linux-kernel - [PATCH] ALSA: usb-midi: Replace zero-length array with flexible-array member

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Message-ID: <20200211194224.GA9383@embeddedor>
Date:   Tue, 11 Feb 2020 13:42:24 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Clemens Ladisch <clemens@...isch.de>,
        Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>
Cc:     alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Subject: [PATCH] ALSA: usb-midi: 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>
---
 sound/usb/midi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sound/usb/midi.c b/sound/usb/midi.c
index b737f0ec77d0..f15d36731cbe 100644
--- a/sound/usb/midi.c
+++ b/sound/usb/midi.c
@@ -91,7 +91,7 @@ struct usb_ms_endpoint_descriptor {
 	__u8  bDescriptorType;
 	__u8  bDescriptorSubtype;
 	__u8  bNumEmbMIDIJack;
-	__u8  baAssocJackID[0];
+	__u8  baAssocJackID[];
 } __attribute__ ((packed));
 
 struct snd_usb_midi_in_endpoint;
-- 
2.25.0