From: Gustavo A. R. Silva <gustavo@embeddedor.com>
Date: Thu, 19 Mar 2020 23:10:58 +0000 (-0500)
Subject: of: of_private.h: Replace zero-length array with flexible-array member
X-Git-Tag: v5.7-rc1~111^2~17
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f43775625e28703469198657392168c5fe961edc;p=thirdparty%2Fkernel%2Flinux.git

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 207863c151a50..edc682249c001 100644
--- 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)