* [PATCH] carl9170: Replace zero-length array with flexible-array
@ 2020-05-07 15:19 Gustavo A. R. Silva
2020-05-12 7:32 ` Kalle Valo
0 siblings, 1 reply; 2+ messages in thread
From: Gustavo A. R. Silva @ 2020-05-07 15:19 UTC (permalink / raw)
To: Christian Lamparter, Kalle Valo, David S. Miller
Cc: linux-wireless, netdev, linux-kernel, 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
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>
---
drivers/net/wireless/ath/carl9170/fwcmd.h | 2 +-
drivers/net/wireless/ath/carl9170/hw.h | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/net/wireless/ath/carl9170/fwcmd.h b/drivers/net/wireless/ath/carl9170/fwcmd.h
index ea1d80f9a50e..56999a3b9d3b 100644
--- a/drivers/net/wireless/ath/carl9170/fwcmd.h
+++ b/drivers/net/wireless/ath/carl9170/fwcmd.h
@@ -127,7 +127,7 @@ struct carl9170_write_reg {
struct carl9170_write_reg_byte {
__le32 addr;
__le32 count;
- u8 val[0];
+ u8 val[];
} __packed;
#define CARL9170FW_PHY_HT_ENABLE 0x4
diff --git a/drivers/net/wireless/ath/carl9170/hw.h b/drivers/net/wireless/ath/carl9170/hw.h
index 08e0ae9c5836..555ad4975970 100644
--- a/drivers/net/wireless/ath/carl9170/hw.h
+++ b/drivers/net/wireless/ath/carl9170/hw.h
@@ -851,7 +851,7 @@ struct ar9170_stream {
__le16 length;
__le16 tag;
- u8 payload[0];
+ u8 payload[];
} __packed __aligned(4);
#define AR9170_STREAM_LEN 4
--
2.26.2
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] carl9170: Replace zero-length array with flexible-array
2020-05-07 15:19 [PATCH] carl9170: Replace zero-length array with flexible-array Gustavo A. R. Silva
@ 2020-05-12 7:32 ` Kalle Valo
0 siblings, 0 replies; 2+ messages in thread
From: Kalle Valo @ 2020-05-12 7:32 UTC (permalink / raw)
To: Gustavo A. R. Silva
Cc: Christian Lamparter, David S. Miller, linux-wireless, netdev,
linux-kernel, Gustavo A. R. Silva
"Gustavo A. R. Silva" <gustavoars@kernel.org> 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>
> Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Patch applied to ath-next branch of ath.git, thanks.
103dc3dab295 carl9170: Replace zero-length array with flexible-array
--
https://patchwork.kernel.org/patch/11534317/
https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches
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