Files
psxrecomp/docs/internal/PRINCIPLES.md
Matthew Stanley e6ce5006b4 docs: move root and stale docs into docs/ and docs/internal/
The repository root carried seven markdown files that were not onboarding
material, plus two that had been superseded by the code they described. This
sorts them: reader-facing docs to docs/, working notes to docs/internal/, and
the two superseded ones merged into the docs that replaced them.

Moved to docs/:            WIDESCREEN.md, ENHANCEMENTS.md, TCP_COMMANDS.md
Moved to docs/internal/:   PRINCIPLES.md, ISSUES.md, DEBUG.md, GTE_LM_FIX.md,
                           and from docs/: bios-hardening.md, overlay-status.md,
                           overlay-plan.md, overlay-recompilation-design.md,
                           overlay-discovery.md, TOMBA2_EXC_CONSULT_RESPONSE.md,
                           CASE_A_AOT_GAP.md, audit_inventory.md
Moved to docs/internal/upstream/: UPSTREAM_2026-08-20.md

The root keeps only what belongs there: README.md, CONTRIBUTING.md, LICENSE,
CLAUDE.md, THIRD_PARTY_ATTRIBUTION.md, RELEASE_NOTES.md, the dotfiles and
psxrecomp_cli.py.

MERGES

SPLITGEN_MIGRATION.md folded into docs/BUILDING.md as "Split generated C". Its
migration instructions were stale in a way that mattered: it told every game
repo to hand-edit its CMakeLists and add a file(GLOB ...) over
<serial>_full*.c, but runtime/runtime.cmake now does that itself. GEN_FULL_GLOB
is a multi-value argument of psxrecomp_add_game_runtime(); the loop at
runtime.cmake:1985 makes each pattern absolute against CMAKE_CURRENT_SOURCE_DIR,
expands it with file(GLOB), and concatenates the hits into
GAME_GENERATED_FULL_C. So a title names the pattern and gets however many shards
a regeneration produced. The rewritten section describes that, the two-step
fallback when the globs match nothing (GEN_FULL_FALLBACK, else <serial>_full.c
derived from the dispatch marker by substituting _dispatch.c), and the one
caveat the code actually has: that file(GLOB) is plain, not CONFIGURE_DEPENDS,
so a regeneration which changes the shard COUNT needs a re-configure to be seen.

psxrecomp-toml-readme.md folded into docs/GAME_PROJECT_SETUP.md as "EXE-only
autofill (psxrecomp-toml)", placed after "Disc autofill (probe_disc.py)" and
before "Project Studio" so the two autofill paths sit together. Its documented
flags were checked against the usage text in recompiler/src/main_toml.cpp:28-42
and against the argument parser at :150-165 -- all seven options match with no
drift, so the flag list is reproduced as-is. Added a pointer that probe_disc.py
is preferable when a cue exists, since that tool does the same EXE-header work
plus disc identity and netplay gates.

FUNCTIONAL FIXES

tools/gen_tcp_commands.py wrote to REPO/"TCP_COMMANDS.md". After the move that
path does not exist, so the generator would have created a new stray root file
and --check would have failed against it forever. Retargeted to
REPO/"docs"/"TCP_COMMANDS.md", along with the seven docstring and message
strings that name the path.

Running it surfaced two further problems, both fixed here:

  * The doc was genuinely stale -- pre-existing drift, not introduced by this
    commit (the moved file is byte-identical to origin/master, and no
    debug-server command table is touched here). Four commands registered since
    the last regeneration were missing from the index -- cdrom_timing_dump,
    savestate_status, ws_ui_groups, xprobe_watch -- and scanline had gained a
    backend. Regenerated: 307 -> 311 commands, and the change is confined to the
    AUTOGEN block (the hand-written head and tail are byte-identical to master).
    tools/gen_tcp_commands.py --check now exits 0.
  * DOC.write_text() has no newline argument, so Python translated every newline
    to os.linesep. On Windows that rewrote all 585 lines of the file to CRLF and
    turned a four-line index update into a whole-file diff -- measured: 589 CRLF
    / 0 LF after a run, against 0 CRLF / 585 LF in the repo. Now written through
    an explicit newline="" handle, verified to leave the file at 0 CRLF.

runtime/include/debug_server.h:9 and runtime/src/debug_server.c:8 cited "TCP.md
and DEBUG.md". TCP.md has never existed in this repo under that name; both now
name docs/TCP_COMMANDS.md and docs/internal/DEBUG.md.

LINK AND REFERENCE FIXES

Every inbound reference to a moved file was located by grepping each basename
across the whole tracked tree, not just the markdown. Markdown hrefs in
README.md, CONTRIBUTING.md, docs/ARCHITECTURE.md, docs/COMPILING_OVERLAYS.md,
docs/AOT_OVERLAY_PLAN.md, docs/RELOCATION_MANIFEST_FORMAT.md,
docs/config_schema.md, docs/OVERLAY_XREF.md, docs/TCP_COMMANDS.md and several
docs/internal/ files now point at the new locations; where two files became
siblings under docs/internal/ the path was shortened rather than lengthened
(bios-hardening.md's reference to overlay-discovery.md, for instance).
docs/COMPILING_OVERLAYS.md's "in this folder" phrasing was wrong once two of the
three files it listed moved, so it now names internal/ explicitly.

24 source-comment mentions of ENHANCEMENTS.md sections G1.x across 19 files
(recompiler, runtime, cmake) were retargeted to docs/ENHANCEMENTS.md with the
section numbers untouched. docs/SHADOW_ENHANCEMENTS.md is a DIFFERENT file and
was deliberately excluded.

20 rationale strings citing docs/CASE_A_AOT_GAP.md across the four
recompiler/seeds/*.json files were updated. Done as a byte-level substring
replacement rather than a JSON round-trip: two of those files are stored with
CRLF endings and two with LF, and re-serializing them reformatted 5,700 lines.
The byte-level version changes exactly 20 lines and each file still parses.

References that look similar but point elsewhere were deliberately left alone,
and are worth naming so a future pass does not "fix" them:

  * "recomp-template PRINCIPLES.md" / "NES recomp template PRINCIPLES.md" in
    CLAUDE.md:43, docs/SHADOW_ENHANCEMENTS.md:28,
    docs/internal/HLE_SCHEDULER_CARVEOUT_PLAN.md:5,
    runtime/src/debug_server.c:4934 and tools/parity_diff.py:8 are a different
    repository's file. Only the five that mean this repo's PRINCIPLES.md were
    updated.
  * Every remaining bare ISSUES.md mention is a GAME repo's tracker
    (MegaManX6Recomp 2/7/8/9, TombaRecomp 6), not this repo's.
  * docs/disc-speed.md:4,54,56 and docs/internal/bios-hardening.md:5 name
    overlay-discovery as a BRANCH, not a file, so no path applies.

INDEXES

README.md's "New here?" table gains rows for docs/WIDESCREEN.md,
docs/ENHANCEMENTS.md and docs/TCP_COMMANDS.md. docs/internal/README.md gains
sections indexing all fourteen documents that moved in, plus an "Upstream
contributor reviews" section describing upstream/ and the new sweep file, plus a
"Removed" bullet for CYCLE_TIMING_ARCH.md (deleted in the previous commit)
pointing at FAITHFUL_TIMING_PLAN.md, CYCLE_MODEL_BEETLE.md and
PRECISE_IRQ_SLICE.md -- following the SLJIT_PERSIST_CACHE.md precedent already
in that file.

docs/ENHANCEMENTS.md:7 claimed framework bugs live in "game repos' ISSUES.md
until a framework tracker exists". A framework tracker does exist; it now says
so and names the Beads epic.

