Re: [PATCH v2][next] acpi: nfit: intel: Avoid multiple -Wflex-array-member-not-at-end warnings

[Gustavo A. R. Silva]

On 30/04/25 13:41, Gustavo A. R. Silva wrote:
> On 27/03/25 08:03, Dan Williams wrote:
> > Gustavo A. R. Silva wrote:
> > > -Wflex-array-member-not-at-end was introduced in GCC-14, and we are
> > > getting ready to enable it, globally.
> > >
> > > Use the `DEFINE_RAW_FLEX()` helper for on-stack definitions of
> > > a flexible structure where the size of the flexible-array member
> > > is known at compile-time, and refactor the rest of the code,
> > > accordingly.
> > >
> > > So, with these changes, fix a dozen of the following warnings:
> > >
> > > drivers/acpi/nfit/intel.c:692:35: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> > >
> > > Signed-off-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
> > > ---
> > > Changes in v2:
> > >   - Use DEFINE_RAW_FLEX() instead of __struct_group().
> > >
> > > v1:
> > >   - Link: https://lore.kernel.org/linux-hardening/Z618ILbAR8YAvTkd@kspp/
> > >
> > >   drivers/acpi/nfit/intel.c | 388 ++++++++++++++++++--------------------
> > >   1 file changed, 179 insertions(+), 209 deletions(-)
> > >
> > > diff --git a/drivers/acpi/nfit/intel.c b/drivers/acpi/nfit/intel.c
> > > index 3902759abcba..114d5b3bb39b 100644
> > > --- a/drivers/acpi/nfit/intel.c
> > > +++ b/drivers/acpi/nfit/intel.c
> > > @@ -55,21 +55,17 @@ static unsigned long intel_security_flags(struct nvdimm *nvdimm,
> > >   {
> > >       struct nfit_mem *nfit_mem = nvdimm_provider_data(nvdimm);
> > >       unsigned long security_flags = 0;
> > > -    struct {
> > > -        struct nd_cmd_pkg pkg;
> > > -        struct nd_intel_get_security_state cmd;
> > > -    } nd_cmd = {
> > > -        .pkg = {
> > > -            .nd_command = NVDIMM_INTEL_GET_SECURITY_STATE,
> > > -            .nd_family = NVDIMM_FAMILY_INTEL,
> > > -            .nd_size_out =
> > > -                sizeof(struct nd_intel_get_security_state),
> > > -            .nd_fw_size =
> > > -                sizeof(struct nd_intel_get_security_state),
> > > -        },
> > > -    };
> > > +    DEFINE_RAW_FLEX(struct nd_cmd_pkg, nd_cmd, nd_payload,
> > > +            sizeof(struct nd_intel_get_security_state));
> > > +    struct nd_intel_get_security_state *cmd =
> > > +            (struct nd_intel_get_security_state *)nd_cmd->nd_payload;
> > >       int rc;
> > > +    nd_cmd->nd_command = NVDIMM_INTEL_GET_SECURITY_STATE;
> > > +    nd_cmd->nd_family = NVDIMM_FAMILY_INTEL;
> > > +    nd_cmd->nd_size_out = sizeof(struct nd_intel_get_security_state);
> > > +    nd_cmd->nd_fw_size = sizeof(struct nd_intel_get_security_state);
> >
> > Can this keep the C99 init-style with something like (untested):
> >
> > _DEFINE_FLEX(struct nd_cmd_pkg, nd_cmd, nd_payload,
> >               sizeof(struct nd_intel_get_security_state), {
> >         .pkg = {
> >                 .nd_command = NVDIMM_INTEL_GET_SECURITY_STATE,
> >                 .nd_family = NVDIMM_FAMILY_INTEL,
> >                 .nd_size_out =
> >                         sizeof(struct nd_intel_get_security_state),
> >                 .nd_fw_size =
> >                         sizeof(struct nd_intel_get_security_state),
> >         },
> >     });
> >
> >
> > ?
>
> The code below works - however, notice that in this case we should
> go through 'obj', which is an object defined in _DEFINE_FLEX().
>
>          _DEFINE_FLEX(struct nd_cmd_pkg, nd_cmd, nd_payload,
>                          sizeof(struct nd_intel_get_security_state), = {
>                  .obj = {
>                          .nd_command = NVDIMM_INTEL_GET_SECURITY_STATE,
>                          .nd_family = NVDIMM_FAMILY_INTEL,
>                          .nd_size_out =
>                                  sizeof(struct nd_intel_get_security_state),
>                          .nd_fw_size =
>                                  sizeof(struct nd_intel_get_security_state),
>                  },
>          });

Now, I can modify the helper like this:

diff --git a/include/linux/overflow.h b/include/linux/overflow.h
index 69533e703be5..170d3cfe7ecc 100644
--- a/include/linux/overflow.h
+++ b/include/linux/overflow.h
@@ -404,7 +404,7 @@ static inline size_t __must_check size_sub(size_t minuend, size_t subtrahend)
        union {                                                                 \
                u8 bytes[struct_size_t(type, member, count)];                   \
                type obj;                                                       \
-       } name##_u initializer;                                                 \
+       } name##_u = { .obj initializer };                                      \
        type *name = (type *)&name##_u

 /**

and then we can use the helper as follows:

        _DEFINE_FLEX(struct nd_cmd_pkg, nd_cmd, nd_payload,
                        sizeof(struct nd_intel_get_security_state), = {
                        .nd_command = NVDIMM_INTEL_GET_SECURITY_STATE,
                        .nd_family = NVDIMM_FAMILY_INTEL,
                        .nd_size_out =
                                sizeof(struct nd_intel_get_security_state),
                        .nd_fw_size =
                                sizeof(struct nd_intel_get_security_state),
        });

OK, I'll go and update the helper.

-Gustavo