Linux Input Archive on lore.kernel.org
 help / color / Atom feed
* [PATCH][next] intel-ish-hid: ishtp: ishtp-dev.h: Replace zero-length array with flexible-array member
@ 2020-03-19 21:31 Gustavo A. R. Silva
  2020-03-20 23:08 ` Jiri Kosina
  0 siblings, 1 reply; 2+ messages in thread
From: Gustavo A. R. Silva @ 2020-03-19 21:31 UTC (permalink / raw)
  To: Srinivas Pandruvada, Jiri Kosina, Benjamin Tissoires
  Cc: linux-input, 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/hid/intel-ish-hid/ishtp/ishtp-dev.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/hid/intel-ish-hid/ishtp/ishtp-dev.h b/drivers/hid/intel-ish-hid/ishtp/ishtp-dev.h
index 39e0e6c73adf..1cc6364aa957 100644
--- a/drivers/hid/intel-ish-hid/ishtp/ishtp-dev.h
+++ b/drivers/hid/intel-ish-hid/ishtp/ishtp-dev.h
@@ -214,7 +214,7 @@ struct ishtp_device {
 	const struct ishtp_hw_ops *ops;
 	size_t	mtu;
 	uint32_t	ishtp_msg_hdr;
-	char hw[0] __aligned(sizeof(void *));
+	char hw[] __aligned(sizeof(void *));
 };
 
 static inline unsigned long ishtp_secs_to_jiffies(unsigned long sec)
-- 
2.23.0


^ permalink raw reply	[flat|nested] 2+ messages in thread

* Re: [PATCH][next] intel-ish-hid: ishtp: ishtp-dev.h: Replace zero-length array with flexible-array member
  2020-03-19 21:31 [PATCH][next] intel-ish-hid: ishtp: ishtp-dev.h: Replace zero-length array with flexible-array member Gustavo A. R. Silva
@ 2020-03-20 23:08 ` Jiri Kosina
  0 siblings, 0 replies; 2+ messages in thread
From: Jiri Kosina @ 2020-03-20 23:08 UTC (permalink / raw)
  To: Gustavo A. R. Silva
  Cc: Srinivas Pandruvada, Benjamin Tissoires, linux-input, linux-kernel

On Thu, 19 Mar 2020, 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://github.com/KSPP/linux/issues/21
> [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
> 
> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>

Applied, thanks.

-- 
Jiri Kosina
SUSE Labs


^ permalink raw reply	[flat|nested] 2+ messages in thread

end of thread, back to index

Thread overview: 2+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-03-19 21:31 [PATCH][next] intel-ish-hid: ishtp: ishtp-dev.h: Replace zero-length array with flexible-array member Gustavo A. R. Silva
2020-03-20 23:08 ` Jiri Kosina

Linux Input Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-input/0 linux-input/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-input linux-input/ https://lore.kernel.org/linux-input \
		linux-input@vger.kernel.org
	public-inbox-index linux-input

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-input


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