Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH] genksyms: Ignore module scoped _Static_assert()
To:     Nick Desaulniers <ndesaulniers@google.com>,
        Marco Elver <elver@google.com>
Cc:     Christoph Hellwig <hch@infradead.org>,
        LKML <linux-kernel@vger.kernel.org>,
        kasan-dev <kasan-dev@googlegroups.com>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Joe Perches <joe@perches.com>, George Burgess <gbiv@google.com>
References: <20201201152017.3576951-1-elver@google.com>
 <20201201161414.GA10881@infradead.org>
 <20201201170421.GA3609680@elver.google.com>
 <CAKwvOdkhBTjjtEm9dc9irp8hpWoEDEAMj_Zp4ntKspgDkjrATg@mail.gmail.com>
From:   Rasmus Villemoes <linux@rasmusvillemoes.dk>
Message-ID: <764b18d4-b519-9f27-f66b-7cfdab61b313@rasmusvillemoes.dk>
Date:   Tue, 1 Dec 2020 22:01:36 +0100
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.10.0
MIME-Version: 1.0
In-Reply-To: <CAKwvOdkhBTjjtEm9dc9irp8hpWoEDEAMj_Zp4ntKspgDkjrATg@mail.gmail.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 01/12/2020 20.56, Nick Desaulniers wrote:
> On Tue, Dec 1, 2020 at 9:04 AM Marco Elver <elver@google.com> wrote:
>>
>> 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?
>>
> And to proactively address the inevitable: why do we have both?  We
> looked into wholesale replacing BUILD_BUG_ON's implementation with
> _Static_assert, but found that they differ slightly in the handling of
> integer constant expressions; BUILD_BUG_ON was reliant on some
> compiler optimizations in expressions making use of
> __builtin_constant_p that cannot be evaluated when the compiler
> performs the _Static_assert check. 

... and _Static_assert() is a declaration, so even many of the
BUILD_BUG_ON() that have a bona fide ICE cannot be converted because
declaration-after-statement.

Rasmus