Cesarus85--mjolnir-vr/docs/object_matching_logs/libcmt_filbuf_obj.md

libs/libcmt/_filbuf.obj exact-match ledger

Plain-English scope

This object refills a buffered byte stream. It rejects closed, string, and write-only streams; obtains or resets a buffer; reads bytes; records EOF/error state; preserves the CRT's text-mode control-Z state; restores the normal buffer size after a small-buffer seek; and returns the first unsigned byte.

The lane is atomic: _filbuf.obj owns one function, _filbuf, and no data section. No matching credit is valid unless that entire function and every relocation destination are exact.

Authoritative provenance

• Campaign base: 96b66de92a33a2aa9bd561f5a292bcc945afdef5.
• Compiler: XDK 3911 Microsoft CL 13.00.9254.1, unchanged libcmt flags /O1 /Gy.
• Archive: XDK 3911 libcmt.lib, SHA-256 60aa4c87c97eeb6662b31d9d37cf3caba1afabaec72c47b090e7a0ce8b632f55.
• Member: obj/i386/_filbuf.obj, extracted SHA-256 472db9c094fc2e691aedf9e9472d24318f2700943d5ee44a9e6d4983458783ff.
• CodeView source path: d:/xbox-finalfre/private/sdktools/crt/crtw32/stdio/_filbuf.c.
• Microsoft source mirror blob: repository xerohour/xbox_leak_may_2020, commit fd00b4b3b2abb1ea6ef9ac64b755419741a3af00, blob 818a017d6aeb35dd01e9e2a96435fb3846177c4a.

The archive and January function have the same 225 bytes after relocation normalization and the same four relocation sites. Three relocation symbols are spelled identically. The fourth is an independently proven symbol alias: the archive calls _read (COFF __read), while csplit assigned January's relocation to read (COFF _read). config/symbols.json places both names at the same executable file offset, 1907598. The reconstructed source uses the target spelling so the hardened comparator can remain fail-closed.

Recovered types and constants

FILE comes from the XDK public header. The private io_info layout is the same proven 0x28-byte runtime layout used by the exact isatty.obj source: the OS handle is at +0, flags at +4, and the remaining fields preserve the authentic CRT stride. Named constants replace the private CRT magic numbers: buffer ownership flags, text/EOF flags, control-Z state, and the 512/4096-byte buffer sizes.

Experiment table

ID	Readable source shape	Result	Disposition
P0	Authentic Microsoft _filbuf.c topology, using target's proven read alias and the exact private io_info layout; spell _osfile_safe as an explicit if/else	225 bytes and 4 relocations, but the __badioinfo and __pioinfo paths were emitted in the opposite order at +0x6d	Rejected; readable but does not preserve the macro's conditional-expression topology
P1	Replace only that if/else with file == -1 ? bad : normal	225/4, but VC7 still emitted the bad-info arm first; normalized hash 18fd825f...	Rejected; conditional arm order is IR-significant
P2	Spell the equivalent authentic macro topology as file != -1 ? normal : bad	EXACT: 225 bytes, 4/4 relocation identities, normalized SHA-256 48b372b08e6ad34df25c4016b69c5b4a13c88647ebaf2afeef3cf9041f7edc2b	Accepted; this recovers the authentic macro arm order without retaining an unavailable private header

No compiler flag, pragma, assembly, volatile, forced inline, undefined behavior, byte patch, or comparator exception is permitted in this lane.

Original-bug audit

No original defect was found. The apparently unusual stream->_cnt ? _IOERR : _IOEOF expression is intentional: read == 0 means EOF and read == -1 means error. The 0xff mask intentionally returns an unsigned input byte.

House/Berth audit checklist

• Readable typed C; no raw byte-offset access.
• Parameters are vertically formatted.
• Named constants replace unexplained private CRT values.
• The function's return type and all external declarations are explicit.
• Original behavior is preserved rather than silently repaired.
• Exactness requires byte, size, relocation address/type/destination, symbol ownership, full-build, regression, semantic/admission, and test evidence.

Final gate record

• Forced _filbuf.obj rebuild: passed with unchanged /O1 /Gy flags.
• Hardened function comparison: exact, 225/225 bytes, 4/4 relocations, hash 48b372b08e6ad34df25c4016b69c5b4a13c88647ebaf2afeef3cf9041f7edc2b.
• Relocations: _getbuf@+0x35, read@+0x4b, __pioinfo@+0x77, and __badioinfo@+0x87; every address, type, target, and addend is exact.
• Whole-object ownership: one external function COMDAT and no .data, .rdata, or .bss payload in target or candidate.
• Full halobetacache_build: passed.
• Full libcmt_build: passed.
• Semantic audit: 453 units scanned, 3,566 functions evaluated, zero unit errors; _filbuf accepted by both objdiff and the semantic COFF proof.
• Admission audit: zero candidates, one unrelated pre-existing shell_xbox contradiction, and zero revoked units.
• Progress after the final rebase: libcmt 84/212 objects and 129/476 functions; _filbuf.obj contributes one object, one function, and 225 code bytes.
• Tool tests: 179/179 passed.
• Prohibited-construct scan and git diff --check: passed.
• Rebased onto authoritative campaign tip 2cb1bb27; the forced comparison, both full builds, semantic/admission audits, 179 tests, and a clean regression snapshot/check were all repeated successfully after the rebase.