ALSA: Replace zero-length array with flexible-array

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]

sizeof(flexible-array-member) triggers a warning because flexible array
members have incomplete type[1]. There are some instances of code in
which the sizeof operator is being incorrectly/erroneously applied to
zero-length arrays and the result is zero. Such instances may be hiding
some bugs. So, this work (flexible-array member conversions) will also
help to get completely rid of those sorts of issues.

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 <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/20200507192223.GA16335@embeddedor
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/include/sound/control.h b/include/sound/control.h
index 11feeee31e3598fba220a2f8bba266a240843952..aeaed2a05baeeb3dc28c60c7d67a7238fdf87ad5 100644 (file)
--- a/include/sound/control.h
+++ b/include/sound/control.h
@@ -75,7 +75,7 @@ struct snd_kcontrol {
        unsigned long private_value;
        void *private_data;
        void (*private_free)(struct snd_kcontrol *kcontrol);
-       struct snd_kcontrol_volatile vd[0];     /* volatile data */
+       struct snd_kcontrol_volatile vd[];      /* volatile data */
 };
 
 #define snd_kcontrol(n) list_entry(n, struct snd_kcontrol, list)

diff --git a/include/sound/intel-nhlt.h b/include/sound/intel-nhlt.h
index f657fd8fc0add82ae21056ac37c19365187c8e17..743c2f4422806284bdfef931aad87a4e91c10d6b 100644 (file)
--- a/include/sound/intel-nhlt.h
+++ b/include/sound/intel-nhlt.h
@@ -50,7 +50,7 @@ enum nhlt_device_type {
 
 struct nhlt_specific_cfg {
        u32 size;
-       u8 caps[0];
+       u8 caps[];
 } __packed;
 
 struct nhlt_fmt_cfg {
@@ -60,7 +60,7 @@ struct nhlt_fmt_cfg {
 
 struct nhlt_fmt {
        u8 fmt_count;
-       struct nhlt_fmt_cfg fmt_config[0];
+       struct nhlt_fmt_cfg fmt_config[];
 } __packed;
 
 struct nhlt_endpoint {
@@ -80,7 +80,7 @@ struct nhlt_endpoint {
 struct nhlt_acpi_table {
        struct acpi_table_header header;
        u8 endpoint_count;
-       struct nhlt_endpoint desc[0];
+       struct nhlt_endpoint desc[];
 } __packed;
 
 struct nhlt_resource_desc  {

diff --git a/sound/core/oss/pcm_plugin.h b/sound/core/oss/pcm_plugin.h
index 8d2f7a4e3ab679b509519aa9e90915e5f2cb95f9..46e273bd4a7866b7a4661f679833b4ab205c276d 100644 (file)
--- a/sound/core/oss/pcm_plugin.h
+++ b/sound/core/oss/pcm_plugin.h
@@ -64,7 +64,7 @@ struct snd_pcm_plugin {
        char *buf;
        snd_pcm_uframes_t buf_frames;
        struct snd_pcm_plugin_channel *buf_channels;
-       char extra_data[0];
+       char extra_data[];
 };
 
 int snd_pcm_plugin_build(struct snd_pcm_substream *handle,

diff --git a/sound/usb/usx2y/usbusx2y.h b/sound/usb/usx2y/usbusx2y.h
index e0f77172ce8fcc7b4d9820af7f1fea86c85074a3..144b85f57bd2a6a45753255da5affe6db2c2f6f2 100644 (file)
--- a/sound/usb/usx2y/usbusx2y.h
+++ b/sound/usb/usx2y/usbusx2y.h
@@ -18,7 +18,7 @@ struct snd_usX2Y_AsyncSeq {
 struct snd_usX2Y_urbSeq {
        int     submitted;
        int     len;
-       struct urb      *urb[0];
+       struct urb      *urb[];
 };
 
 #include "usx2yhwdeppcm.h"