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From: Guenter Roeck <linux@roeck-us.net>
To: "David S . Miller" <davem@davemloft.net>
Cc: sparclinux@vger.kernel.org, linux-kernel@vger.kernel.org,
	Guenter Roeck <linux@roeck-us.net>,
	Arnd Bergmann <arnd@kernel.org>,
	David Laight <David.Laight@ACULAB.COM>,
	Anatoly Pugachev <matorola@gmail.com>,
	Sam Ravnborg <sam@ravnborg.org>
Subject: [PATCH v2] sparc: mdesc: Fix compile error seen with gcc 11.x
Date: Tue, 14 Sep 2021 15:47:09 -0700	[thread overview]
Message-ID: <20210914224709.601156-1-linux@roeck-us.net> (raw)

sparc64 images fail to compile with gcc 11.x, reporting the following
errors.

arch/sparc/kernel/mdesc.c:647:22: error:
	'strcmp' reading 1 or more bytes from a region of size 0
arch/sparc/kernel/mdesc.c:692:22: error:
	'strcmp' reading 1 or more bytes from a region of size 0
arch/sparc/kernel/mdesc.c:719:21:
	error: 'strcmp' reading 1 or more bytes from a region of size 0

The underlying problem is that node_block() returns a pointer beyond
the end of struct mdesc_hdr. gcc 11.x detects that and reports the error.
Adding an additional zero-length field to struct mdesc_hdr and pointing
to that field fixes the problem.

Cc: Arnd Bergmann <arnd@kernel.org>
Cc: David Laight <David.Laight@ACULAB.COM>
Cc: Anatoly Pugachev <matorola@gmail.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
v2: data[0] => data[]

I am not sure if there was agreement to accept this patch or not, but
I was asked to resend it with the above change, so here it is. An open
question was if it is acceptable to have a structure named xxx_hdr
include an element pointing to the data following that header.

If this patch is not acceptable, the patch in buildbot may be a possible
alternative to consider.
    https://git.busybox.net/buildroot/commit/?id=6e1106b4a9aee25d1556310d5cd1cb6dde2e6e3f

 arch/sparc/kernel/mdesc.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/sparc/kernel/mdesc.c b/arch/sparc/kernel/mdesc.c
index 8e645ddac58e..83e1f699bc32 100644
--- a/arch/sparc/kernel/mdesc.c
+++ b/arch/sparc/kernel/mdesc.c
@@ -39,6 +39,7 @@ struct mdesc_hdr {
 	u32	node_sz; /* node block size */
 	u32	name_sz; /* name block size */
 	u32	data_sz; /* data block size */
+	char	data[];
 } __attribute__((aligned(16)));
 
 struct mdesc_elem {
@@ -612,7 +613,7 @@ EXPORT_SYMBOL(mdesc_get_node_info);
 
 static struct mdesc_elem *node_block(struct mdesc_hdr *mdesc)
 {
-	return (struct mdesc_elem *) (mdesc + 1);
+	return (struct mdesc_elem *) (mdesc->data);
 }
 
 static void *name_block(struct mdesc_hdr *mdesc)
-- 
2.33.0


             reply	other threads:[~2021-09-14 22:47 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-14 22:47 Guenter Roeck [this message]
2021-09-15  8:38 ` David Laight
2021-09-15 14:04 ` Arnd Bergmann

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