video: Replace zero-length array with flexible-array member

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 80c49dd975f4 ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200221160005.GA13552@embeddedor

diff --git a/drivers/video/fbdev/mmp/hw/mmp_ctrl.h b/drivers/video/fbdev/mmp/hw/mmp_ctrl.h
index 335d4983dc524847ad118fb4d1dc5cbe8f62b63c..167585a889d318667ebfdc4e5e77bd55c815589d 100644 (file)
--- 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 1a0bd78f93454765986db5e0d39c6a5331f56ec5..12fa1050f3eb9d54f2673e46425e6e53a0652707 100644 (file)
--- 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 1f9bc133e2309c637cd6a6cec884563b772c23d0..77252cb46361f6526a6516cf1c04527dfa639319 100644 (file)
--- 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);