ * 100 +         \
>>> +            __GNUC_PATCHLEVEL__)
>>> +
>>> +/*
>>> + * The Clang __has_*() infrastructure is a very clean way to identify
>>> + * compiler support, without resorting to version checks.  Fake up
>>> + * enough support for XTF code to use, even on non-clang compilers.
>>> + */
>>> +
>>> +#ifndef __has_extension
>>> +
>>> +#define GCC_HAS_c_static_assert (GCC_VER >= 40600) /* _Static_assert() */
>>> +
>>> +#define __has_extension(x) GCC_HAS_ ## x
>> As always I'd recommend against underscore prefixed names.
> 
> In this case, its a Clang feature which I'm deliberately trying to use.
> 
> https://clang.llvm.org/docs/LanguageExtensions.html#feature-checking-macros 

Oh, sorry, should have paid closer attention to the comment.
But wouldn't it still be better to define has_extension(), simply
evaluating to _has_extension() for clang?

Jan


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