[Bug] Misaligned MMIO access inaccurately raises AddrMisaligned instead of AccessFault

[oChunCai]

Describe the bug

isa_mmio_misalign_data_addr_check() in src/memory/paddr.c raises EX_LAM/EX_SAM for misaligned accesses to MMIO regions. RISC-V Privileged Spec §3.6.1 non-idempotent regions should raise *AccessFault instead, to prevent OS trap handlers from emulating the access via multiple smaller MMIO accesses.

This is the NEMU-side counterpart of XiangShan #5695.

Expected behavior

Misaligned access to MMIO → EX_LAF (load) / EX_SAF (store), consistent with spec recommendation:

Non-idempotent regions might not support misaligned accesses. Misaligned accesses to such regions should raise access-fault exceptions rather than address-misaligned exceptions.

Code location

src/memory/paddr.c:173:

int ex = cpu.amo || type == MEM_TYPE_WRITE ? EX_SAM : EX_LAM;  // should be EX_SAF / EX_LAF

Necessary information on versions

• NEMU version: master branch