linux-kernel - [PATCH] lib/ts_bm: Replace zero-length array with flexible-array member

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Message-ID: <20200211205620.GA24694@embeddedor>
Date:   Tue, 11 Feb 2020 14:56:20 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Subject: [PATCH] lib/ts_bm: Replace zero-length array with flexible-array
 member

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
inadvertenly introduced[3] to the codebase from now on.

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@...eddedor.com>
---
 lib/ts_bm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/ts_bm.c b/lib/ts_bm.c
index 9e66ee4020e9..9d64629fa8b8 100644
--- a/lib/ts_bm.c
+++ b/lib/ts_bm.c
@@ -56,7 +56,7 @@ struct ts_bm
 	u8 *		pattern;
 	unsigned int	patlen;
 	unsigned int 	bad_shift[ASIZE];
-	unsigned int	good_shift[0];
+	unsigned int	good_shift[];
 };
 
 static unsigned int bm_find(struct ts_config *conf, struct ts_state *state)
-- 
2.25.0