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ALSA: Replace zero-length array with flexible-array

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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 7649773293 ("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>
This commit is contained in:
Gustavo A. R. Silva 2020-05-07 14:22:23 -05:00 committed by Takashi Iwai
parent df1fceacb2
commit 9ad06ebb9a
4 changed files with 6 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/sound/control.h
View File

@ -75,7 +75,7 @@ struct snd_kcontrol {
unsigned long private_value; unsigned long private_value;
void *private_data; void *private_data;
void (*private_free)(struct snd_kcontrol *kcontrol); 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) #define snd_kcontrol(n) list_entry(n, struct snd_kcontrol, list)

6
include/sound/intel-nhlt.h
View File

@ -50,7 +50,7 @@ enum nhlt_device_type {
struct nhlt_specific_cfg { struct nhlt_specific_cfg {
u32 size; u32 size;
u8 caps[0]; u8 caps[];
} __packed; } __packed;
struct nhlt_fmt_cfg { struct nhlt_fmt_cfg {
@ -60,7 +60,7 @@ struct nhlt_fmt_cfg {
struct nhlt_fmt { struct nhlt_fmt {
u8 fmt_count; u8 fmt_count;
struct nhlt_fmt_cfg fmt_config[0]; struct nhlt_fmt_cfg fmt_config[];
} __packed; } __packed;
struct nhlt_endpoint { struct nhlt_endpoint {
@ -80,7 +80,7 @@ struct nhlt_endpoint {
struct nhlt_acpi_table { struct nhlt_acpi_table {
struct acpi_table_header header; struct acpi_table_header header;
u8 endpoint_count; u8 endpoint_count;
struct nhlt_endpoint desc[0]; struct nhlt_endpoint desc[];
} __packed; } __packed;
struct nhlt_resource_desc { struct nhlt_resource_desc {

2
sound/core/oss/pcm_plugin.h
View File

@ -64,7 +64,7 @@ struct snd_pcm_plugin {
char *buf; char *buf;
snd_pcm_uframes_t buf_frames; snd_pcm_uframes_t buf_frames;
struct snd_pcm_plugin_channel *buf_channels; struct snd_pcm_plugin_channel *buf_channels;
char extra_data[0]; char extra_data[];
}; };
int snd_pcm_plugin_build(struct snd_pcm_substream *handle, int snd_pcm_plugin_build(struct snd_pcm_substream *handle,

2
sound/usb/usx2y/usbusx2y.h
View File

@ -18,7 +18,7 @@ struct snd_usX2Y_AsyncSeq {
struct snd_usX2Y_urbSeq { struct snd_usX2Y_urbSeq {
int submitted; int submitted;
int len; int len;
struct urb *urb[0]; struct urb *urb[];
}; };
#include "usx2yhwdeppcm.h" #include "usx2yhwdeppcm.h"