Add m-esr52 at 52.6.0

1 files changed, 1229 insertions, 0 deletions

diff --git a/js/src/jit/arm64/Trampoline-arm64.cpp b/js/src/jit/arm64/Trampoline-arm64.cpp
new file mode 100644
index 000000000..547bdd927
--- /dev/null
+++ b/js/src/jit/arm64/Trampoline-arm64.cpp
@@ -0,0 +1,1229 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "jit/Bailouts.h"
+#include "jit/JitCompartment.h"
+#include "jit/JitFrames.h"
+#include "jit/Linker.h"
+#ifdef JS_ION_PERF
+# include "jit/PerfSpewer.h"
+#endif
+#include "jit/arm64/SharedICHelpers-arm64.h"
+#include "jit/VMFunctions.h"
+
+#include "jit/MacroAssembler-inl.h"
+
+using namespace js;
+using namespace js::jit;
+
+// All registers to save and restore. This includes the stack pointer, since we
+// use the ability to reference register values on the stack by index.
+static const LiveRegisterSet AllRegs =
+    LiveRegisterSet(GeneralRegisterSet(Registers::AllMask & ~(1 << 31 | 1 << 30 | 1 << 29| 1 << 28)),
+                FloatRegisterSet(FloatRegisters::AllMask));
+
+/* This method generates a trampoline on ARM64 for a c++ function with
+ * the following signature:
+ *   bool blah(void* code, int argc, Value* argv, JSObject* scopeChain, Value* vp)
+ *   ...using standard AArch64 calling convention
+ */
+JitCode*
+JitRuntime::generateEnterJIT(JSContext* cx, EnterJitType type)
+{
+    MacroAssembler masm(cx);
+
+    const Register reg_code      = IntArgReg0; // EnterJitData::jitcode.
+    const Register reg_argc      = IntArgReg1; // EnterJitData::maxArgc.
+    const Register reg_argv      = IntArgReg2; // EnterJitData::maxArgv.
+    const Register reg_osrFrame  = IntArgReg3; // EnterJitData::osrFrame.
+    const Register reg_callee    = IntArgReg4; // EnterJitData::calleeToken.
+    const Register reg_scope     = IntArgReg5; // EnterJitData::scopeChain.
+    const Register reg_osrNStack = IntArgReg6; // EnterJitData::osrNumStackValues.
+    const Register reg_vp        = IntArgReg7; // Address of EnterJitData::result.
+
+    MOZ_ASSERT(OsrFrameReg == IntArgReg3);
+
+    // During the pushes below, use the normal stack pointer.
+    masm.SetStackPointer64(sp);
+
+    // Save old frame pointer and return address; set new frame pointer.
+    masm.push(r29, r30);
+    masm.moveStackPtrTo(r29);
+
+    // Save callee-save integer registers.
+    // Also save x7 (reg_vp) and x30 (lr), for use later.
+    masm.push(r19, r20, r21, r22);
+    masm.push(r23, r24, r25, r26);
+    masm.push(r27, r28, r7,  r30);
+
+    // Save callee-save floating-point registers.
+    // AArch64 ABI specifies that only the lower 64 bits must be saved.
+    masm.push(d8,  d9,  d10, d11);
+    masm.push(d12, d13, d14, d15);
+
+#ifdef DEBUG
+    // Emit stack canaries.
+    masm.movePtr(ImmWord(0xdeadd00d), r23);
+    masm.movePtr(ImmWord(0xdeadd11d), r24);
+    masm.push(r23, r24);
+#endif
+
+    // Common code below attempts to push single registers at a time,
+    // which breaks the stack pointer's 16-byte alignment requirement.
+    // Note that movePtr() is invalid because StackPointer is treated as xzr.
+    //
+    // FIXME: After testing, this entire function should be rewritten to not
+    // use the PseudoStackPointer: since the amount of data pushed is precalculated,
+    // we can just allocate the whole frame header at once and index off sp.
+    // This will save a significant number of instructions where Push() updates sp.
+    masm.Mov(PseudoStackPointer64, sp);
+    masm.SetStackPointer64(PseudoStackPointer64);
+
+    // Save the stack pointer at this point for Baseline OSR.
+    masm.moveStackPtrTo(BaselineFrameReg);
+    // Remember stack depth without padding and arguments.
+    masm.moveStackPtrTo(r19);
+
+    // If constructing, include newTarget in argument vector.
+    {
+        Label noNewTarget;
+        Imm32 constructingToken(CalleeToken_FunctionConstructing);
+        masm.branchTest32(Assembler::Zero, reg_callee, constructingToken, &noNewTarget);
+        masm.add32(Imm32(1), reg_argc);
+        masm.bind(&noNewTarget);
+    }
+
+    // JitFrameLayout is as follows (higher is higher in memory):
+    //  N*8  - [ JS argument vector ] (base 16-byte aligned)
+    //  8    - numActualArgs
+    //  8    - calleeToken (16-byte aligned)
+    //  8    - frameDescriptor
+    //  8    - returnAddress (16-byte aligned, pushed by callee)
+
+    // Push the argument vector onto the stack.
