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MON 237B (octal) - SetFileAccess (SFACC)

Sets the access protection of a file - the public (other-user) access, the friend access, and the owner's own access - each expressed as a combination of the characters R W A C D N. You need directory access to the file to change it; user SYSTEM and RT may set the access on any file.

Status: GOTAB dispatch head byte-proven as fall-through (GOTAB[237B] = 000000, no per-call stub); the SFACC worker is real SINTRAN L bytes - the MODE-3 entry of a shared create/allocate/access/expand dispatcher whose body lives at 105564B. The exact MON 237 -> worker link crosses an uncarved kernel bridge (see Honest caveats). All addresses/values are octal.

Dispatch path

flowchart LR
    A["User program<br/>MON 237B"] --> B["ENT14 level-14<br/>T = MON number"]
    B --> C["GOTAB[237B] = 000000<br/>(byte-proven: fall-through)"]
    C -.uncarved MFELL / CALLPROC.-> D["SFACC entry<br/>006-S3FS :105552B<br/>SSM=1 SSK=1 = mode 3"]
    D --> E["shared create/alloc/access/expand<br/>dispatcher body<br/>006-S3FS :105564B"]
    class A blue
    class B,C blue
    class D teal
    class E green
    classDef blue fill:#E3F2FD,stroke:#0D47A1,color:#0D47A1
    classDef teal fill:#E0F7FA,stroke:#00838F,color:#00838F
    classDef green fill:#E8F5E9,stroke:#2E7D32,color:#2E7D32

The GOTAB slot is zero, so there is no per-call entry stub. The dashed hop (C -> D) is the resident MFELL/CALLPROC fall-through second-level dispatch - not present in any carved segment. SFACC is the mode-3 arm of a shared body it enters by setting two STS flags (SSM, SSK) that the body reads back into a 2-bit mode word.

Code location (dispatch path)

Every row is a real region you can open. Byte offset is the 006-S3FS.hex byte offset.

Role Segment (full disasm) Addr range (octal) Byte offset Symbol Verdict
GOTAB[237] dispatch word commoncode.asm - .hex 071472B (1 word) 58996 GOTAB+237 = 000000 VERIFIED (fall-through)
resident MFELL/CALLPROC bridge - (uncarved) - - CALLPROC UNVERIFIED
SFACC mode-3 entry 006-S3FS.asm - .hex 105552B-105554B (3w) 48852 SFACC real bytes; link MISATTRIBUTED
shared dispatcher body 006-S3FS.asm - .hex 105564B-106042B (175w) 48872 (shared) real bytes - VERIFIED

Verify by hand: grep '^105552 ' ../../segments-ref/006-S3FS/006-S3FS.hex -> byte offset 48852; then dd if=../../../segments/006-S3FS.bin bs=1 skip=48852 count=6 | od -An -tx1 -> f8 b8 f8 90 a8 08 (= octal 174270 174220 124010 = BSET ONE SSM / BSET ONE SSK / JMP 10, the SFACC mode-3 entry).

The GOTAB slot itself: dd if=../../../resident/SINTRAN-DATA_commoncode.bin bs=1 skip=58996 count=2 | od -An -tx1 -> 00 00 (= 000000, fall-through).

Instruction walkthrough

Full listing: 237B-SetFileAccess.ASM. There is no F16xx/F17xx stub because GOTAB[237] = 0.

Mode-select entry (105552-105554) - SFACC sets SSM (STS bit7 M) and SSK (STS bit2 K) both to 1, then 105554 JMP 10 merges into the shared body at 105564. The three sibling entries in the same cluster set different flag pairs: EXPFI (105555, mode 2, ExpandFile/231B), CRALN (105560, mode 1, NewFileVersion/253B), CRALF (105562, mode 0).

Prologue + mode rebuild (105564-105574) - 105564 STD I 77 stashes the caller's parameter double-word; 105567 SAB 145 builds the 145-word frame; 105570 JPL I 74 -> 003752 is the shared resident prologue. Then the two STS flags are rebuilt into a 2-bit mode word: 105571 RADD CLD 0 DA clears A, 105572 SHA LIN 2 shifts left pulling the M bit into the vacated position, 105573 BSET BAC 0 DA sets bit0 to the K accumulator, and 105574 STA ,B 123 stores MODE = (M<<1) | K (so SFACC = 3).

