* [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 related [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
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