* [PATCH][next] batman-adv: Replace zero-length array with flexible-array member
@ 2020-02-17 21:43 Gustavo A. R. Silva
2020-02-17 21:49 ` Sven Eckelmann
0 siblings, 1 reply; 3+ messages in thread
From: Gustavo A. R. Silva @ 2020-02-17 21:43 UTC (permalink / raw)
To: Marek Lindner, Simon Wunderlich, Antonio Quartulli,
Sven Eckelmann, David S. Miller, Jakub Kicinski
Cc: b.a.t.m.a.n, netdev, 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>
---
net/batman-adv/distributed-arp-table.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/batman-adv/distributed-arp-table.c b/net/batman-adv/distributed-arp-table.c
index 3d21dd83f8cc..b85da4b7a77b 100644
--- a/net/batman-adv/distributed-arp-table.c
+++ b/net/batman-adv/distributed-arp-table.c
@@ -88,7 +88,7 @@ struct batadv_dhcp_packet {
__u8 sname[64];
__u8 file[128];
__be32 magic;
- __u8 options[0];
+ __u8 options[];
};
#define BATADV_DHCP_YIADDR_LEN sizeof(((struct batadv_dhcp_packet *)0)->yiaddr)
--
2.25.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH][next] batman-adv: Replace zero-length array with flexible-array member
2020-02-17 21:43 [PATCH][next] batman-adv: Replace zero-length array with flexible-array member Gustavo A. R. Silva
@ 2020-02-17 21:49 ` Sven Eckelmann
2020-02-27 20:06 ` Gustavo A. R. Silva
0 siblings, 1 reply; 3+ messages in thread
From: Sven Eckelmann @ 2020-02-17 21:49 UTC (permalink / raw)
To: Gustavo A. R. Silva
Cc: Marek Lindner, Simon Wunderlich, Antonio Quartulli,
David S. Miller, Jakub Kicinski, b.a.t.m.a.n, netdev,
linux-kernel
[-- Attachment #1: Type: text/plain, Size: 1360 bytes --]
On Monday, 17 February 2020 22:43:00 CET 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>
> ---
> net/batman-adv/distributed-arp-table.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
Applied
Thanks,
Sven
[-- Attachment #2: This is a digitally signed message part. --]
[-- Type: application/pgp-signature, Size: 833 bytes --]
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH][next] batman-adv: Replace zero-length array with flexible-array member
2020-02-17 21:49 ` Sven Eckelmann
@ 2020-02-27 20:06 ` Gustavo A. R. Silva
0 siblings, 0 replies; 3+ messages in thread
From: Gustavo A. R. Silva @ 2020-02-27 20:06 UTC (permalink / raw)
To: Sven Eckelmann
Cc: Marek Lindner, Simon Wunderlich, Antonio Quartulli,
David S. Miller, Jakub Kicinski, b.a.t.m.a.n, netdev,
linux-kernel
On 2/17/20 15:49, Sven Eckelmann wrote:
>>
>> [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>
>> ---
>> net/batman-adv/distributed-arp-table.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> Applied
>
Thanks, Sven.
--
Gustavo
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2020-02-27 20:04 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-02-17 21:43 [PATCH][next] batman-adv: Replace zero-length array with flexible-array member Gustavo A. R. Silva
2020-02-17 21:49 ` Sven Eckelmann
2020-02-27 20:06 ` Gustavo A. R. Silva
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).