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> --- include/linux/mlx4/qp.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/mlx4/qp.h b/include/linux/mlx4/qp.h index 8e2828d48d7f..9db93e487496 100644 --- a/include/linux/mlx4/qp.h +++ b/include/linux/mlx4/qp.h @@ -362,7 +362,7 @@ struct mlx4_wqe_datagram_seg { struct mlx4_wqe_lso_seg { __be32 mss_hdr_size; - __be32 header[0]; + __be32 header[]; }; enum mlx4_wqe_bind_seg_flags2 {
On Thu, 7 May 2020 13:59:21 -0500 Gustavo A. R. Silva 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[];
> };
>
> ...
Applied, thank you!
On Thu, May 07, 2020 at 01:59:21PM -0500, Gustavo A. R. Silva 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>
> ---
> include/linux/mlx4/qp.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
Applied to for-next, thanks
Jason
On Wed, May 13, 2020 at 03:33:35PM -0300, Jason Gunthorpe wrote: > On Thu, May 07, 2020 at 01:59:21PM -0500, Gustavo A. R. Silva 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> > > --- > > include/linux/mlx4/qp.h | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > Applied to for-next, thanks Jason, Please be cautious here, Jakub already applied this patch. https://lore.kernel.org/lkml/20200509205151.209bdc9d@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com/ > > Jason
On Sat, May 09, 2020 at 08:51:50PM -0700, Jakub Kicinski wrote:
> On Thu, 7 May 2020 13:59:21 -0500 Gustavo A. R. Silva 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[];
> > };
> >
> > ...
>
> Applied, thank you!
Jakub,
Please don't take RDMA patches in netdev unless it is a special
case. There is alot of cross posting and they often get into both
patchworks.
Thanks,
Jason
On Wed, 13 May 2020 15:43:16 -0300 Jason Gunthorpe wrote:
> On Sat, May 09, 2020 at 08:51:50PM -0700, Jakub Kicinski wrote:
> > On Thu, 7 May 2020 13:59:21 -0500 Gustavo A. R. Silva 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[];
> > > };
> > >
> > > ...
> >
> > Applied, thank you!
>
> Jakub,
>
> Please don't take RDMA patches in netdev unless it is a special
> case. There is alot of cross posting and they often get into both
> patchworks.
Sorry about that, I only looked at the subject after applying.