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Re: [PATCH v2 1/7] xen: implement byteswap.h


  • To: Lin Liu <lin.liu@xxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Fri, 22 Oct 2021 15:00:57 +0100
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  • Cc: George Dunlap <george.dunlap@xxxxxxxxxx>, Ian Jackson <iwj@xxxxxxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>
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  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 22/10/2021 11:47, Lin Liu wrote:
> diff --git a/xen/include/xen/compiler.h b/xen/include/xen/compiler.h
> index 696c7eb89e..68f28082a5 100644
> --- a/xen/include/xen/compiler.h
> +++ b/xen/include/xen/compiler.h
> @@ -179,4 +179,16 @@
>  # define CLANG_DISABLE_WARN_GCC_COMPAT_END
>  #endif
>  
> +#if (!defined(__clang__) && (__GNUC__ < 10))

This too lost my feedback.

It needs to be #ifndef __has_builtin because otherwise a random GCC 10
build I have fails with:

/local/security/xen.git/xen/include/xen/byteswap.h:6:19: error: missing
binary operator before token "("
    6 | #if !__has_builtin(__builtin_bswap16)


I suspect it was a build of GCC 10 before __has_builtin() support was
added, but either way, we should be predicating on __has_builtin itself,
not version guesswork.

~Andrew




 


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