linux-kernel - Re: [PATCH] genksyms: Ignore module scoped _Static

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Date:   Tue, 1 Dec 2020 18:04:21 +0100
From:   Marco Elver <elver@...gle.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
        masahiroy@...nel.org, ndesaulniers@...gle.com, joe@...ches.com
Subject: Re: [PATCH] genksyms: Ignore module scoped _Static_assert()

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