Re: [PATCH v3][next] acpi: nfit: intel: avoid multiple -Wflex-array-member-not-at-end warnings

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

Hi all,

Friendly ping: who can review or take this, please? :)

Thanks!
-Gustavo

On 11/06/25 13:52, 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.
> 
> Refactor multiple structs that contain flexible-array members in the
> middle by replacing them with unions.
> 
> These changes preserve the memory layout while effectively adjusting
> it so that the flexible-array member is always treated as the last
> member.
> 
> With these changes, fix a dozen instances of the following type of
> warning:
> 
> 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 v3:
>   - Use union instead of DEFINE_RAW_FLEX().
> 
> Changes in v2:
>   - Use DEFINE_RAW_FLEX() instead of __struct_group().
>   - Link: https://lore.kernel.org/linux-hardening/Z-QpUcxFCRByYcTA@kspp/
> 
> v1:
>   - Link: https://lore.kernel.org/linux-hardening/Z618ILbAR8YAvTkd@kspp/
> 
>   drivers/acpi/nfit/intel.c | 132 +++++++++++++++++++++++++++++++-------
>   1 file changed, 108 insertions(+), 24 deletions(-)
> 
> diff --git a/drivers/acpi/nfit/intel.c b/drivers/acpi/nfit/intel.c
> index 3902759abcba..987d427ec2b6 100644
> --- a/drivers/acpi/nfit/intel.c
> +++ b/drivers/acpi/nfit/intel.c
> @@ -55,9 +55,16 @@ static unsigned long intel_security_flags(struct nvdimm *nvdimm,
>   {
>   	struct nfit_mem *nfit_mem = nvdimm_provider_data(nvdimm);
>   	unsigned long security_flags = 0;
> -	struct {
> +	/*
> +	 * This effectively creates a union between the flexible-array member
> +	 * and any members after _offset_to_fam.
> +	 */
> +	union {
>   		struct nd_cmd_pkg pkg;
> -		struct nd_intel_get_security_state cmd;
> +		struct {
> +			u8 _offset_to_fam[offsetof(struct nd_cmd_pkg, nd_payload)];
> +			struct nd_intel_get_security_state cmd;
> +		};
>   	} nd_cmd = {
>   		.pkg = {
>   			.nd_command = NVDIMM_INTEL_GET_SECURITY_STATE,
> @@ -120,9 +127,16 @@ static unsigned long intel_security_flags(struct nvdimm *nvdimm,
>   static int intel_security_freeze(struct nvdimm *nvdimm)
>   {
>   	struct nfit_mem *nfit_mem = nvdimm_provider_data(nvdimm);
> -	struct {
> +	/*
> +	 * This effectively creates a union between the flexible-array member
> +	 * and any members after _offset_to_fam.
> +	 */
> +	union {
>   		struct nd_cmd_pkg pkg;
> -		struct nd_intel_freeze_lock cmd;
> +		struct {
> +			u8 _offset_to_fam[offsetof(struct nd_cmd_pkg, nd_payload)];
> +			struct nd_intel_freeze_lock cmd;
> +		};
>   	} nd_cmd = {
>   		.pkg = {
>   			.nd_command = NVDIMM_INTEL_FREEZE_LOCK,
> @@ -153,9 +167,16 @@ static int intel_security_change_key(struct nvdimm *nvdimm,
>   	unsigned int cmd = ptype == NVDIMM_MASTER ?
>   		NVDIMM_INTEL_SET_MASTER_PASSPHRASE :
>   		NVDIMM_INTEL_SET_PASSPHRASE;
> -	struct {
> +	/*
> +	 * This effectively creates a union between the flexible-array member
> +	 * and any members after _offset_to_fam.
> +	 */
> +	union {
>   		struct nd_cmd_pkg pkg;
> -		struct nd_intel_set_passphrase cmd;