VERIFICATION

A link checker was written to scan every tracked *.md for relative links,
resolving each against the tree being scanned. Baseline at origin/master: 129
files, 137 relative links, 3 broken. After both commits: 127 files, 159 relative
links, 3 broken -- the SAME three, all pre-existing and untouched here:

    docs/DATA_SHARDS.md -> INSTANT_LOADS_PARKED.md   (never existed)
    docs/DATA_SHARDS.md -> INSTANT_LOADS_SPIKE2.md   (never existed)
    docs/NETPLAY.md     -> ../lib/recomp-net/README.md  (inside a submodule)

Zero new broken links. The checker's own coverage was checked against a raw grep
for markdown link openers: the 3-link difference is C++ lambdas inside code
blocks, correctly not treated as links.

Also verified: py_compile over all 113 tracked tools/*.py plus psxrecomp_cli.py;
all four seed JSONs still parse; the test-registration guard still reports 123
test files all registered; recompiler/tests/test_coverage_vault.py still passes;
and no file in this commit had its line endings flipped (checked mechanically
across all 50 modified files, after two files were caught and redone).

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
2026-09-03 07:39:07 -07:00

3.1 KiB

PRINCIPLES.md

Global Debugging & Reverse Engineering Principles

This document is the SINGLE source of truth for all rules. All other files reference this. Nothing overrides this.


1. CORE PHILOSOPHY

We do not guess. We do not explore blindly. We do not fix symptoms.

We identify:

  1. The exact point of divergence
  2. The exact state difference
  3. The exact instruction or function responsible

Then we fix that — and only that.


2. STATE OVER THEORY

If two systems behave differently, then their state differs.

All debugging reduces to:

  • Capturing state
  • Comparing state
  • Finding the first difference

Do not theorize causes without state evidence.


3. FIRST DIVERGENCE (CRITICAL)

Never debug the final symptom.

Always find:

The FIRST moment where expected != actual

If you are not identifying the first divergence, you are doing it wrong.


4. TEMPORAL DEBUGGING

Bugs are about WHEN, not WHAT.

Reason in time:

  • What happened before this?
  • What changed?

5. WRITE VS READ BUGS

Determine the class:

Write-time:

  • Wrong data written

Read-time:

  • Correct data, wrong usage

Do not mix these.


6. TRACE THE WRITER

When state differs, find:

  • WHO wrote it
  • WHEN it was written
  • WHY it differs

7. FIX THE SOURCE

Invalid:

  • Clamping
  • Skipping logic
  • Hardcoding values

Valid:

  • Fixing the producing logic
  • Fixing execution order
  • Reproducing missing state

8. MINIMAL FIXES

The correct fix:

  • Smallest possible change
  • Matches original system behavior

9. STRUCTURED DATA ONLY

Use:

  • Ring buffers
  • State snapshots
  • Structured JSON artifacts

Avoid:

  • printf spam
  • unstructured logs
  • log files of any kind

10. BUILD TOOLS, NOT GUESSWORK

If you cannot answer something: -> build a tool to answer it


11. NEVER DEBUG BLIND

If you say:

  • "maybe"
  • "likely"

You are missing data.

Stop and gather it.


12. STUBS (ABSOLUTE RULE)

NO STUBS — EVER

If execution reaches unknown code:

  1. STOP
  2. Identify target
  3. Fix discovery/codegen

Never simulate behavior.


13. FUNCTION DISCOVERY

A dispatch miss is a graph failure.

Fix:

  • function finder
  • codegen

Never patch output.


14. SUCCESS DEFINITION

A bug is fixed only when:

  1. Root cause identified
  2. Divergence explained
  3. Fix addresses cause
  4. Behavior matches reference

15. DISTRUST TOOLING

At the start of every session, validate that tools are doing what you think they're doing. Run a known-good query, check the output by hand, verify file paths resolve where you expect.

Never trust:

  • That a previous session's tool still works the same way
  • That generated output matches what you asked for
  • That a grep/awk pipeline found all matches

When you build a new tool or instrument, verify its FIRST output manually before relying on it for analysis.


16. ORACLES

Truth comes from two sources:

  • Ghidra for what the code is supposed to do (static analysis)
  • DuckStation for what real PS1 hardware does at runtime (dynamic oracle)

Use both, never just one. Don't guess. Don't say "probably". If you cannot answer a question from Ghidra or DuckStation, the answer is "I don't know yet" — not a confident guess.