| Message ID | 20200305110011.GA21056@embeddedor (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [next] drm/bridge/mhl.h: Replace zero-length array with flexible-array member | expand |
On Thu, Mar 05, 2020 at 05:00:11AM -0600, 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> Applied to drm-misc-next, thanks for your patch. -Daniel > --- > include/drm/bridge/mhl.h | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/include/drm/bridge/mhl.h b/include/drm/bridge/mhl.h > index 1cc77bf38324..d96626a0e3fa 100644 > --- a/include/drm/bridge/mhl.h > +++ b/include/drm/bridge/mhl.h > @@ -327,13 +327,13 @@ struct mhl_burst_bits_per_pixel_fmt { > struct { > u8 stream_id; > u8 pixel_format; > - } __packed desc[0]; > + } __packed desc[]; > } __packed; > > struct mhl_burst_emsc_support { > struct mhl3_burst_header hdr; > u8 num_entries; > - __be16 burst_id[0]; > + __be16 burst_id[]; > } __packed; > > struct mhl_burst_audio_descr { > -- > 2.25.0 >
diff --git a/include/drm/bridge/mhl.h b/include/drm/bridge/mhl.h index 1cc77bf38324..d96626a0e3fa 100644 --- a/include/drm/bridge/mhl.h +++ b/include/drm/bridge/mhl.h @@ -327,13 +327,13 @@ struct mhl_burst_bits_per_pixel_fmt { struct { u8 stream_id; u8 pixel_format; - } __packed desc[0]; + } __packed desc[]; } __packed; struct mhl_burst_emsc_support { struct mhl3_burst_header hdr; u8 num_entries; - __be16 burst_id[0]; + __be16 burst_id[]; } __packed; struct mhl_burst_audio_descr {
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> --- include/drm/bridge/mhl.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)