+    // WARNING: destructively modifies reg_argv
+    {
+        vixl::UseScratchRegisterScope temps(&masm.asVIXL());
+
+        const ARMRegister tmp_argc = temps.AcquireX();
+        const ARMRegister tmp_sp = temps.AcquireX();
+
+        Label noArguments;
+        Label loopHead;
+
+        masm.movePtr(reg_argc, tmp_argc.asUnsized());
+
+        // sp -= 8
+        // Since we're using PostIndex Str below, this is necessary to avoid overwriting
+        // the SPS mark pushed above.
+        masm.subFromStackPtr(Imm32(8));
+
+        // sp -= 8 * argc
+        masm.Sub(PseudoStackPointer64, PseudoStackPointer64, Operand(tmp_argc, vixl::SXTX, 3));
+
+        // Give sp 16-byte alignment and sync stack pointers.
+        masm.andToStackPtr(Imm32(~0xff));
+        masm.moveStackPtrTo(tmp_sp.asUnsized());
+
+        masm.branchTestPtr(Assembler::Zero, reg_argc, reg_argc, &noArguments);
+
+        // Begin argument-pushing loop.
+        // This could be optimized using Ldp and Stp.
+        {
+            masm.bind(&loopHead);
+
+            // Load an argument from argv, then increment argv by 8.
+            masm.Ldr(x24, MemOperand(ARMRegister(reg_argv, 64), Operand(8), vixl::PostIndex));
+
+            // Store the argument to tmp_sp, then increment tmp_sp by 8.
+            masm.Str(x24, MemOperand(tmp_sp, Operand(8), vixl::PostIndex));
+
+            // Set the condition codes for |cmp tmp_argc, 2| (using the old value).
+            masm.Subs(tmp_argc, tmp_argc, Operand(1));
+
+            // Branch if arguments remain.
+            masm.B(&loopHead, vixl::Condition::ge);
+        }
+
+        masm.bind(&noArguments);
+    }
+    masm.checkStackAlignment();
+
+    // Push the number of actual arguments and the calleeToken.
+    // The result address is used to store the actual number of arguments
+    // without adding an argument to EnterJIT.
+    masm.unboxInt32(Address(reg_vp, 0x0), ip0);
+    masm.push(ip0, reg_callee);
+    masm.checkStackAlignment();
+
+    // Calculate the number of bytes pushed so far.
+    masm.subStackPtrFrom(r19);
+
+    // Push the frameDescriptor.
+    masm.makeFrameDescriptor(r19, JitFrame_Entry, JitFrameLayout::Size());
+    masm.Push(r19);
+
+    Label osrReturnPoint;
+    if (type == EnterJitBaseline) {
+        // Check for OSR.
+        Label notOsr;
+        masm.branchTestPtr(Assembler::Zero, OsrFrameReg, OsrFrameReg, &notOsr);
+
+        // Push return address and previous frame pointer.
+        masm.Adr(ScratchReg2_64, &osrReturnPoint);
+        masm.push(ScratchReg2, BaselineFrameReg);
+
+        // Reserve frame.
+        masm.subFromStackPtr(Imm32(BaselineFrame::Size()));
+        masm.moveStackPtrTo(BaselineFrameReg);
+
+        // Reserve space for locals and stack values.
+        masm.Lsl(w19, ARMRegister(reg_osrNStack, 32), 3); // w19 = num_stack_values * sizeof(Value).
+        masm.subFromStackPtr(r19);
+
+        // Enter exit frame.
+        masm.addPtr(Imm32(BaselineFrame::Size() + BaselineFrame::FramePointerOffset), r19);
+        masm.makeFrameDescriptor(r19, JitFrame_BaselineJS, ExitFrameLayout::Size());
+        masm.asVIXL().Push(x19, xzr); // Push xzr for a fake return address.
+        // No GC things to mark: push a bare token.
+        masm.enterFakeExitFrame(ExitFrameLayoutBareToken);
+
+        masm.push(BaselineFrameReg, reg_code);
+
+        // Initialize the frame, including filling in the slots.
+        masm.setupUnalignedABICall(r19);
+        masm.passABIArg(BaselineFrameReg); // BaselineFrame.
+        masm.passABIArg(reg_osrFrame); // InterpreterFrame.
+        masm.passABIArg(reg_osrNStack);
+        masm.callWithABI(JS_FUNC_TO_DATA_PTR(void*, jit::InitBaselineFrameForOsr));
+
+        masm.pop(r19, BaselineFrameReg);
+        MOZ_ASSERT(r19 != ReturnReg);
+
+        masm.addToStackPtr(Imm32(ExitFrameLayout::SizeWithFooter()));
+        masm.addPtr(Imm32(BaselineFrame::Size()), BaselineFrameReg);
+
+        Label error;
+        masm.branchIfFalseBool(ReturnReg, &error);
+
+        masm.jump(r19);
+
+        // OOM: load error value, discard return address and previous frame
+        // pointer, and return.
