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 <[email protected]>
---
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);
--
2.25.0
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 <[email protected]>
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);
>