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[2001:1c00:c0c:fe00:fc7e:fd47:85c1:1ab3]) by smtp.gmail.com with ESMTPSA id m3sm33958379wrx.9.2020.03.07.04.03.33 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 07 Mar 2020 04:03:34 -0800 (PST) Subject: Re: [PATCH][next] drm/vboxvideo/vboxvideo.h: Replace zero-length array with flexible-array member To: "Gustavo A. R. Silva" , David Airlie , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org References: <20200305105558.GA19124@embeddedor> <8e2ab9a2-fb47-1d61-d09c-0510ad5ee5ff@redhat.com> <20200306104118.GV2363188@phenom.ffwll.local> From: Hans de Goede Message-ID: <2bc072ea-9e18-2d2c-8427-80a721f8750e@redhat.com> Date: Sat, 7 Mar 2020 13:03:33 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200306104118.GV2363188@phenom.ffwll.local> Content-Language: en-US X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" Hi, On 3/6/20 11:41 AM, Daniel Vetter wrote: > On Thu, Mar 05, 2020 at 03:22:38PM +0100, Hans de Goede wrote: >> Hi, >> >> On 3/5/20 11:55 AM, Gustavo A. R. Silva wrote: >>> The current codebase makes use of the zero-length array language >>> extension to the C90 standard, but the preferred mechanism to declare >>> variable-length types such as these ones is a flexible array member[1][2], >>> introduced in C99: >>> >>> struct foo { >>> int stuff; >>> struct boo array[]; >>> }; >>> >>> By making use of the mechanism above, we will get a compiler warning >>> in case the flexible array does not occur last in the structure, which >>> will help us prevent some kind of undefined behavior bugs from being >>> inadvertently introduced[3] to the codebase from now on. >>> >>> Also, notice that, dynamic memory allocations won't be affected by >>> this change: >>> >>> "Flexible array members have incomplete type, and so the sizeof operator >>> may not be applied. As a quirk of the original implementation of >>> zero-length arrays, sizeof evaluates to zero."[1] >>> >>> This issue was found with the help of Coccinelle. >>> >>> [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html >>> [2] https://github.com/KSPP/linux/issues/21 >>> [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") >>> >>> Signed-off-by: Gustavo A. R. Silva >> >> Patch looks good to me: >> >> Reviewed-by: Hans de Goede > > You're also going to push this? r-b by maintainers without any hint to > what's going to happen is always rather confusing. I've pushed this now, sorry for the confusion I will be more clear about my intentions next time. Regards, Hans >>> --- >>> drivers/gpu/drm/vboxvideo/vboxvideo.h | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/drivers/gpu/drm/vboxvideo/vboxvideo.h b/drivers/gpu/drm/vboxvideo/vboxvideo.h >>> index 0592004f71aa..a5de40fe1a76 100644 >>> --- a/drivers/gpu/drm/vboxvideo/vboxvideo.h >>> +++ b/drivers/gpu/drm/vboxvideo/vboxvideo.h >>> @@ -138,7 +138,7 @@ struct vbva_buffer { >>> u32 data_len; >>> /* variable size for the rest of the vbva_buffer area in VRAM. */ >>> - u8 data[0]; >>> + u8 data[]; >>> } __packed; >>> #define VBVA_MAX_RECORD_SIZE (128 * 1024 * 1024) >>> >> > _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel