[edusperoni]

What

• build-ios.sh: Catalyst variants now pass v8_enable_lite_mode=false, so they ship Sparkplug, Maglev and TurboFan.
• New patches/v8_catalyst_jit_write_protect.patch, applied by fetch.sh for iOS fetches, so V8's JIT works inside a Catalyst process.
• tests/apple-args.py asserts the Catalyst arg; the README documents the patch and the arg.

Why

Catalyst has been lite mode all along. The comment in build-ios.sh says Catalyst is "deliberately not lite", but gni/v8.gni turns v8_enable_lite_mode on for every target_platform="iphoneos" build, and Catalyst is only a target_environment of that platform. The shipped -7 Catalyst libv8_compiler.a is ~1.5 KB, --trace-opt reports nothing, and hot JS runs at --jitless speed.

A JIT build alone crashes on Apple silicon. Catalyst compiles as iOS (TARGET_OS_IPHONE), so V8 picks its iOS JIT-memory model, which assumes MAP_JIT pages are writable and executable at once. A Catalyst process runs on macOS, where MAP_JIT pages are per-thread W^X, so the first JIT code write raises SIGBUS, even with com.apple.security.cs.allow-jit. The patch gives Catalyst the macOS model:

• V8_HAS_PTHREAD_JIT_WRITE_PROTECT for Catalyst arm64, so RwxMemoryWriteScope toggles pthread_jit_write_protect_np. The SDK marks that function unavailable on Catalyst, so it's resolved once with dlsym; libpthread on macOS exports it.
• The macOS code-range pre-commit and the recommit when re-embedding builtins, which the iOS branches skip.

Everything is gated on a new internal V8_OS_MACCATALYST (set in src/base/build_config.h, not in a public header), so device, simulator, tvOS and Android builds compile the same code as before.

Verification

Local arm64 Catalyst build of 14.9.207.39 with the existing patches plus this one, linked into a small macabi probe that runs a hot loop and a regex:

Signing	--jitless	JIT	--trace-opt
ad-hoc	385 ms	11 ms	7 optimized
hardened + allow-jit	379 ms	11 ms	7 optimized
hardened + allow-unsigned-executable-memory	383 ms	13 ms	7 optimized
hardened, no entitlement	391 ms	SIGTRAP at startup	—

Without either entitlement the process can't map JIT memory, and V8 doesn't fall back on its own, so the iOS runtime passes --jitless in that case (companion runtime PR). Without the patch, all three JIT rows SIGBUS.

python3 tests/apple-args.py passes. x64-catalyst picks up the same arg; Intel Macs have no per-thread W^X, so the patch is a no-op there. I couldn't run that slice locally.

Size

Stripped arm64 Catalyst NativeScript.framework: 13.27 MB → 22.89 MB (+9.6 MB), about +2.7 MB zipped. This affects the Catalyst slice only.

Release

The runtime consumes this through a tagged release (v8-*), so it needs a tag after merge, e.g. v8-14.9.207.39-8.

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