Messages in this thread Patch in this message | | | Date | Fri, 28 Feb 2020 07:36:41 -0600 | From | "Gustavo A. R. Silva" <> | Subject | [PATCH][next] ipv6: Replace zero-length array with flexible-array member |
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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/ipv6/ah6.c | 2 +- net/ipv6/seg6_iptunnel.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/net/ipv6/ah6.c b/net/ipv6/ah6.c index 95835e8d99aa..871d6e52ec67 100644 --- a/net/ipv6/ah6.c +++ b/net/ipv6/ah6.c @@ -36,7 +36,7 @@ struct tmp_ext { struct in6_addr saddr; #endif struct in6_addr daddr; - char hdrs[0]; + char hdrs[]; }; struct ah_skb_cb { diff --git a/net/ipv6/seg6_iptunnel.c b/net/ipv6/seg6_iptunnel.c index ab7f124ff5d7..d8afe7290de8 100644 --- a/net/ipv6/seg6_iptunnel.c +++ b/net/ipv6/seg6_iptunnel.c @@ -29,7 +29,7 @@ struct seg6_lwt { struct dst_cache cache; - struct seg6_iptunnel_encap tuninfo[0]; + struct seg6_iptunnel_encap tuninfo[]; }; static inline struct seg6_lwt *seg6_lwt_lwtunnel(struct lwtunnel_state *lwt) -- 2.25.0
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