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Date: Thu, 5 Aug 2021 17:26:46 +0000
From: Joseph Myers <joseph@codesourcery.com>
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To: "H.J. Lu" <hjl.tools@gmail.com>
CC: <libc-alpha@sourceware.org>, Florian Weimer <fweimer@redhat.com>, Szabolcs
 Nagy <szabolcs.nagy@arm.com>, "Kirill A . Shutemov"
 <kirill.shutemov@linux.intel.com>
Subject: Re: [PATCH v5 1/1] <sys/tagged-address.h>: An API for tagged address
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On Thu, 5 Aug 2021, H.J. Lu via Libc-alpha wrote:

> +#ifdef __GNUC__
> +# if defined __USE_ISOC11 || defined __USE_ISOCXX11
> +#  ifdef __USE_ISOCXX11
> +#   define TAGGED_ADDRESS_ASSERT static_assert
> +#  else
> +#   define TAGGED_ADDRESS_ASSERT _Static_assert
> +#  endif

These __USE_* conditionals say what library features to enable.  
__USE_ISOC11 doesn't imply that C11 language features are available; you 
can use -D_ISOC11_SOURCE with a GCC version too old to support 
_Static_assert.

However, you should be able to rely on _Static_assert when building as C 
(regardless of feature test macros or compiler versions) because of the 
definition in sys/cdefs.h.

-- 
Joseph S. Myers
joseph@codesourcery.com