FA-89697 / Instruction set emulation / Member archive

Directory accessed bit not set · case 02

After a walk the directory entry still reads as unaccessed.

Member previewVariant 2 · 3 implementations · 9 checks per implementation

Case contract

Input [va, write, user, root, mem]; mem maps decimal-string physical addresses to 32-bit entries (missing = 0). VA splits 10/10/12 (directory index va>>22, table index (va>>12)&0x3FF, offset). The PDE is at root + 4*dir, the PTE at (PDE frame << 12) + 4*table. Bits: P=1, W=2, U=4, A=32, D=64; frame = entry >> 12. Not present -> ['fault', err]; write without W on both levels or user access without U on both levels -> ['fault', err | 1], where err = 2 if write plus 4 if user. On success set A on both entries and D on the PTE only for writes, returning ['ok', physical address, sorted [address, entry] of memory].

Why this case matters

MMU emulation must combine permissions across levels and update accessed/dirty bits exactly as guest operating systems expect.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
user read of user page	`["ok", 21003, [["4100", 8199], ["4104", 12289], ["8204", 20519], ["8208", 24577], ["10252", 32775], ["12288", 28679], ["12292", 36869]]]`	`["ok", 21003, [["4100", 8231], ["4104", 12289], ["8204", 20519], ["8208", 24577], ["10252", 32775], ["12288", 28679], ["12292", 36869]]]`	Failed

MEMBER ARCHIVE

The complete case is available to members.

This record includes three runnable implementations, regression fixtures, execution results, and source hashes.

Member access is invitation-based. Sign in with your invited account to inspect the sources.