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-8... [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);