[riscv64][builtins] Clear c_entry_fp when entering JS and at exception path

Port: 07b03b83

Bug: v8:10026
Change-Id: I4d7dc0fef98aa1754d3aea1d0f5d13b9bad9d645
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3118615
Auto-Submit: Yahan Lu <yahan@iscas.ac.cn>
Commit-Queue: Ji Qiu <qiuji@iscas.ac.cn>
Reviewed-by: Ji Qiu <qiuji@iscas.ac.cn>
Cr-Commit-Position: refs/heads/main@{#76498}

src/builtins/riscv64/builtins-riscv64.cc

@@ -573,9 +573,14 @@ void Generate_JSEntryVariant(MacroAssembler* masm, StackFrame::Type type,
   __ li(s3, Operand(StackFrame::TypeToMarker(type)));
   ExternalReference c_entry_fp = ExternalReference::Create(
       IsolateAddressId::kCEntryFPAddress, masm->isolate());
-  __ li(s4, c_entry_fp);
-  __ Ld(s4, MemOperand(s4));
+  __ li(s5, c_entry_fp);
+  __ Ld(s4, MemOperand(s5));
   __ Push(s1, s2, s3, s4);
+  // Clear c_entry_fp, now we've pushed its previous value to the stack.
+  // If the c_entry_fp is not already zero and we don't clear it, the
+  // SafeStackFrameIterator will assume we are executing C++ and miss the JS
+  // frames on top.
+  __ Sd(zero_reg, MemOperand(s5));
   // Set up frame pointer for the frame to be pushed.
   __ Add64(fp, sp, -EntryFrameConstants::kCallerFPOffset);
   // Registers: