of: of_private.h: 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
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>
Signed-off-by: Rob Herring <robh@kernel.org>

diff --git a/drivers/of/of_private.h b/drivers/of/of_private.h
index 207863c151a501ca788e5c4bca79a9e63a8f08ec..edc682249c00156a37b8d30caaaca00e29a1bcc5 100644 (file)
--- a/drivers/of/of_private.h
+++ b/drivers/of/of_private.h
@@ -24,7 +24,7 @@ struct alias_prop {
        const char *alias;
        struct device_node *np;
        int id;
-       char stem[0];
+       char stem[];
 };
 
 #if defined(CONFIG_SPARC)