lkml.org 
[lkml]   [2020]   [Mar]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[PATCH][next] udf: udf_sb.h: 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 76497732932f ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
---
fs/udf/udf_sb.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/udf/udf_sb.h b/fs/udf/udf_sb.h
index 3d83be54c474..65280ae009e0 100644
--- a/fs/udf/udf_sb.h
+++ b/fs/udf/udf_sb.h
@@ -83,7 +83,7 @@ struct udf_virtual_data {
struct udf_bitmap {
__u32 s_extPosition;
int s_nr_groups;
- struct buffer_head *s_block_bitmap[0];
+ struct buffer_head *s_block_bitmap[];
};

struct udf_part_map {
--
2.25.0
\
 
 \ /
  Last update: 2020-03-09 21:48    [W:0.045 / U:0.040 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site