Re: [PATCH] platform/x86: i2c-multi-instantiate: Replace zero-length array with flexible-array member

[Hans de Goede]

Hi,


On 2/27/20 8:03 PM, Gustavo A. R. Silva wrote:
> Hi all,
>
> Friendly ping: who can take this?

FWIW, the patch looks good to me:

Reviewed-by: Hans de Goede <hdegoede@xxxxxxxxxx>

Regards,

Hans



> On 2/12/20 18:55, 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]
> >
> > 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>
> > ---
> >   drivers/platform/x86/i2c-multi-instantiate.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/platform/x86/i2c-multi-instantiate.c b/drivers/platform/x86/i2c-multi-instantiate.c
> > index ffb8d5d1eb5f..6acc8457866e 100644
> > --- a/drivers/platform/x86/i2c-multi-instantiate.c
> > +++ b/drivers/platform/x86/i2c-multi-instantiate.c
> > @@ -28,7 +28,7 @@ struct i2c_inst_data {
> >   
> >   struct i2c_multi_inst_data {
> >   	int num_clients;
> > -	struct i2c_client *clients[0];
> > +	struct i2c_client *clients[];
> >   };
> >   
> >   static int i2c_multi_inst_count(struct acpi_resource *ares, void *data)