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MON 252B (octal) - BackupClose (BCLOS)

Closes a file, but - unlike ordinary CloseFile (43B) - leaves the version number and the last-accessed date unchanged, and does not affect the page count of temporary or spooling files. Mainly used by the BACKUP-SYSTEM.

Status: GOTAB dispatch head byte-proven non-zero (GOTAB[252B] = 066252B), landing on the resident F1733 dispatch-stub cluster in the 025-S3IRPIT RPIT image; the functional worker BCLOS (real SINTRAN L bytes in 006-S3FS) is one entry of a shared close dispatcher that calls the file-close primitive FCLOS - the same primitive CLOSF (MON 43B) calls. The stub holds no static pointer to BCLOS, so the stub -> worker hop crosses an uncarved kernel bridge - hence MISATTRIBUTED (see Honest caveats). All addresses/values are octal.

Dispatch path

flowchart LR
    A["User program<br/>MON 252B"] --> B["ENT14 level-14<br/>T = MON number"]
    B --> C["GOTAB[252B] = 066252B<br/>(byte-proven: non-zero)"]
    C --> D["F1733 dispatch stub<br/>025-S3IRPIT :066252B<br/>(RPIT image)"]
    D -.uncarved CALLPROC.-> E["BCLOS entry<br/>006-S3FS :103350B<br/>shared close body 103357B"]
    E --> F["FCLOS file-close primitive<br/>006-S3FS :067612B"]
    class A blue
    class B,C blue
    class D 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[252B] is non-zero: it points at symbol F1733 in the resident RPIT image 025-S3IRPIT, part of the same F17xx GOTAB-stub cluster used by MON 236B (F1725) and MON 254B (F1734). The stub is real resident code but a fragment (it continues past the next symbol F1735=066256B); it does not statically reference BCLOS, so the dashed D -> E hop is the uncarved resident CALLPROC bridge.

Code location (dispatch path)

Every row is a real region you can open. Byte offset is the segment .hex byte offset.

Role Segment (full disasm) Addr range (octal) Byte offset Symbol Verdict
GOTAB[252] dispatch word commoncode.asm - .hex 071505B (1 word) 59018 GOTAB+252 = 066252 VERIFIED (non-zero)
F1733 dispatch stub (fragment) 025-S3IRPIT.asm - .hex 066252B-066255B (4w, to F1735) 29012 F1733 real bytes; link UNVERIFIED
resident CALLPROC bridge - (uncarved) - - CALLPROC UNVERIFIED
BCLOS entry + shared close body 006-S3FS.asm - .hex 103350B-103416B (47w) 46544 BCLOS real bytes; link MISATTRIBUTED
FCLOS file-close primitive 006-S3FS.asm - .hex 067612B (call target) - FCLOS called by CLOFI arm (link cell 103415) - VERIFIED

Verify by hand: grep '^103350 ' ../../segments-ref/006-S3FS/006-S3FS.hex -> byte offset 46544; then dd if=../../../segments/006-S3FS.bin bs=1 skip=46544 count=8 | od -An -tx1 -> f8 38 f8 90 a8 05 f8 b8 (= octal 174070 174220 124005 174270 = BSET ZRO SSM / BSET ONE SSK / JMP 5 / BSET ONE SSM (SPERM), the BCLOS entry cluster).

The GOTAB slot itself: dd if=../../../resident/SINTRAN-DATA_commoncode.bin bs=1 skip=59018 count=2 | od -An -tx1 -> 6c aa (= 066252, the F1733 stub address).

The stub bytes: grep '^66252 ' ../../segments-ref/025-S3IRPIT/025-S3IRPIT.hex -> byte offset 29012; then dd if=../../../segments/025-S3IRPIT.bin bs=1 skip=29012 count=8 | od -An -tx1 -> 0c fe 49 12 0c ff 4c fc.

Instruction walkthrough

Full listing: 252B-BackupClose.ASM.

F1733 stub fragment (066252-066255) - STA ,X -2 / LDA ,B 22 / STA ,X -1 / LDA ,X -4, real bytes in the RPIT image; a fragment of resident dispatch code that continues past the next symbol F1735=066256B (uncarved). It does not statically reference BCLOS.

Mode-select entry (103350-103356) - BCLOS clears SSM (STS bit7 M) and sets SSK (STS bit2 K), then 103352 JMP 5 merges into the shared close body at 103357. The cluster siblings are SPERM (103353, sets SSM - permanent-close variant) and CLOFI (103355, clears both - plain close).

