MON 257B (octal) - OpenFileInfo (FOPEN)¶
CORRECTED 2026-07-15 (byte-verified). The worker + dispatch described below are on the DEBUNKED model and are WRONG. Byte truth from the carved L07 image:
MCTAB[257B] = 006077B = FOPFN=111212Bin segment 006-S3FS, reached by the real dispatchMON 257B -> ENT14(072167B) -> GOTAB[257B]=MFELL(072114B) -> CALLP(032201B) -> MCTAB[257B]=FOPFN. Any "GOTAB from commoncode" / "uncarved CALLPROC bridge" / "F16xx stub" / old worker name below is an artefact of the wrong table. Verified:dd if=044-S3IDPIT.bin bs=1 skip=2174 count=2->92 8a. Cross-ref ../317B-ExecuteCommand/README.md and SINTRAN/CARVING-HANDOFF.md sec 3a.
Gets information about an already-open file. The caller supplies a file name and a default file type; on the normal return the call delivers the open file number and the access type (and, for a peripheral file, the logical device number). The file must already have been opened (e.g. with MON 50B OpenFile).
Status: GOTAB dispatch head byte-proven as fall-through (GOTAB[257B] = 000000,
no per-call stub); the FOPEN worker body is real SINTRAN L bytes and calls the
FCON file-system connect/context helper; the exact MON 257 -> worker link
crosses an uncarved kernel bridge (see Honest caveats). All
addresses/values are octal.
- Full disassembly:
257B-OpenFileInfo.ASM- the actual code (the FOPEN worker body; there is no entry stub because the GOTAB slot is zero). - Bytes live once in the canonical segment layer:
../../segments-ref/.
Dispatch path¶
flowchart LR
A["User program<br/>MON 257B"] --> B["ENT14 level-14<br/>T = MON number"]
B --> C["GOTAB[257B] = 000000<br/>(byte-proven: fall-through)"]
C -.uncarved MFELL / CALLPROC.-> E["FOPEN open-file-info worker<br/>006-S3FS :67432B"]
E --> F["FCON connect/context helper<br/>006-S3FS :67002B"]
class A blue
class B,C blue
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:#2E7D32The GOTAB slot is zero, so there is no per-call entry stub. The dashed hop
(C -> E) is the resident MFELL/CALLPROC fall-through second-level dispatch -
it is not present in any carved segment, so it is the one link that cannot be
followed statically.
Code location (dispatch path)¶
Every row is a real region you can open. Byte offset = (addr - loadbase) in octal words x 2.
| Role | Segment (full disasm) | Addr range (octal) | Byte offset | Symbol | Verdict |
|---|---|---|---|---|---|
| GOTAB[257] dispatch word | commoncode.asm - .hex | 071512B (1 word) |
59028 | GOTAB+257 = 000000 |
VERIFIED (fall-through) |
| resident MFELL/CALLPROC bridge | - (uncarved) | - | - | CALLPROC |
UNVERIFIED |
| FOPEN open-file-info worker body | 006-S3FS.asm - .hex | 67432B-67571B (96w) |
34356 | FOPEN |
real bytes; link MISATTRIBUTED |
| FCON connect/context helper | 006-S3FS.asm - .hex | 67002B (call target) |
33796 | FCON |
called by FOPEN (link cell 67565) - VERIFIED |
Verify by hand: grep '^67432 ' ../../segments-ref/006-S3FS/006-S3FS.hex -> byte offset 34356;
then dd if=../../../segments/006-S3FS.bin bs=1 skip=34356 count=8 | od -An -tx1 -> 22 57 cc 65 cc 59 f0 06
(= octal 021127 146145 146131 170006 = STD I 127 / RADD CLD SL DA / RADD CLD SB DD / SAB 6, the FOPEN entry).
The GOTAB slot itself:
dd if=../../../resident/SINTRAN-DATA_commoncode.bin bs=1 skip=59028 count=2 | od -An -tx1 -> 00 00 (= 000000, fall-through).
Instruction walkthrough¶
Full listing: 257B-OpenFileInfo.ASM. The functional body
is the FOPEN worker (region B); there is no F16xx stub because GOTAB[257] = 0.
All calls to shared workers are indirect (JPL I / JMP I) through a table
of pointer words at the tail of the window (67561-67571). nd100-dis renders
those pointer words as bogus instructions (ROP NOOP, STZ I ..., SUB I ...) -
they are data (link cells), not code; their contents are the real worker
addresses (resolved below).
Entry prologue (67432-67436) - 67432 STD I 127 stashes the caller's
double-word parameter; 67435 SAB 6 builds a small local frame B (6 words);
67436 JPL I 124 -> 003752 is the shared resident prologue worker (the same
prologue cell used by the file open / read / write bodies).
