[PATCH] ALSA: core: Replace zero-length array with flexible-array member

[PATCH] ALSA: core: Replace zero-length array with flexible-array member

[Gustavo A. R. Silva]

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@embeddedor.com>
---
 sound/core/oss/rate.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sound/core/oss/rate.c b/sound/core/oss/rate.c
index 2fa9299a440d..e9f20fefb117 100644
--- a/sound/core/oss/rate.c
+++ b/sound/core/oss/rate.c
@@ -47,7 +47,7 @@ struct rate_priv {
 	unsigned int pos;
 	rate_f func;
 	snd_pcm_sframes_t old_src_frames, old_dst_frames;
-	struct rate_channel channels[0];
+	struct rate_channel channels[];
 };
 
 static void rate_init(struct snd_pcm_plugin *plugin)
-- 
2.25.0

Re: [PATCH] ALSA: core: Replace zero-length array with flexible-array member

[Takashi Iwai]

On Tue, 11 Feb 2020 20:39:10 +0100,
Gustavo A. R. Silva wrote:
> 
> 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@embeddedor.com>

Applied, thanks.


Takashi