RE: [PATCH v2] ACPICA: Replace one-element array with flexible-array

[Kaneda, Erik]

> -----Original Message-----
> From: linux-acpi-owner@xxxxxxxxxxxxxxx <linux-acpi-
> owner@xxxxxxxxxxxxxxx> On Behalf Of Kaneda, Erik
> Sent: Wednesday, June 3, 2020 4:13 PM
> To: Rafael J. Wysocki <rafael@xxxxxxxxxx>; Gustavo A. R. Silva
> <gustavoars@xxxxxxxxxx>
> Cc: Moore, Robert <robert.moore@xxxxxxxxx>; Wysocki, Rafael J
> <rafael.j.wysocki@xxxxxxxxx>; Len Brown <lenb@xxxxxxxxxx>; ACPI Devel
> Maling List <linux-acpi@xxxxxxxxxxxxxxx>; open list:ACPI COMPONENT
> ARCHITECTURE (ACPICA) <devel@xxxxxxxxxx>; Linux Kernel Mailing List
> <linux-kernel@xxxxxxxxxxxxxxx>; Gustavo A. R. Silva
> <gustavo@xxxxxxxxxxxxxx>
> Subject: RE: [PATCH v2] ACPICA: Replace one-element array with flexible-
> array
> 
> 
> 
> > -----Original Message-----
> > From: linux-acpi-owner@xxxxxxxxxxxxxxx <linux-acpi-
> > owner@xxxxxxxxxxxxxxx> On Behalf Of Rafael J. Wysocki
> > Sent: Wednesday, June 3, 2020 6:04 AM
> > To: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>; Kaneda, Erik
> > <erik.kaneda@xxxxxxxxx>
> > Cc: Moore, Robert <robert.moore@xxxxxxxxx>; Wysocki, Rafael J
> > <rafael.j.wysocki@xxxxxxxxx>; Len Brown <lenb@xxxxxxxxxx>; ACPI Devel
> > Maling List <linux-acpi@xxxxxxxxxxxxxxx>; open list:ACPI COMPONENT
> > ARCHITECTURE (ACPICA) <devel@xxxxxxxxxx>; Linux Kernel Mailing List
> > <linux-kernel@xxxxxxxxxxxxxxx>; Gustavo A. R. Silva
> > <gustavo@xxxxxxxxxxxxxx>
> > Subject: Re: [PATCH v2] ACPICA: Replace one-element array with
> > flexible- array
> >
> > On Tue, Jun 2, 2020 at 11:34 PM Gustavo A. R. Silva
> > <gustavoars@xxxxxxxxxx>
> > wrote:
> > >
> > > The current codebase makes use of one-element arrays in the
> > > following
> > > form:
> > >
> > > struct something {
> > >     int length;
> > >     u8 data[1];
> > > };
> > >
> > > struct something *instance;
> > >
> > > instance = kmalloc(sizeof(*instance) + size, GFP_KERNEL);
> > > instance->length = size;
> > > memcpy(instance->data, source, size);
> > >
> > > 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.
> > >
> > > This issue was found with the help of Coccinelle and audited _manually_.
> > >
> > > [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@xxxxxxxxxx>
> >
> > Erik, can you take this to the upstream, please?
> Yes, We'll have to make additional changes to other structures with one-
> element arrays but we'll get this in time for the upcoming ACPICA release.

Pull request available here: https://github.com/acpica/acpica/pull/608

Erik
> 
> Thanks,
> Erik
> >
> > > ---
> > > Changes in v2:
> > >  - Don't use struct_size() for now.
> > >  - Update subject line and changelog text.
> > >
> > >  drivers/acpi/acpica/utids.c | 2 +-
> > >  include/acpi/actypes.h      | 2 +-
> > >  2 files changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/acpi/acpica/utids.c
> > > b/drivers/acpi/acpica/utids.c index 3bb06935a2ad3..225f3c60203c7
> > > 100644
> > > --- a/drivers/acpi/acpica/utids.c
> > > +++ b/drivers/acpi/acpica/utids.c
> > > @@ -263,7 +263,7 @@ acpi_ut_execute_CID(struct
> acpi_namespace_node
> > *device_node,
> > >          * 3) Size of the actual CID strings
> > >          */
> > >         cid_list_size = sizeof(struct acpi_pnp_device_id_list) +
> > > -           ((count - 1) * sizeof(struct acpi_pnp_device_id)) +
> > > +           count * sizeof(struct acpi_pnp_device_id) +
> > >             string_area_size;
> > >
> > >         cid_list = ACPI_ALLOCATE_ZEROED(cid_list_size);
> > > diff --git a/include/acpi/actypes.h b/include/acpi/actypes.h index
> > > 4defed58ea338..c7bcda0ad366a 100644
> > > --- a/include/acpi/actypes.h
> > > +++ b/include/acpi/actypes.h
> > > @@ -1145,7 +1145,7 @@ struct acpi_pnp_device_id {  struct
> > > acpi_pnp_device_id_list {
> > >         u32 count;              /* Number of IDs in Ids array */
> > >         u32 list_size;          /* Size of list, including ID strings */
> > > -       struct acpi_pnp_device_id ids[1];       /* ID array */
> > > +       struct acpi_pnp_device_id ids[];        /* ID array */
> > >  };
> > >
> > >  /*
> > > --
> > > 2.27.0
> > >