linux-kernel - Re: [PATCH] cgroup: reorder flexible array members of struct cgroup

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Date:   Sun, 22 Oct 2017 02:59:33 +1100
From:   Aleksa Sarai <asarai@...e.de>
To:     Tejun Heo <tj@...nel.org>,
        Nick Desaulniers <nick.desaulniers@...il.com>
Cc:     Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>, cgroups@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        Michael Davidson <md@...gle.com>,
        Greg Hackmann <ghackmann@...gle.com>, android-llvm@...gle.com
Subject: Re: [PATCH] cgroup: reorder flexible array members of struct
 cgroup_root

> Here, not necessarily but I don't want to move it for a bogus reason.
> Why would we disallow embedding structs with flexible members in the
> middle when it can be done and is useful?  If we want to discuss
> whether we want to avoid such usages in the kernel (but why?), sure,
> let's have that discussion but we can't decide that on "clang warns on
> it by default".

There was a talk a few years ago by the clang folks[1] saying that while 
trying to build a kernel with clang, they discovered that several places 
in the kernel uses "VLAIS" (variable Length Arrays In Structs") and 
argued that this is a violation of the C specification, despite it being 
a GNU extension. They also submitted several patches that removed this 
code (even working around a user-space visible usage of VLAIS).

[1]: 
https://www.linuxplumbersconf.org/2013/ocw/system/presentations/1221/original/VLAIS.pdf

-- 
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
https://www.cyphar.com/