[PATCH] ALSA: fireworks: 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 --- sound/firewire/fireworks/fireworks.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/sound/firewire/fireworks/fireworks.h b/sound/firewire/fireworks/fireworks.h index dda797209a27..654e28a6669f 100644 --- a/sound/firewire/fireworks/fireworks.h +++ b/sound/firewire/fireworks/fireworks.h @@ -177,7 +177,7 @@ struct snd_efw_phys_meters { u32 in_meters; u32 reserved4; u32 reserved5; - u32 values[0]; + u32 values[]; } __packed; enum snd_efw_clock_source { SND_EFW_CLOCK_SOURCE_INTERNAL = 0,
On Thu, May 07, 2020 at 01:52:45PM -0500, 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 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
sound/firewire/fireworks/fireworks.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
Acked-by: Takashi Sakamoto o-takashi@sakamocchi.jp
diff --git a/sound/firewire/fireworks/fireworks.h b/sound/firewire/fireworks/fireworks.h index dda797209a27..654e28a6669f 100644 --- a/sound/firewire/fireworks/fireworks.h +++ b/sound/firewire/fireworks/fireworks.h @@ -177,7 +177,7 @@ struct snd_efw_phys_meters { u32 in_meters; u32 reserved4; u32 reserved5;
- u32 values[0];
- u32 values[];
} __packed; enum snd_efw_clock_source { SND_EFW_CLOCK_SOURCE_INTERNAL = 0,
Thanks
Takashi Sakamoto
On Thu, 07 May 2020 20:52:45 +0200, 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 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
Applied, thanks.
Takashi
participants (3)
-
Gustavo A. R. Silva -
Takashi Iwai -
Takashi Sakamoto