Parameter marshalling (105575-105621) - the caller's four string pointers (file name, public/friend/own access) are copied / address-adjusted into the local frame (B+135..B+144); 105625 JPL I 51 -> 031075 parses the file name.

Mode dispatch (105627-105662) - 105627 LDA ,B 123 / 105630 SAT 3 / 105631 SKP IF DA LST ST splits mode 3 (SetFileAccess, 105633+) from the create / allocate / expand arms (mode < 3, 105641+). The mode-3 arm applies the access words via 105636 JPL I 41 -> 031067.

Finish (105777-106042) - 105777 MIN ,B 4 bumps the success flag; the epilogue restores the caller words (106000-106005) and returns through 106007 JMP I 33 -> 106042 = 003776. Error paths funnel through 106010 STA ,B 2 (status -> caller B+2) into the same teardown without the bump.

Parameter / register contract

Reg / field Dir Meaning Verdict
entry point in 105552B = SFACC mode-3 entry (fall-through, no stub) VERIFIED (bytes)
STS M / K internal set by SFACC to select mode 3 (BSET ONE SSM/SSK) VERIFIED (bytes)
X (manual) in address of the file-name string inferred (manual MAC example)
T (manual) in address of the public-access string inferred (manual MAC example)
A/D (manual) in addresses of the own-access and friend-access strings inferred (manual MAC example)
local frame B internal SAB 145 = 145-word working frame VERIFIED (bytes)
B+123 internal 2-bit MODE word (M<<1)|K (STA ,B 123 at 105574) VERIFIED (bytes)
B+135/136/137 internal public / friend / own access buffers VERIFIED (bytes); role inferred
B+2 out returned status word (STA ,B 2 at 106010) VERIFIED (bytes)

The user-visible X/T/A/D string-pointer convention lives in the caller-side MON 237 wrapper and the uncarved MFELL/CALLPROC frame, so the precise register-to-string assignment is inferred from the manual (237B_SetFileAccess.yaml), not byte-proven here.

Pseudo-code (for an emulator)

See 237B-SetFileAccess.pseudo.c - a pseudo-C model of the handler for emulator authors. The mode-select entry, the STS-flag mode rebuild, control flow, and the mode dispatch are byte-verified; the access-string roles and the identity of the per-mode primitives are inferred.

Every instruction in the model is translated per the canonical ND100-INSTRUCTION-SEMANTICS.md (BSET/BSKP on STS bits M/K; SHA LIN M-bit fill (emulator-authoritative); BSET BAC 0 DA = bit0 from K (emulator-authoritative); SKP IF DA LST ST signed less-than; MIN ,B 4 success bump).

Honest caveats

What is byte-proven: GOTAB[237B] = 000000 (level-14 dispatch, a fall-through with no per-call vector); the SFACC entry at 105552B in 006-S3FS is real code (entry bytes 174270 174220 124010 match the disassembly); it sets the M and K STS flags to 1 and joins the shared body at 105564B, which rebuilds those flags into the 2-bit mode word (M<<1)|K = 3 and dispatches on it.

What is NOT proven: the link from the zero GOTAB slot to the SFACC entry. Because the vector is zero there is no stub to disassemble and no pointer to dereference; dispatch drops into the resident MFELL/CALLPROC path in an uncarved overlay. So the MON 237 -> SFACC attribution rests on the SFACC symbol name (SetFileAccess), the mode-3 flag pattern, and the matching four-string contract, not a followed pointer - hence MISATTRIBUTED in the strict sense.

Shared body: SFACC (237B), EXPFI (231B), CRALN (253B) and CRALF all enter the same dispatcher at 105564B differing only in the two STS flags; this is why the ASM and pseudo-C for 237B and 253B share the body and differ only in the entry. The mode-<3 sub-blocks (105700-105776) handle the create / allocate variants and are modelled only at the spine.

Region bound: the shared body is bounded to the next symbol SETTF = 106043B; its control flow closes on the 003776 resident-return link cell at 106042. Several link-cell contents (031067, 031075) match no FILSYS-SYMBOLS entry.

Method: ../../../../../EXTRACTING-RESIDENT-CODE.md - dispatch reality: ../../TASK-05-mismatches.md - master map: ../../MON-CALL-INDEX.md.