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

["Gustavo A. R. Silva" <gustavo@embeddedor.com>]

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@kernel.org>
>>> ---
>>> 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