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 <[email protected]>
---
drivers/firmware/iscsi_ibft.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/firmware/iscsi_ibft.c b/drivers/firmware/iscsi_ibft.c
index 96758b71a8db..7127a04bca19 100644
--- a/drivers/firmware/iscsi_ibft.c
+++ b/drivers/firmware/iscsi_ibft.c
@@ -104,7 +104,7 @@ struct ibft_control {
u16 tgt0_off;
u16 nic1_off;
u16 tgt1_off;
- u16 expansion[0];
+ u16 expansion[];
} __attribute__((__packed__));
struct ibft_initiator {
Hi all,
Friendly ping: who can take this?
Thanks
--
Gustavo
On Thu, May 07, 2020 at 01:55:44PM -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 <[email protected]>
> ---
> drivers/firmware/iscsi_ibft.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/firmware/iscsi_ibft.c b/drivers/firmware/iscsi_ibft.c
> index 96758b71a8db..7127a04bca19 100644
> --- a/drivers/firmware/iscsi_ibft.c
> +++ b/drivers/firmware/iscsi_ibft.c
> @@ -104,7 +104,7 @@ struct ibft_control {
> u16 tgt0_off;
> u16 nic1_off;
> u16 tgt1_off;
> - u16 expansion[0];
> + u16 expansion[];
> } __attribute__((__packed__));
>
> struct ibft_initiator {
>
On Thu, May 21, 2020 at 01:32:35PM -0500, Gustavo A. R. Silva wrote:
> Hi all,
>
> Friendly ping: who can take this?
It is in the tree. Let me send out a git pull to Linus in a week or two.
Thanks!
>
> Thanks
> --
> Gustavo
>
> On Thu, May 07, 2020 at 01:55:44PM -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 <[email protected]>
> > ---
> > drivers/firmware/iscsi_ibft.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/firmware/iscsi_ibft.c b/drivers/firmware/iscsi_ibft.c
> > index 96758b71a8db..7127a04bca19 100644
> > --- a/drivers/firmware/iscsi_ibft.c
> > +++ b/drivers/firmware/iscsi_ibft.c
> > @@ -104,7 +104,7 @@ struct ibft_control {
> > u16 tgt0_off;
> > u16 nic1_off;
> > u16 tgt1_off;
> > - u16 expansion[0];
> > + u16 expansion[];
> > } __attribute__((__packed__));
> >
> > struct ibft_initiator {
> >