Linux-mtd Archive on lore.kernel.org
 help / color / Atom feed
* [PATCH][next] mtd: ubi: ubi-media.h: Replace zero-length array with flexible-array member
@ 2020-03-19 22:44 Gustavo A. R. Silva
  0 siblings, 0 replies; only message in thread
From: Gustavo A. R. Silva @ 2020-03-19 22:44 UTC (permalink / raw)
  To: Richard Weinberger, Miquel Raynal, Vignesh Raghavendra
  Cc: linux-mtd, linux-kernel, Gustavo A. R. Silva

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/mtd/ubi/ubi-media.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/mtd/ubi/ubi-media.h b/drivers/mtd/ubi/ubi-media.h
index b5fe8f82281b..386db0598e95 100644
--- a/drivers/mtd/ubi/ubi-media.h
+++ b/drivers/mtd/ubi/ubi-media.h
@@ -498,6 +498,6 @@ struct ubi_fm_volhdr {
 struct ubi_fm_eba {
 	__be32 magic;
 	__be32 reserved_pebs;
-	__be32 pnum[0];
+	__be32 pnum[];
 } __packed;
 #endif /* !__UBI_MEDIA_H__ */
-- 
2.23.0


______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/

^ permalink raw reply	[flat|nested] only message in thread

only message in thread, back to index

Thread overview: (only message) (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-03-19 22:44 [PATCH][next] mtd: ubi: ubi-media.h: Replace zero-length array with flexible-array member Gustavo A. R. Silva

Linux-mtd Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-mtd/0 linux-mtd/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-mtd linux-mtd/ https://lore.kernel.org/linux-mtd \
		linux-mtd@lists.infradead.org
	public-inbox-index linux-mtd

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.infradead.lists.linux-mtd


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git