Re: [PATCH] kernel: module: Replace zero-length array with flexible-array member

[Jessica Yu]

+++ Gustavo A. R. Silva [13/02/20 09:14 -0600]:
> 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@xxxxxxxxxxxxxx>

Applied, thanks Gustavo!

Jessica

> ---
> kernel/module.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/module.c b/kernel/module.c
> index 33569a01d6e1..b88ec9cd2a7f 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -1515,7 +1515,7 @@ struct module_sect_attr {
> struct module_sect_attrs {
> 	struct attribute_group grp;
> 	unsigned int nsections;
> -	struct module_sect_attr attrs[0];
> +	struct module_sect_attr attrs[];
> };
>
> static ssize_t module_sect_show(struct module_attribute *mattr,
> @@ -1608,7 +1608,7 @@ static void remove_sect_attrs(struct module *mod)
> struct module_notes_attrs {
> 	struct kobject *dir;
> 	unsigned int notes;
> -	struct bin_attribute attrs[0];
> +	struct bin_attribute attrs[];
> };
>
> static ssize_t module_notes_read(struct file *filp, struct kobject *kobj,
> --
> 2.25.0