net: mlxfw: Replace zero-length array with flexible-array member
Subsystems (3)
PATCH 1/1 net: mlxfw: Replace zero-length array with flexible-array member
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")
--- drivers/net/ethernet/mellanox/mlxfw/mlxfw_mfa2.c | 2 +- drivers/net/ethernet/mellanox/mlxfw/mlxfw_mfa2_tlv.h | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-)
drivers/net/ethernet/mellanox/mlxfw/mlxfw_mfa2.c +1 -1
@@ -496,7 +496,7 @@ mlxfw_mfa2_file_component_tlv_get(const struct mlxfw_mfa2_file *mfa2_file,struct mlxfw_mfa2_comp_data {struct mlxfw_mfa2_component comp; -u8 buff[0 ]; +u8 buff[]; }; static const struct mlxfw_mfa2_tlv_component_descriptor *
drivers/net/ethernet/mellanox/mlxfw/mlxfw_mfa2_tlv.h +1 -1
@@ -11,7 +11,7 @@ struct mlxfw_mfa2_tlv {u8 version;u8 type;__be16 len; -u8 data[0 ]; +u8 data[]; } __packed; static inline const struct mlxfw_mfa2_tlv *
Signature · 1 line
2.25.0
Quoted 22 lines · Mon, Mar 02, 2020 at 10:04:37PM CET, [email protected] 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]
Quoted 7 lines
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] commit76497732932f("cxgb3/l2t: Fix undefined behaviour")Signed-off-by Gustavo A. R. Silva <[email protected]>
From: "Gustavo A. R. Silva" <[email protected]>
Date: Mon, 2 Mar 2020 15:04:37 -0600
Quoted 22 lines
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]
Quoted 7 lines
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] commit76497732932f("cxgb3/l2t: Fix undefined behaviour")Signed-off-by Gustavo A. R. Silva <[email protected]>
Applied.