> +		struct {
> +			u8 _offset_to_fam[offsetof(struct nd_cmd_pkg, nd_payload)];
> +			struct nd_intel_set_passphrase cmd;
> +		};
>   	} nd_cmd = {
>   		.pkg = {
>   			.nd_family = NVDIMM_FAMILY_INTEL,
> @@ -195,9 +216,16 @@ static int __maybe_unused intel_security_unlock(struct nvdimm *nvdimm,
>   		const struct nvdimm_key_data *key_data)
>   {
>   	struct nfit_mem *nfit_mem = nvdimm_provider_data(nvdimm);
> -	struct {
> +	/*
> +	 * This effectively creates a union between the flexible-array member
> +	 * and any members after _offset_to_fam.
> +	 */
> +	union {
>   		struct nd_cmd_pkg pkg;
> -		struct nd_intel_unlock_unit cmd;
> +		struct {
> +			u8 _offset_to_fam[offsetof(struct nd_cmd_pkg, nd_payload)];
> +			struct nd_intel_unlock_unit cmd;
> +		};
>   	} nd_cmd = {
>   		.pkg = {
>   			.nd_command = NVDIMM_INTEL_UNLOCK_UNIT,
> @@ -234,9 +262,16 @@ static int intel_security_disable(struct nvdimm *nvdimm,
>   {
>   	int rc;
>   	struct nfit_mem *nfit_mem = nvdimm_provider_data(nvdimm);
> -	struct {
> +	/*
> +	 * This effectively creates a union between the flexible-array member
> +	 * and any members after _offset_to_fam.
> +	 */
> +	union {
>   		struct nd_cmd_pkg pkg;
> -		struct nd_intel_disable_passphrase cmd;
> +		struct {
> +			u8 _offset_to_fam[offsetof(struct nd_cmd_pkg, nd_payload)];
> +			struct nd_intel_disable_passphrase cmd;
> +		};
>   	} nd_cmd = {
>   		.pkg = {
>   			.nd_command = NVDIMM_INTEL_DISABLE_PASSPHRASE,
> @@ -277,9 +312,16 @@ static int __maybe_unused intel_security_erase(struct nvdimm *nvdimm,
>   	struct nfit_mem *nfit_mem = nvdimm_provider_data(nvdimm);
>   	unsigned int cmd = ptype == NVDIMM_MASTER ?
>   		NVDIMM_INTEL_MASTER_SECURE_ERASE : NVDIMM_INTEL_SECURE_ERASE;
> -	struct {
> +	/*
> +	 * This effectively creates a union between the flexible-array member
> +	 * and any members after _offset_to_fam.
> +	 */
> +	union {
>   		struct nd_cmd_pkg pkg;
> -		struct nd_intel_secure_erase cmd;
> +		struct {
> +			u8 _offset_to_fam[offsetof(struct nd_cmd_pkg, nd_payload)];
> +			struct nd_intel_secure_erase cmd;
> +		};
>   	} nd_cmd = {
>   		.pkg = {
>   			.nd_family = NVDIMM_FAMILY_INTEL,
> @@ -318,9 +360,16 @@ static int __maybe_unused intel_security_query_overwrite(struct nvdimm *nvdimm)
>   {
>   	int rc;
>   	struct nfit_mem *nfit_mem = nvdimm_provider_data(nvdimm);
> -	struct {
> +	/*
> +	 * This effectively creates a union between the flexible-array member
> +	 * and any members after _offset_to_fam.
> +	 */
> +	union {
>   		struct nd_cmd_pkg pkg;
> -		struct nd_intel_query_overwrite cmd;
> +		struct {
> +			u8 _offset_to_fam[offsetof(struct nd_cmd_pkg, nd_payload)];
> +			struct nd_intel_query_overwrite cmd;
> +		};
>   	} nd_cmd = {
>   		.pkg = {
>   			.nd_command = NVDIMM_INTEL_QUERY_OVERWRITE,
> @@ -354,9 +403,16 @@ static int __maybe_unused intel_security_overwrite(struct nvdimm *nvdimm,
>   {
>   	int rc;
>   	struct nfit_mem *nfit_mem = nvdimm_provider_data(nvdimm);
> -	struct {
> +	/*
> +	 * This effectively creates a union between the flexible-array member
