From: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
To: Geert Uytterhoeven <geert@linux-m68k.org>,
"Gustavo A. R. Silva" <gustavo@embeddedor.com>
Cc: linux-m68k@lists.linux-m68k.org, linux-kernel@vger.kernel.org
Subject: [PATCH RESEND 1/2][next] m68k: amiga: config: Replace zero-length array with flexible-array member
Date: Mon, 20 Apr 2020 13:14:01 -0500 [thread overview]
Message-ID: <20200420181401.GA32172@embeddedor> (raw)
In-Reply-To: <cover.1585264062.git.gustavo@embeddedor.com>
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>
---
arch/m68k/amiga/config.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/m68k/amiga/config.c b/arch/m68k/amiga/config.c
index c32ab8041cf6..06c15374200e 100644
--- a/arch/m68k/amiga/config.c
+++ b/arch/m68k/amiga/config.c
@@ -628,7 +628,7 @@ struct savekmsg {
unsigned long magic2; /* SAVEKMSG_MAGIC2 */
unsigned long magicptr; /* address of magic1 */
unsigned long size;
- char data[0];
+ char data[];
};
static struct savekmsg *savekmsg;
--
2.26.0
next prev parent reply other threads:[~2020-04-20 18:09 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-26 23:23 [PATCH 0/2][next] m68k: amiga: config: Use flexible-array member and mark expected switch fall-through Gustavo A. R. Silva
2020-03-26 23:29 ` [PATCH 2/2][next] m68k: amiga: config: Mark " Gustavo A. R. Silva
2020-04-20 7:17 ` Geert Uytterhoeven
2020-04-20 16:07 ` Gustavo A. R. Silva
2020-04-20 17:48 ` Geert Uytterhoeven
2020-04-20 18:15 ` Gustavo A. R. Silva
2020-04-20 18:14 ` Gustavo A. R. Silva [this message]
2020-04-21 7:06 ` [PATCH RESEND 1/2][next] m68k: amiga: config: Replace zero-length array with flexible-array member Geert Uytterhoeven
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