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MON 272B (octal) — DeletePage (DELPG)

Deletes the pages of an opened file between two page numbers (FirstPage..LastPage inclusive; LastPage = −1 means to end of file) and returns the number of pages deleted.

Status: dispatch head byte-proven as a fall-through (GOTAB[272B] = 000000); worker body is real SINTRAN L bytes; the exact MON 272 → worker link crosses an uncarved kernel bridge (CALLPROC/MFELL) — see Honest caveats. All addresses/values are octal.

Dispatch path

flowchart LR
    A["User program<br/>MON 272B"] --> B["ENT14 level-14<br/>T = MON number"]
    B --> C["GOTAB[272B] = 000000<br/>(fall-through, byte proven)"]
    C -.uncarved CALLPROC/MFELL.-> E["DELPG delete worker<br/>006-S3FS :110472B"]
    E --> F["page-table free<br/>via JPL I workers"]
    class A blue
    class B,C teal
    class E,F 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

GOTAB[272B] is literally 000000, so there is no entry stub to disassemble; the dashed hop (C ⇢ E) is the resident CALLPROC/MFELL second-level dispatch, which is not present in any carved segment and cannot be followed statically.

Code location (dispatch path)

Every row is a real region you can open. Byte offset = (addr − loadbase) in octal words × 2.

Role Segment (full disasm) Addr range (octal) Byte offset Symbol Verdict
GOTAB[272] dispatch word commoncode.asm · .hex 071525B (1 word) 59050 GOTAB+272 = 000000 VERIFIED (fall-through)
resident CALLPROC/MFELL bridge — (uncarved) — — CALLPROC UNVERIFIED
DELPG delete worker body 006-S3FS.asm · .hex 110472B–111012B 51828 DELPG real bytes; link UNVERIFIED

Verify by hand: grep '^110472 ' ../../segments-ref/006-S3FS/006-S3FS.hex → byte offset 51828; then dd if=../../../segments/006-S3FS.bin bs=1 skip=51828 count=4 | od -An -tx1 → 22 4e cc 65 (the stored words 021116 146145 = STD I 116 / RADD CLD SL DA, the DELPG prologue). Confirm the fall-through: dd if=../../../resident/SINTRAN-DATA_commoncode.bin bs=1 skip=59050 count=2 | od -An -tx1 → 00 00; prove-mon.py 272 reads GOTAB[272] … 000000.

Instruction walkthrough

Full listing: 272B-DeletePage.ASM. There is no entry stub (fall-through dispatch); the body is the DELPG worker.

Prologue (110472–110476) saves the caller A:D pair (110472 STD I 116) and calls resident register-save SPUSH via pointer @110611 = 003752B. File lookup (110477–110501) resolves the open-file descriptor from the caller file number via pointer @110613 = 010376B. Descriptor + access checks (110502–110537) test the descriptor for null (110504 SKP IF DX EQL 0 → error 110507 SAA 132 / 110511 SAA 125), scan attribute bits (110513 LDA ,X 3, masked BSKP → SAA 133/125) and set up the page range (110524–110537 JPL I 66/60 → @110616); all fault paths take an indirect exit → @110614. Range bound (110540–110606) computes LastPage − FirstPage as a 32-bit value (110576 RSUB SX DD / 110577 RADD ADC / 110601 RSUB ST DA); 110602 JAP errors (SAA 174) on a negative range. Delete loop (110624–111002) locates each page in the file's page-table entry (compares against the ,X 27 / ,X 51 slot lists), frees the mapping (110647/110650 STZ ,X 0 / STZ ,X 1), marks the table word dirty (110653/110674 BSET ONE … DT / STT ,X 7), commits it (110700 JPL I 110 → @111010), and bumps the 32-bit deleted count (,B 15) and current page (,B 7), looping while pages remain (110721 JAN → 110723). Result + return (110723–110760) stores the 32-bit deleted count into the caller frame (110737 STD ,X 23) and returns via 110760 JMP I 32 (@111012 = 003776B, SPOP). Pointer/data tables (110610–110623, 111005–111012) hold the JPL I targets.

Parameter / register contract

Manual-side names/types are from 272B_DeletePage.yaml (MAC: LDT FILNO / LDA (FIRST / LDX (LAST / MON 272 / STD NODEL).

Reg / field Dir Meaning Verdict
T = FileNo in open-file number, resolved at 110477–110501 inferred (manual)
A = FirstPage in address of the 32-bit first page to delete inferred (manual)
X = LastPage in address of the 32-bit last page (−1 = to end of file) inferred (manual)
range check internal LastPage − FirstPage (32-bit) at 110576–110601; negative → error 174 VERIFIED (bytes)
D = NoOfPages out number of pages deleted (double word), stored at 110737 VERIFIED stored; meaning inferred
error return out standard error code on the fault paths inferred (manual)

This post-CALLPROC body works through ,B frame fields, so the precise T/A/X mapping is inferred from the manual and the caller-side MON 272 wrapper, not byte-proven here.

Pseudo-code (for an emulator)

See 272B-DeletePage.pseudo.c — a pseudo-C model of the handler for emulator authors. Control flow, the 32-bit range check and the page-free loop shape are byte-verified; the page-table/free-space worker semantics are inferred from the call structure. Every instruction is translated per the canonical ND-100 Instruction Semantics reference.

Honest caveats

What is byte-proven: GOTAB[272B] = 000000 (a fall-through, matching prove-mon.py 272); the DELPG worker at 110472B is real code (its SPUSH/SPOP prologue/epilogue, its open-file lookup, its 32-bit LastPage − FirstPage range check, its page-table clearing loop, and its 32-bit deleted-count result at 110737).

What is NOT proven: the link from the MON number to the DELPG worker. Because GOTAB[272] = 000000 there is no static edge from the level-14 dispatch word into 110472B; the only path runs through the resident CALLPROC/MFELL second-level dispatch, in an uncarved overlay. So the MON 272 → DELPG attribution rests on the symbol name (DELPG = DELete PaGe) + the matching delete behaviour, not a followed pointer — UNVERIFIED in the strict sense. This reconciles into one story: the body is genuine SINTRAN L bytes (its direct branches all close inside the carve, up to its pointer tables), but the attachment to MON 272 is runtime-populated. Confirming it needs a live trace: break at the level-14 MON entry with the number = 272, single-step the resident fall-through, and confirm P lands on DELPG = 110472B.

Method: ../../../../../EXTRACTING-RESIDENT-CODE.md §9 · dispatch reality: ../../TASK-05-mismatches.md §G · master map: ../../MON-CALL-INDEX.md.