On Wed, Jun 11, 2025 at 01:52:41PM -0600, 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@xxxxxxxxxx>
> ---
> Changes in v3:
> - Use union instead of DEFINE_RAW_FLEX().
I think your TRAILING_OVERLAP macro[1] is perfect here. I'll try to get that
landed for the next rc. Can you double-check that this works correctly
in these cases?
> @@ -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,
I think it would be a pretty small and direct replacement:
TRAILING_OVERLAP(struct nd_cmd_pkg, pkg, nd_payload,
struct nd_intel_get_security_state cmd;
) nd_cmd = {
...
-Kees
[1] https://web.git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git/commit/?h=for-next/kspp&id=29bb79e9dbf1ba100125e39deb7147acd490903f
--
Kees Cook
