From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Gustavo A. R. Silva" Subject: Re: [PATCH][next] drm: Replace zero-length array with flexible-array member Date: Tue, 3 Mar 2020 12:20:16 -0600 Message-ID: <138ff691-94b3-1ce5-e7fa-e6d7c436bf8e@embeddedor.com> References: <20200225140347.GA22864@embeddedor> <87a756sqdc.fsf@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <87a756sqdc.fsf@intel.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Jani Nikula , Lucas Stach , Russell King , Christian Gmeiner , David Airlie , Daniel Vetter , Patrik Jakobsson , Joonas Lahtinen , Rodrigo Vivi , Rob Clark , Sean Paul , Dave Airlie , Gerd Hoffmann , Hans de Goede , Eric Anholt , VMware Graphics , Thomas Hellstrom , Maarten Lankhorst , Maxime Ripard Cc: etnaviv@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, intel-gfx@lists.freedesktop.org, linux-arm-msm@vger.kernel.org, freedreno@lists.freedesktop.org, virtualization@lists.linux-foundation.org, spice-devel@lists.freedesktop.org List-Id: virtualization@lists.linuxfoundation.org On 2/25/20 08:17, Jani Nikula wrote: > On Tue, 25 Feb 2020, "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 >> --- >> drivers/gpu/drm/etnaviv/etnaviv_gem.h | 2 +- >> drivers/gpu/drm/gma500/intel_bios.h | 2 +- >> drivers/gpu/drm/i915/display/intel_vbt_defs.h | 4 ++-- >> drivers/gpu/drm/i915/gt/intel_lrc.c | 2 +- >> drivers/gpu/drm/i915/i915_gpu_error.h | 2 +- > > Please split out the i915 changes to a separate patch. > Sure thing. I can do that. >> drivers/gpu/drm/msm/msm_gem.h | 2 +- >> drivers/gpu/drm/qxl/qxl_cmd.c | 2 +- >> drivers/gpu/drm/vboxvideo/vboxvideo.h | 2 +- >> drivers/gpu/drm/vc4/vc4_drv.h | 2 +- >> drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c | 2 +- >> drivers/gpu/drm/vmwgfx/vmwgfx_surface.c | 2 +- >> include/drm/bridge/mhl.h | 4 ++-- >> include/drm/drm_displayid.h | 2 +- >> include/uapi/drm/i915_drm.h | 4 ++-- > > Not sure it's worth touching uapi headers. They're full of both [0] and > []. Again, please at least split it to a separate patch to be decided > separately. > Yeah, it's worth it; the purpose of these patches is to replace [0] with [] across the whole tree. Thanks -- Gustavo