Prologue (103357-103364) - 103357 STD I 31 stashes the caller's double-word (file number + modified flag); 103362 SAB 6 builds a small 6-word local frame; 103363 JPL I 26 -> 003752 prologue; 103364 STT I 26 records the file number.

Mode dispatch (103365-103402) - 103365 BSKP ONE SSM selects the permanent path (103370 JPL I 23 -> 072465 = SETPO, the MON 236B worker); 103373 BSKP ONE SSK selects the BackupClose path (103375 LDA ,B 2 reads the modified flag, then 103376 JPL I 16 -> 067602 closes without touching the version/date); the neither-flag CLOFI path calls the plain file-close primitive 103401 JPL I 14 -> 067612 = FCLOS. The call to FCLOS - the same primitive CLOSF (MON 43B) reaches - is the byte-level proof that BCLOS is a close-family worker.

Finish (103403-103416) - 103403 MIN ,B 4 bumps the success flag; 103405 JMP I 11 -> 103416 = 003776 is the resident return. The error path 103406 STA ,B 2 stores the status word into caller slot B+2 and falls to the teardown without the bump. Words 103410-103416 are a pointer table (link cells: 003752, 072465, 067602, 067612, 003776).

Parameter / register contract

Reg / field Dir Meaning Verdict
GOTAB[252] in 066252B = F1733 dispatch stub (non-zero vector) VERIFIED (bytes)
worker entry in 103350B = BCLOS entry (clears SSM, sets SSK) VERIFIED (bytes)
T (manual) in file number returned from an earlier open inferred (manual MAC example)
A (manual) in modified flag (0 = not marked modified) inferred (manual MAC example)
frame B+2 in modified flag, loaded by LDA ,B 2 at 103375 VERIFIED (bytes); role inferred
local frame B internal SAB 6 = 6-word working frame VERIFIED (bytes)
FCLOS 067612 out file-close primitive (JPL I 14 at 103401) VERIFIED (bytes)
B+2 out returned status word (STA ,B 2 at 103406) VERIFIED (bytes)

The user-visible T = file-number, A = flag convention lives in the caller-side MON 252 wrapper; the manual shows LDT FILNO / LDA FLAG / MON 252, matching the worker's STT I 26 and LDA ,B 2. The two-parameter contract is from the 252B_BACKUPCLOSE.yaml parameter contract.

Pseudo-code (for an emulator)

See 252B-BackupClose.pseudo.c - a pseudo-C model of the handler for emulator authors. The mode-select entry, control flow, and the three-way close dispatch (SETPO / backup-with-flag / FCLOS) are byte-verified; the modified-flag role and the skip-return polarity are inferred.

Every instruction in the model is translated per the canonical ND100-INSTRUCTION-SEMANTICS.md (BSET/BSKP on STS bits M/K; STD I/STT I indirect stores; RADD CLD register copy; MIN ,B 4 success bump).

Honest caveats

What is byte-proven: GOTAB[252B] = 066252B (level-14 dispatch, a non-zero vector into the 025-S3IRPIT RPIT image - matching the F17xx stub cluster); the BCLOS entry at 103350B in 006-S3FS is real code (entry cluster bytes 174070 174220 124005 174270 match the disassembly); it joins the shared close body at 103357B which calls the file-close primitive FCLOS (067612B, link cell 103415) - the same primitive the ordinary CloseFile worker uses.

What is NOT proven: the F1733 stub does not contain a static pointer to BCLOS; the stub is a fragment of resident dispatch code in the relocated RPIT image whose control flow continues past F1735 into uncarved resident code. So the stub -> BCLOS link goes through the resident CALLPROC bridge (uncarved) - the MON 252 -> BCLOS attribution rests on the BCLOS symbol name, its FCLOS call, and the matching file-number+flag contract, not a followed pointer - hence MISATTRIBUTED in the strict sense. Confirming the link needs a live trace: issue a real MON 252 on an open file, single-step the level-14 dispatch through F1733 and the resident CALLPROC, and confirm P lands on BCLOS = 103350.

Shared close body: BCLOS (BackupClose), SPERM (permanent-close) and CLOFI (plain close) all enter the same body at 103357B, differing only in the two STS flags; the flags steer the dispatch to SETPO (072465), the backup-with-flag close (067602), or FCLOS (067612) respectively.

Region bound: the shared body is bounded to the next symbol SETUP = 103417B; its control flow closes on the 003776 resident-return link cell at 103416.

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