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Development notes

Open problems, the bug list (so you recognise symptoms), and a short history.

Remaining hot spots / next steps (rough priority)

  1. JIT code quality (still the biggest lever): the first round (fusion, dead flag stores, a write-through register cache inside a block) is done, see "JIT code quality work". Remaining: registers still reload at every block boundary (a loop iteration is one block), the TBI mask (shl/shr 8) on every access, block-exit/IBTC cost, flags kept as four bytes.
  2. Still-interpreted instructions: SHA-256 (sha256h/h2/su0/su1), sys (dc zva/cvau…), tbl, FRINT*, FCVTZU, UCVTF vector, unsigned/other shifts (SQSHL…), FMAX/FMIN, FMADD (needs FMA or double-double), LDXR/STXR exclusives, many rarer NEON ops. Use MACLATOR_FALLBACK_HIST on the GPU (--type=gpu-process) and renderer processes to see what matters.
  3. Startup: work is ~10 processes on 4 cores; per-process translation. Ideas: pre-warm AOT, fewer VS Code processes/features, check Chromium/Electron flags (--in-process-gpu, --disable-features=…), persistent V8 code cache (don't wipe the profile dir).
  4. Chromium-specific: run with a real profile; check about:blank page target had url "" for a long time in one run (renderer for the initial page slow to start) — investigate.
  5. GPU: done for Chromium via the Metal bridge (see "GPU passthrough"); apps that present through CAMetalLayer/MTKView directly still need that bridged.
  6. Robustness: stale-IBTC hazard if a thread only ever hits IBTC entries after invalidation (accepted risk); AOT profile saving only on graceful exit; concurrent builders write the same files (last writer wins, atomic rename); MACLATOR_SPIN_DEBUG for infinite-dispatch bugs.
  7. Overcast / iOS-on-Mac apps: would need the iOS-on-Mac runtime and unencrypted binaries; FairPlay-encrypted App Store binaries are not runnable off Apple Silicon and circumventing DRM is out of scope. Suggested alternative: build your own UIKit "Designed for iPad" or Mac Catalyst app.

Key bugs found & fixed (so you recognise symptoms)

  • --sysroot was parsed but never used; dyld walks paths via dirfd (fixed with vpath tracking).
  • Host rejects arm64 code signatures (errno 85) → emulate fcntl code-sign ops.
  • libobjc aborts on task_restartable_ranges_register → patch mach_msg2 reply.
  • Non-canonical address GP faults from TBI-tagged pointers → mask in interp and JIT.
  • IOKit: MobileGestalt waits forever for AppleDiagnosticDataAccessReadOnly → fake service+iterator.
  • libdispatch timers never fire → event-manager QoS lost on fired events.
  • Two event-manager threads → libdispatch "Locking the manager should not fail".
  • bsdthread_ctl EINVAL → libdispatch "_pthread_set_properties_self failed".
  • 4K vs 16K pages → V8 allocator crash (munmap EINVAL) → 16K mmap.
  • posix_spawn of arm64 helpers failed on the Intel kernel → re-launch through maclator.
  • JIT cache exhausted / thrash from flush-all invalidation → per-unit invalidation, 4 GiB cache.
  • Forked child spun forever (stale task port) → libc fork.
  • Vacuous self-tests (fallback == interpreter) → report native= count.
  • Wrong bit masks pinned the U bit for unsigned SIMD variants (umull/raddhn/ushr/ushll/uminv).
  • AdvSIMD load/store were never routed to the SIMD translator (dispatched via ldst).
  • LD4/ST4 element size is bits 11:10 (not 23:22).
  • Two labels at the same address need a nop between (iced).
  • Exec-mmap of AOT files triggers Gatekeeper dialogs → copy into the code cache.
  • Chromium hang: profiler thread_suspend (msg id 3605) → no-op shim.

Session log summary (chronological)

  1. Obtained arm64e dyld cache (macOS 26.6.2) on the test Mac via ipsw partial IPSW extraction (26.7/25G229 not indexed). 2. Made fastfetch, then neatvi, run on the test Mac. 3. IOKit shim, FP16 NEON, dispatch timers, single event manager → AppKit calculator. 4. 16K pages, arm64 child spawn, libc fork, precise invalidation → VS Code Electron boots. 5. Long performance campaign (native NEON/atomics, AOT for libs, invalidation) using VS Code as the benchmark.
  2. maclator ./binary auto-sysroot. 7. Chromium snapshot downloaded to Downloads (both Macs), thread-suspend shim, Gatekeeper fix → Chromium renders.