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Date:   Tue, 1 Dec 2020 18:04:21 +0100
From:   Marco Elver <elver@google.com>
To:     Christoph Hellwig <hch@infradead.org>
Cc:     linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com,
        masahiroy@kernel.org, ndesaulniers@google.com, joe@perches.com
Subject: Re: [PATCH] genksyms: Ignore module scoped _Static_assert()
Message-ID: <20201201170421.GA3609680@elver.google.com>
References: <20201201152017.3576951-1-elver@google.com>
 <20201201161414.GA10881@infradead.org>
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On Tue, Dec 01, 2020 at 04:14PM +0000, Christoph Hellwig wrote:
> Why not use the kernels own BUILD_BUG_ON instead of this idiom?

BUILD_BUG_ON() was conceived before there was builtin compiler-support
in the form of _Static_assert() (static_assert()), which has several
advantages (compile-time performance, optional message) but most
importantly, that it can be used at module/global scope (which
BUILD_BUG_ON() cannot).

From include/linux/build_bug:

	/**
	 * static_assert - check integer constant expression at build time
	 *
	 [...]
	 *
	 * Contrary to BUILD_BUG_ON(), static_assert() can be used at global
	 * scope, but requires the expression to be an integer constant
	 * expression (i.e., it is not enough that __builtin_constant_p() is
	 * true for expr).
	 [...]

.. and there are plenty of global/module scoped users of it already.

Thanks,
-- Marco