> +	 * and any members after _offset_to_fam.
> +	 */
> +	union {
>   		struct nd_cmd_pkg pkg;
> -		struct nd_intel_overwrite cmd;
> +		struct {
> +			u8 _offset_to_fam[offsetof(struct nd_cmd_pkg, nd_payload)];
> +			struct nd_intel_overwrite cmd;
> +		};
>   	} nd_cmd = {
>   		.pkg = {
>   			.nd_command = NVDIMM_INTEL_OVERWRITE,
> @@ -407,9 +463,16 @@ const struct nvdimm_security_ops *intel_security_ops = &__intel_security_ops;
>   static int intel_bus_fwa_businfo(struct nvdimm_bus_descriptor *nd_desc,
>   		struct nd_intel_bus_fw_activate_businfo *info)
>   {
> -	struct {
> +	/*
> +	 * This effectively creates a union between the flexible-array member
> +	 * and any members after _offset_to_fam.
> +	 */
> +	union {
>   		struct nd_cmd_pkg pkg;
> -		struct nd_intel_bus_fw_activate_businfo cmd;
> +		struct {
> +			u8 _offset_to_fam[offsetof(struct nd_cmd_pkg, nd_payload)];
> +			struct nd_intel_bus_fw_activate_businfo cmd;
> +		};
>   	} nd_cmd = {
>   		.pkg = {
>   			.nd_command = NVDIMM_BUS_INTEL_FW_ACTIVATE_BUSINFO,
> @@ -518,9 +581,16 @@ static enum nvdimm_fwa_capability intel_bus_fwa_capability(
>   static int intel_bus_fwa_activate(struct nvdimm_bus_descriptor *nd_desc)
>   {
>   	struct acpi_nfit_desc *acpi_desc = to_acpi_desc(nd_desc);
> -	struct {
> +	/*
> +	 * This effectively creates a union between the flexible-array member
> +	 * and any members after _offset_to_fam.
> +	 */
> +	union {
>   		struct nd_cmd_pkg pkg;
> -		struct nd_intel_bus_fw_activate cmd;
> +		struct {
> +			u8 _offset_to_fam[offsetof(struct nd_cmd_pkg, nd_payload)];
> +			struct nd_intel_bus_fw_activate cmd;
> +		};
>   	} nd_cmd = {
>   		.pkg = {
>   			.nd_command = NVDIMM_BUS_INTEL_FW_ACTIVATE,
> @@ -582,9 +652,16 @@ const struct nvdimm_bus_fw_ops *intel_bus_fw_ops = &__intel_bus_fw_ops;
>   static int intel_fwa_dimminfo(struct nvdimm *nvdimm,
>   		struct nd_intel_fw_activate_dimminfo *info)
>   {
> -	struct {
> +	/*
> +	 * This effectively creates a union between the flexible-array member
> +	 * and any members after _offset_to_fam.
> +	 */
> +	union {
>   		struct nd_cmd_pkg pkg;
> -		struct nd_intel_fw_activate_dimminfo cmd;
> +		struct {
> +			u8 _offset_to_fam[offsetof(struct nd_cmd_pkg, nd_payload)];
> +			struct nd_intel_fw_activate_dimminfo cmd;
> +		};
>   	} nd_cmd = {
>   		.pkg = {
>   			.nd_command = NVDIMM_INTEL_FW_ACTIVATE_DIMMINFO,
> @@ -688,9 +765,16 @@ static int intel_fwa_arm(struct nvdimm *nvdimm, enum nvdimm_fwa_trigger arm)
>   {
>   	struct nfit_mem *nfit_mem = nvdimm_provider_data(nvdimm);
>   	struct acpi_nfit_desc *acpi_desc = nfit_mem->acpi_desc;
> -	struct {
> +	/*
> +	 * This effectively creates a union between the flexible-array member
> +	 * and any members after _offset_to_fam.
> +	 */
> +	union {
>   		struct nd_cmd_pkg pkg;
> -		struct nd_intel_fw_activate_arm cmd;
> +		struct {
> +			u8 _offset_to_fam[offsetof(struct nd_cmd_pkg, nd_payload)];
> +			struct nd_intel_fw_activate_arm cmd;
> +		};
>   	} nd_cmd = {
>   		.pkg = {
>   			.nd_command = NVDIMM_INTEL_FW_ACTIVATE_ARM,