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

libs/libcmt/_flsbuf.obj exact-match ledger

Plain-English scope

This object flushes a byte stream's pending output, writes the next byte, and updates the stream's buffer and error state. It also preserves a subtle CRT rule: when an append-mode stream has no pending buffered bytes, the file position is moved to the end before the new character is placed in the buffer.

The lane is atomic. _flsbuf.obj owns one function, _flsbuf, and no linked data. Matching credit is valid only if that whole function and every symbolic relocation destination are exact.

Authoritative provenance

• Campaign base: fc8e1b076965ed489f291ee233eaad3e1ffaf419.
• Compiler: XDK 3911 Microsoft CL 13.00.9254.1, unchanged libcmt flags /O1 /Gy.
• XDK libcmt.lib SHA-256: 60aa4c87c97eeb6662b31d9d37cf3caba1afabaec72c47b090e7a0ce8b632f55.
• Member: obj/i386/_flsbuf.obj; CodeView source path d:/xbox-finalfre/private/sdktools/crt/crtw32/stdio/_flsbuf.c.
• Microsoft source mirror: xerohour/xbox_leak_may_2020, commit fd00b4b3b2abb1ea6ef9ac64b755419741a3af00, path xbox_leak_may_2020/xbox trunk/xbox/private/sdktools/crt/crtw32/stdio/_flsbuf.c.

The authentic archive and January have the same 281 normalized code bytes and the same nine relocation sites and types. Eight destinations have the same name. At +0xD1, the archive spells the callee _lseek (COFF __lseek), while csplit assigns January's same-address public alias lseek (COFF _lseek). The reconstruction uses the target spelling so the strict comparator remains fail-closed; no symbolic-equivalence waiver is used.

Experiment matrix

ID	Source shape	Result	Disposition
P0	Authentic Microsoft control flow; public FILE; proven 0x28-byte io_info; named private flags; target lseek alias	EXACT: 281/281 bytes, 9/9 strict relocation identities, normalized SHA-256 41ab674b09c6402b46fa49b242b4edb6fc8c8afc6dc216be3b2fcb8a0afeddff	Accepted on the first production build

Original-bug audit

No original defect has been identified. The read-to-write transition at EOF, append seek, buffering fallback, and short-write error are intentional CRT semantics and are preserved.

House/Berth audit

• Readable typed C; no raw offsets, assembly, volatile, forced inline, undefined behavior, byte patches, pragmas, or flag changes.
• Private constants are named and the io_info layout is size-checked.
• The implementation follows Microsoft source topology, with January bytes and relocation identities authoritative where the archive alias spelling differs.
• Parameters are vertically formatted and original behavior is preserved.

Final gates

• Forced _flsbuf.obj rebuild: passed under unchanged /O1 /Gy.
• Hardened function comparison: exact, 281/281 bytes, 9/9 relocation identities, normalized SHA-256 41ab674b09c6402b46fa49b242b4edb6fc8c8afc6dc216be3b2fcb8a0afeddff.
• Relocations are exact at +0x55 -> __iob+32, +0x5D -> __iob+64, +0x65 -> __isatty, +0x70 -> __getbuf, +0x99 -> __write, +0xAF -> ___pioinfo, +0xC1 -> ___badioinfo, +0xD1 -> _lseek, and +0xEC -> __write.
• Whole-object ownership: one external function COMDAT and no linked .data, .rdata, or .bss payload in target or candidate.
• Full halobetacache_build and libcmt_build: passed.
• Progress: 364/833 objects overall; libcmt 97/212 objects, 155/476 functions, and 11,602/55,015 code bytes. This object contributes one object, one function, and 281 code bytes.
• Semantic audit: 465 units and 3,592 functions evaluated, 3,508 accepted exact, and zero unit errors. _flsbuf is accepted by both objdiff and the hardened COFF proof.
• Admission audit: zero candidates, zero revocations, and only the unrelated pre-existing source/shell/shell_xbox contradiction.
• Tool suite: 179/179 tests passed.
• Config JSON, prohibited-construct scan, git diff --check, CRLF source formatting, and final post-commit cleanliness passed.
• The clean-commit per-unit regression snapshot/check is recorded after the atomic commit; it must report _flsbuf as still_exact before handoff.