Use footer address which is loaded into frame pointer to find generator frames

Summary: On ARM the callee is preserving the frame register - so when a JITed function calls out with it's frame register pointing at the footer data that's the value that we will see in our callees saved register. So to identify the IP of the JIT generator function we look for the footer rather than the original frame.

Reviewed By: kddnewton

Differential Revision: D93525511

fbshipit-source-id: 0612a4144396fa455017a0e33296b37ba8705a50

Author: DinoV

cinderx/Jit/frame.cpp

@@ -100,7 +100,17 @@ uintptr_t getIP(_PyInterpreterFrame* frame, int frame_size) {
     auto footer = jitGenDataFooter(gen);
     if (footer->yieldPoint == nullptr) {
       // The generator is running.
+#if defined(__x86_64__)
+      // On x86, we read the return address from a fixed offset on the real
+      // stack relative to the resume function's RBP.
       frame_base = footer->originalFramePointer;
+#elif defined(__aarch64__)
+      // On ARM64, we walk the frame pointer chain to find the JIT frame.
+      // During generator execution, FP is set to the GenDataFooter pointer
+      // (gi_jit_data), so that's what callees save as their frame pointer
+      // and what we need to match against in the chain.
+      frame_base = reinterpret_cast<uintptr_t>(footer);
+#endif
     } else {
       // The generator is suspended.
       return footer->yieldPoint->resumeTarget();