From: Arnd Bergmann <arnd@arndb.de>
Subject: Re: [PATCH 1/2] ext4: fix warning about stack corruption
Date: Tue, 22 Aug 2017 13:57:12 +0200
Message-ID: <CAK8P3a05GOh87tGhnuUS_gYmQVjgTrC-e58KagVPG4hHSuFTgg@mail.gmail.com>
References: <20170726185219.GA57833@beast> <20170801120438.1582336-1-arnd@arndb.de>
 <20170822210849.0edb91cc@kryten>
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Cc: "Theodore Ts'o" <tytso@mit.edu>,
        Andreas Dilger <adilger.kernel@dilger.ca>,
        Kees Cook <keescook@chromium.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Jan Kara <jack@suse.cz>,
        Chandan Rajendra <chandan@linux.vnet.ibm.com>,
        linux-ext4@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
To: Anton Blanchard <anton@ozlabs.org>
Return-path: <linux-kernel-owner@vger.kernel.org>
In-Reply-To: <20170822210849.0edb91cc@kryten>
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List-Id: linux-ext4.vger.kernel.org

On Tue, Aug 22, 2017 at 1:08 PM, Anton Blanchard <anton@ozlabs.org> wrote:
> Hi Arnd,
>>
>> Note that while clang won't allow certain kinds of variable-length
>> arrays in structures, this particular instance is fine, as the array
>> is at the end of the structure, and the size is strictly bounded.
>
> Unfortunately it doesn't appear to work, at least with ppc64le clang:
>
> fs/ext4/mballoc.c:2303:17: error: fields must have a constant size: 'variable length array in structure' extension will never be supported
>         ext4_grpblk_t counters[blocksize_bits + 2];

My fix for this is in the ext4/dev branch in linux-next, I hope it still
makes it into v4.13.

       Arnd