| Message ID | 20200221160005.GA13552@embeddedor (mailing list archive) |
|---|---|
| State | Superseded, archived |
| Headers | show |
| Series | video: Replace zero-length array with flexible-array member | expand |
On 2/21/20 5:00 PM, 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://protect2.fireeye.com/url?k=0e91e8f4-53f6acd2-0e9063bb-0cc47a31384a-8666d8e5380b9caf&u=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 queued for v5.7, thanks. Best regards, -- Bartlomiej Zolnierkiewicz Samsung R&D Institute Poland Samsung Electronics > --- > drivers/video/fbdev/mmp/hw/mmp_ctrl.h | 2 +- > drivers/video/fbdev/ssd1307fb.c | 2 +- > include/video/mmp_disp.h | 2 +- > 3 files changed, 3 insertions(+), 3 deletions(-) > > diff --git a/drivers/video/fbdev/mmp/hw/mmp_ctrl.h b/drivers/video/fbdev/mmp/hw/mmp_ctrl.h > index 335d4983dc52..167585a889d3 100644 > --- a/drivers/video/fbdev/mmp/hw/mmp_ctrl.h > +++ b/drivers/video/fbdev/mmp/hw/mmp_ctrl.h > @@ -1406,7 +1406,7 @@ struct mmphw_ctrl { > > /*pathes*/ > int path_num; > - struct mmphw_path_plat path_plats[0]; > + struct mmphw_path_plat path_plats[]; > }; > > static inline int overlay_is_vid(struct mmp_overlay *overlay) > diff --git a/drivers/video/fbdev/ssd1307fb.c b/drivers/video/fbdev/ssd1307fb.c > index 142535267fec..fb2640fe575a 100644 > --- a/drivers/video/fbdev/ssd1307fb.c > +++ b/drivers/video/fbdev/ssd1307fb.c > @@ -89,7 +89,7 @@ struct ssd1307fb_par { > > struct ssd1307fb_array { > u8 type; > - u8 data[0]; > + u8 data[]; > }; > > static const struct fb_fix_screeninfo ssd1307fb_fix = { > diff --git a/include/video/mmp_disp.h b/include/video/mmp_disp.h > index 1f9bc133e230..77252cb46361 100644 > --- a/include/video/mmp_disp.h > +++ b/include/video/mmp_disp.h > @@ -231,7 +231,7 @@ struct mmp_path { > > /* layers */ > int overlay_num; > - struct mmp_overlay overlays[0]; > + struct mmp_overlay overlays[]; > }; > > extern struct mmp_path *mmp_get_path(const char *name); >
diff --git a/drivers/video/fbdev/mmp/hw/mmp_ctrl.h b/drivers/video/fbdev/mmp/hw/mmp_ctrl.h index 335d4983dc52..167585a889d3 100644 --- a/drivers/video/fbdev/mmp/hw/mmp_ctrl.h +++ b/drivers/video/fbdev/mmp/hw/mmp_ctrl.h @@ -1406,7 +1406,7 @@ struct mmphw_ctrl { /*pathes*/ int path_num; - struct mmphw_path_plat path_plats[0]; + struct mmphw_path_plat path_plats[]; }; static inline int overlay_is_vid(struct mmp_overlay *overlay) diff --git a/drivers/video/fbdev/ssd1307fb.c b/drivers/video/fbdev/ssd1307fb.c index 142535267fec..fb2640fe575a 100644 --- a/drivers/video/fbdev/ssd1307fb.c +++ b/drivers/video/fbdev/ssd1307fb.c @@ -89,7 +89,7 @@ struct ssd1307fb_par { struct ssd1307fb_array { u8 type; - u8 data[0]; + u8 data[]; }; static const struct fb_fix_screeninfo ssd1307fb_fix = { diff --git a/include/video/mmp_disp.h b/include/video/mmp_disp.h index 1f9bc133e230..77252cb46361 100644 --- a/include/video/mmp_disp.h +++ b/include/video/mmp_disp.h @@ -231,7 +231,7 @@ struct mmp_path { /* layers */ int overlay_num; - struct mmp_overlay overlays[0]; + struct mmp_overlay overlays[]; }; extern struct mmp_path *mmp_get_path(const char *name);
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> --- drivers/video/fbdev/mmp/hw/mmp_ctrl.h | 2 +- drivers/video/fbdev/ssd1307fb.c | 2 +- include/video/mmp_disp.h | 2 +- 3 files changed, 3 insertions(+), 3 deletions(-)