| Message ID | 20200504200838.GA31974@embeddedor (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | ee4dd7061891d7295328302104037520d831ce43 |
| Delegated to: | Kalle Valo |
| Headers | show |
| Series | ath6kl: Replace zero-length array with flexible-array | 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] > > 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 <gustavo@embeddedor.com> > Signed-off-by: Kalle Valo <kvalo@codeaurora.org> Patch applied to ath-next branch of ath.git, thanks. ee4dd7061891 ath6kl: Replace zero-length array with flexible-array
diff --git a/drivers/net/wireless/ath/ath6kl/core.h b/drivers/net/wireless/ath/ath6kl/core.h index 0d30e762c090..77e052336eb5 100644 --- a/drivers/net/wireless/ath/ath6kl/core.h +++ b/drivers/net/wireless/ath/ath6kl/core.h @@ -160,7 +160,7 @@ enum ath6kl_fw_capability { struct ath6kl_fw_ie { __le32 id; __le32 len; - u8 data[0]; + u8 data[]; }; enum ath6kl_hw_flags { @@ -406,7 +406,7 @@ struct ath6kl_mgmt_buff { u32 id; bool no_cck; size_t len; - u8 buf[0]; + u8 buf[]; }; struct ath6kl_sta { diff --git a/drivers/net/wireless/ath/ath6kl/debug.c b/drivers/net/wireless/ath/ath6kl/debug.c index 54337d60f288..7506cea46f58 100644 --- a/drivers/net/wireless/ath/ath6kl/debug.c +++ b/drivers/net/wireless/ath/ath6kl/debug.c @@ -30,7 +30,7 @@ struct ath6kl_fwlog_slot { __le32 length; /* max ATH6KL_FWLOG_PAYLOAD_SIZE bytes */ - u8 payload[0]; + u8 payload[]; }; #define ATH6KL_FWLOG_MAX_ENTRIES 20 diff --git a/drivers/net/wireless/ath/ath6kl/hif.h b/drivers/net/wireless/ath/ath6kl/hif.h index dc6bd8cd9b83..aea7fea2a81e 100644 --- a/drivers/net/wireless/ath/ath6kl/hif.h +++ b/drivers/net/wireless/ath/ath6kl/hif.h @@ -199,7 +199,7 @@ struct hif_scatter_req { u32 scat_q_depth; - struct hif_scatter_item scat_list[0]; + struct hif_scatter_item scat_list[]; }; struct ath6kl_irq_proc_registers {
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 <gustavo@embeddedor.com> --- drivers/net/wireless/ath/ath6kl/core.h | 4 ++-- drivers/net/wireless/ath/ath6kl/debug.c | 2 +- drivers/net/wireless/ath/ath6kl/hif.h | 2 +- 3 files changed, 4 insertions(+), 4 deletions(-)