[kojiws]

Summary

Some compilers, such as Renesas CC-RH, provide no way to specify the
alignment of a type or member. WH_ALIGN8 cannot be implemented for them.
whFlashUnit can then only have the ABI alignment of uint64_t, which can be
less than 8. The 8-byte alignment static_assert in wh_flash_unit.h can never
pass on these compilers, so wolfHSM cannot be built for them.

On many such platforms the flash driver accepts byte buffers with no
alignment requirement. There, the 8-byte alignment of whFlashUnit is not
needed, because NVM reads and writes whFlashUnit contents byte by byte
(nfLoad* / nfStore*). This change lets those platforms build by skipping
the alignment check.

Changes

• Add an opt-in WOLFHSM_CFG_FLASH_UNIT_NO_ALIGN8_CHECK. When it is defined,
  the whFlashUnit 8-byte alignment check (struct whFlashUnitAlignmentCheck
  and its static_assert) is skipped. The size check stays.
• Document the option in wh_settings.h. The documentation states that flash
  callbacks must not assume 8-byte aligned buffers when the option is defined.

Testing

• make and make run in test/ with FLASH_UNIT_SIZE=8 and
  FLASH_UNIT_SIZE=16: built with no warnings and all tests passed.
• Simulated a compiler without an alignment attribute using clang, with an
  empty WH_ALIGN8 and #pragma pack(4) so that uint64_t is 4-byte
  aligned:
  • Without the option, the alignment static_assert fails as before.
  • With the option, the build succeeds for unit sizes 8 and 16.

[Copilot]

🟢 Approval recommended

No active review issues remain for the opt-in flash-unit alignment-check option.

No open issues 🎉

What changed in this PR

Adds an opt-in configuration option to support compilers that cannot enforce 8-byte alignment for whFlashUnit, while preserving the size check and default alignment validation.

Changes:

• Skip the alignment-check structure and assertion when WOLFHSM_CFG_FLASH_UNIT_NO_ALIGN8_CHECK is defined.
• Document the option and the requirement that flash callbacks accept buffers without guaranteed 8-byte alignment.

File	Description
wolfhsm/​wh_settings.h	Documents the option, its default, and callback alignment requirements.
wolfhsm/​wh_flash_unit.h	Guards alignment validation with the new option while retaining size validation.

_{Review effort: Balanced}