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MON 322B (octal) - GSGNO (GetSegmentNo)

Given a segment name (6 characters), return that segment's number. Segment names are created by the RT LOADER or when a program is dumped reentrant (@DUMP-PROGRAM-REENTRANT). ND-100 monitor call.

Status: byte-verified (dispatch + worker body). The worker is real carved code in 003-S3CP, with siblings GRTDA / 1FU7. All addresses/values are octal.

CORRECTED 2026-07-13. The previous version of this folder located the worker via a fictional level-14 GOTAB/DSI7 compiler stub and read GSGNO from SINTRAN-DATA_commoncode. MON calls are not dispatched through that GOTAB (it is MFELL for 224 of 256 calls); they go through MCTAB @ 005620B (segment 044-S3IDPIT). MCTAB[322B] = 041424B = GSGNO, and that worker is carved in 003-S3CP. See ../317B-ExecuteCommand/README.md and SINTRAN/CARVING-HANDOFF.md section 3a.

Dispatch path

flowchart LR
    A["User program<br/>MON 322B"] --> B["ENT14 level-14<br/>026-S3IMPIT :072167B"]
    B --> C["GOTAB[322B] = MFELL<br/>:071555B"]
    C --> D["MFELL level switch<br/>:072114B -> CALLP 032201B"]
    D --> E["MCTAB[322B] = GSGNO<br/>044-S3IDPIT :006142B = 041424B"]
    E --> F["GSGNO worker<br/>003-S3CP :041424B"]
    class A blue
    class B,C,D,E teal
    class 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

Code location (dispatch path)

Byte offset = (addr - loadbase) in octal words x 2 (decimal). Offsets reproduced with dd.

Role Segment Addr (octal) Byte offset Symbol Verdict
MCTAB[322B] slot 044-S3IDPIT.asm 006142B = 041424B 2244 -> GSGNO VERIFIED
GSGNO worker body 003-S3CP.asm 041424B-041447B 9768 GSGNO VERIFIED

Verify by hand (from tools/sintran-segment-carver/versions/L-VSX-500/segments/): 

dd if=044-S3IDPIT.bin bs=1 skip=2244 count=2 | od -An -tx1   ->  43 14   (= 041424B = GSGNO)
dd if=003-S3CP.bin    bs=1 skip=9768 count=2 | od -An -tx1   ->  ba 16   (= 135026B, GSGNO entry)

Instruction walkthrough

Full listing: 322B-GetSegmentNo.ASM.

GSGNO calls a helper (JPL I 26) that looks up the segment by name, re-enables interrupts (ION), then stages the argument words (,B -200 / -177 / -176) and calls two more helpers. If the second helper reports not-found it takes the error return (JMP I ,B -36 -> 041376B). Otherwise it enters an IOF-guarded critical section (041436B), walks a segment table at mem[036], matches the name, and returns the segment number via ION + JMP I ,B -36 -> 041411B. The helper calls, the critical section and the two-way return are byte-proven; the exact name-match detail is inferred.

Parameter / register contract

Reg / field Dir Meaning Verdict
mem[,B -200/-177/-176] in staged argument words (segment name / key) VERIFIED (bytes)
segment table mem[036] in table walked under IOF to find the match VERIFIED (bytes); layout inferred
result (A) out segment number on the normal return; error return if not found VERIFIED (two-way return); value inferred
segment name (6 chars) in manual: the name to resolve inferred (manual)

Pseudo-code (for an emulator)

See 322B-GetSegmentNo.pseudo.c - the helper lookups, the IOF/ION critical section and the found/not-found return are byte-verified; the name-match detail is inferred.

Honest caveats

What is byte-proven: MCTAB[322B] = 041424B = GSGNO; the GSGNO entry bytes at 041424B in 003-S3CP match the disassembly; the routine resolves a segment via helper lookups and an IOF-guarded table walk, and has distinct found / not-found returns.

What is NOT proven: the exact 6-character name comparison and the layout of the segment table at mem[036]. The old "DSI7 stub + commoncode worker" model was the wrong dispatch table/overlay and is withdrawn.

Method: ../../../../../EXTRACTING-RESIDENT-CODE.md · master map: ../../MON-CALL-INDEX.md.