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armv9: document Armv9 port MISRA deviations in MISRA.md

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Add three new deviation entries for the ARM_AARCH64_ARMV9 port:

- Directive 4.3 (inline assembly): required to access AArch64 system
  registers with no C equivalent; confined to the port layer
- Rule 5.8 (identifier reuse): pvPortMalloc/vPortFree macro redirect
  to MTE-tagged wrappers, isolating tagging logic in the port
- Rule 11.6 (pointer-to-integer cast): MTE tag stripping requires
  masking pointer bits 56-59 via uintptr_t to recover canonical address
This commit is contained in:
Richard Elberger 2026-06-24 09:12:22 -04:00
parent d18a43e0f0
commit 294945fc99
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MISRA.md
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@ -18,6 +18,16 @@ with ( Assuming rule 8.4 violation; with justification in point 1 ):
grep 'MISRA Ref 8.4.1' . -rI
```
#### Dir 4.3
MISRA C:2012 Dir 4.3: Assembly language shall be encapsulated and isolated.
_Ref 4.3.1_
- AArch64 port files (portable/GCC/ARM_AARCH64_ARMV9/) use inline assembly
to access system registers (GIC, generic timer, PAC keys, MTE, SVE
configuration) that have no C-language equivalent. Assembly is confined to
the port layer and isolated from application code.
#### Dir 4.7
MISRA C:2012 Dir 4.7: If a function returns error information, then that error
@ -116,6 +126,31 @@ _Ref 11.5.5_
because data storage buffers are implemented as uint8_t arrays for the
ease of sizing, alignment and access.
#### Rule 5.8
MISRA C:2012 Rule 5.8: Identifiers that define objects or functions with
external linkage shall be unique.
_Ref 5.8.1_
- The Armv9 port (portable/GCC/ARM_AARCH64_ARMV9/portmacro.h) defines macros
that redirect `pvPortMalloc` and `vPortFree` to MTE-tagged wrapper functions
when `configARMV9_MTE_HEAP == 1`. This keeps MTE heap tagging logic isolated
in the port without modifying shared upstream kernel files. An alternative
that eliminates this deviation (integrating tagging into heap_4.c) is
documented in the source.
#### Rule 11.6
MISRA C:2012 Rule 11.6: A cast shall not be performed between a pointer to void
and an arithmetic type.
_Ref 11.6.1_
- The Armv9 MTE port (portable/GCC/ARM_AARCH64_ARMV9/mte_port.c) casts
between pointer and uintptr_t to strip the MTE tag bits (top byte) from
tagged pointers before passing them to the underlying allocator. This is
required because MTE tags are encoded in pointer bits 56-59 and must be
removed to recover the canonical address.
#### Rule 14.3
MISRA C-2012 Rule 14.3: Controlling expressions shall not be invariant.