| Message ID | 20200507185132.GA14046@embeddedor (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | Kalle Valo |
| Headers | show |
| Series | carl9170: Replace zero-length array with flexible-array | expand |
"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> This was sent twice so I'm dropping this version. Patch set to Superseded.
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
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(-)