| Message ID | 20200319225002.GA28673@embeddedor.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 98d13639e6950b31e2e2e596a9bb58dada8b9f29 |
| Delegated to: | Kalle Valo |
| Headers | show |
| Series | [next] admtek: adm8211.h: Replace zero-length array with flexible-array member | expand |
"Gustavo A. R. Silva" <gustavo@embeddedor.com> 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] > > 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 <gustavo@embeddedor.com> Patch applied to wireless-drivers-next.git, thanks. 98d13639e695 adm80211: Replace zero-length array with flexible-array member
diff --git a/drivers/net/wireless/admtek/adm8211.h b/drivers/net/wireless/admtek/adm8211.h index 2c55c629de28..095625ecb8ff 100644 --- a/drivers/net/wireless/admtek/adm8211.h +++ b/drivers/net/wireless/admtek/adm8211.h @@ -531,7 +531,7 @@ struct adm8211_eeprom { u8 lpf_cutoff[14]; /* 0x62 */ u8 lnags_threshold[14]; /* 0x70 */ __le16 checksum; /* 0x7E */ - u8 cis_data[0]; /* 0x80, 384 bytes */ + u8 cis_data[]; /* 0x80, 384 bytes */ } __packed; struct adm8211_priv {
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] 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 <gustavo@embeddedor.com> --- drivers/net/wireless/admtek/adm8211.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)