Open-file-table scan (67442-67456) - 67442 LDA ,X 0 reads the current
open-file-table entry; 67445 JAZ 12 -> 67457 breaks out on an empty/matching
slot; 67450 SKP IF DX EQL ST / 67451 JMP 4 compares the entry; 67456 JMP -14
-> 67442 loops to the next entry (67446 AAX 2). On table exhaustion,
67452 SAA 122 loads error 122 and exits via 67453 JMP 104 -> 67557.
Resolve + extract (67457-67551) - 67457-67461 fetch the caller's
name/type arguments (LDT ,B 1, LDA ,B 2, LDX ,B 0); 67462 JPL I 103 ->
067002 (FCON, the file-system connect/context helper) resolves the file
context. The two branches at 67504-67525 and 67526-67551 walk the file
descriptor and build the returned file-number / access-code / device-number
group, each writing the result code SAA 120 and storing it with STA ,B 2.
Exit (67552-67560) - 67553/67557 STA ,B 2 write the result word into the
caller's status slot B+2; every path funnels into the resident return
67555/67556 JMP I 13 -> 003776.
The JPL I 103 call to FCON (link cell 67565 = 067002) is the byte-level
proof that FOPEN drives the file-system open-file lookup. FOPEN = 67432B was
selected because it is the FILSYS symbol the OpenFileInfo anchor points at, and it
carries the canonical file-worker prologue (STD I / SAB / JPL I -> 003752,
identical in shape to the OpenFile and read/write worker entries).
Parameter / register contract¶
| Reg / field | Dir | Meaning | Verdict |
|---|---|---|---|
| entry point | in | 67432B = FOPEN worker entry (fall-through, no stub) |
VERIFIED (bytes) |
D (double) |
in | caller parameter block, saved first (STD I 127) |
VERIFIED (copy); layout inferred |
local frame B |
internal | SAB 6 = 6-word working frame |
VERIFIED (bytes) |
X (manual) |
in | address of file-name string | inferred (manual MAC example) |
A (manual) |
in | address of default file-type string | inferred (manual MAC example) |
T (manual) |
out | open file number | inferred (manual: STT FILNO) |
A (manual) |
out | access code (0 read, 1 write, 2 read+write) | inferred (manual: STA ACODE) |
D (manual) |
out | logical device number (peripheral files) | inferred (manual: COPY SD DA) |
B+2 |
out | returned status word (STA ,B 2 at 67523/67553/67557) |
VERIFIED (bytes) |
error 122 |
out | table-exhausted / not-found literal (SAA 122 at 67452) |
VERIFIED (bytes); mapping inferred |
result 120 |
out | result/access literal (SAA 120 at 67522/67545) |
VERIFIED (bytes); mapping inferred |
The user-visible X/A/T/D register convention lives in the caller-side
MON 257 wrapper and the uncarved MFELL/CALLPROC frame, so the precise
user-register-to-field assignment is inferred from the manual, not
byte-proven here. The error/result literals 122/120 are VERIFIED in the code;
their mapping to the SINTRAN error/access tables is UNVERIFIED.
Pseudo-code (for an emulator)¶
See 257B-OpenFileInfo.pseudo.c - a pseudo-C
model of the handler for emulator authors. Control flow + the open-file-table
scan + the call to the FCON helper are byte-verified; the parameter-field
semantics and error-number meanings are inferred from the call structure and the
manual.
Every instruction in the .pseudo.c is translated against the canonical
ND100-INSTRUCTION-SEMANTICS.md
(bare LDx/LDT/AND disp = P-relative mem[P+disp], not literals; SKP/BSKP skip
polarity; RADD CLD SD DA = A = D; T/X transfers = physical EL).
Honest caveats¶
What is byte-proven: GOTAB[257B] = 000000 (level-14 dispatch, a fall-through
with no per-call vector); the FOPEN worker body at 67432B in 006-S3FS is
real code (entry bytes 021127 146145 146131 170006 match the disassembly); and
it drives the open-file lookup - it calls FCON (067002B, link cell 67565),
the file-system connect/context helper.
What is NOT proven: the link from the zero GOTAB slot to the FOPEN worker.
Because the vector is zero there is no stub to disassemble and no pointer to
dereference; dispatch drops into the resident MFELL/CALLPROC second-level
path, which lives in an uncarved overlay. So the MON 257 -> FOPEN
attribution rests on the FOPEN symbol name + its file-lookup behaviour, not a
followed pointer - hence MISATTRIBUTED in the strict sense. Confirming the
link needs a live trace: issue a real MON 257, single-step the level-14
fall-through into the resident CALLPROC dispatch, and confirm P lands on
FOPEN = 67432.
Several link-cell contents (003752, 003776) match no FILSYS-SYMBOLS entry;
their low addresses (below the 26000B segment load base) suggest resident-monitor
/ save-restore routines outside the file-system segment and are not resolved here.
Method: ../../../../../EXTRACTING-RESIDENT-CODE.md - dispatch reality: ../../TASK-05-mismatches.md - master map: ../../MON-CALL-INDEX.md.