Messages in this thread | | | Subject | Re: [PATCH][next] drm/vboxvideo/vboxvideo.h: Replace zero-length array with flexible-array member | From | Hans de Goede <> | Date | Sat, 7 Mar 2020 13:03:33 +0100 |
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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 <gustavo@embeddedor.com> >> >> Patch looks good to me: >> >> Reviewed-by: Hans de Goede <hdegoede@redhat.com> > > 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) >>> >> >
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