+        masm.bind(&error);
+        masm.Add(masm.GetStackPointer64(), BaselineFrameReg64, Operand(2 * sizeof(uintptr_t)));
+        masm.syncStackPtr();
+        masm.moveValue(MagicValue(JS_ION_ERROR), JSReturnOperand);
+        masm.B(&osrReturnPoint);
+
+        masm.bind(&notOsr);
+        masm.movePtr(reg_scope, R1_);
+    }
+
+    // Call function.
+    // Since AArch64 doesn't have the pc register available, the callee must push lr.
+    masm.callJitNoProfiler(reg_code);
+
+    // Baseline OSR will return here.
+    if (type == EnterJitBaseline)
+        masm.bind(&osrReturnPoint);
+
+    // Return back to SP.
+    masm.Pop(r19);
+    masm.Add(masm.GetStackPointer64(), masm.GetStackPointer64(),
+             Operand(x19, vixl::LSR, FRAMESIZE_SHIFT));
+    masm.syncStackPtr();
+    masm.SetStackPointer64(sp);
+
+#ifdef DEBUG
+    // Check that canaries placed on function entry are still present.
+    masm.pop(r24, r23);
+    Label x23OK, x24OK;
+
+    masm.branchPtr(Assembler::Equal, r23, ImmWord(0xdeadd00d), &x23OK);
+    masm.breakpoint();
+    masm.bind(&x23OK);
+
+    masm.branchPtr(Assembler::Equal, r24, ImmWord(0xdeadd11d), &x24OK);
+    masm.breakpoint();
+    masm.bind(&x24OK);
+#endif
+
+    // Restore callee-save floating-point registers.
+    masm.pop(d15, d14, d13, d12);
+    masm.pop(d11, d10,  d9,  d8);
+
+    // Restore callee-save integer registers.
+    // Also restore x7 (reg_vp) and x30 (lr).
+    masm.pop(r30, r7,  r28, r27);
+    masm.pop(r26, r25, r24, r23);
+    masm.pop(r22, r21, r20, r19);
+
+    // Store return value (in JSReturnReg = x2 to just-popped reg_vp).
+    masm.storeValue(JSReturnOperand, Address(reg_vp, 0));
+
+    // Restore old frame pointer.
+    masm.pop(r30, r29);
+
+    // Return using the value popped into x30.
+    masm.abiret();
+
+    Linker linker(masm);
+    AutoFlushICache afc("EnterJIT");
+    JitCode* code = linker.newCode<NoGC>(cx, OTHER_CODE);
+
+#ifdef JS_ION_PERF
+    writePerfSpewerJitCodeProfile(code, "EnterJIT");
+#endif
+
+    return code;
+}
+
+JitCode*
+JitRuntime::generateInvalidator(JSContext* cx)
+{
+    MacroAssembler masm;
+
+    masm.push(r0, r1, r2, r3);
+
+    masm.PushRegsInMask(AllRegs);
+    masm.moveStackPtrTo(r0);
+
+    masm.Sub(x1, masm.GetStackPointer64(), Operand(sizeof(size_t)));
+    masm.Sub(x2, masm.GetStackPointer64(), Operand(sizeof(size_t) + sizeof(void*)));
+    masm.moveToStackPtr(r2);
+
+    masm.setupUnalignedABICall(r10);
+    masm.passABIArg(r0);
+    masm.passABIArg(r1);
+    masm.passABIArg(r2);
+
+    masm.callWithABI(JS_FUNC_TO_DATA_PTR(void*, InvalidationBailout));
+
+    masm.pop(r2, r1);
+
+    masm.Add(masm.GetStackPointer64(), masm.GetStackPointer64(), x1);
+    masm.Add(masm.GetStackPointer64(), masm.GetStackPointer64(),
+             Operand(sizeof(InvalidationBailoutStack)));
+    masm.syncStackPtr();
+
+    JitCode* bailoutTail = cx->runtime()->jitRuntime()->getBailoutTail();
+    masm.branch(bailoutTail);
+
+    Linker linker(masm);
+    AutoFlushICache afc("Invalidator");
+    return linker.newCode<NoGC>(cx, OTHER_CODE);
+}
+
+JitCode*
+JitRuntime::generateArgumentsRectifier(JSContext* cx, void** returnAddrOut)
+{
+    MacroAssembler masm;
+
+    // Save the return address for later.
+    masm.push(lr);
+
+    // Load the information that the rectifier needs from the stack.
+    masm.Ldr(w0, MemOperand(masm.GetStackPointer64(), RectifierFrameLayout::offsetOfNumActualArgs()));
+    masm.Ldr(x1, MemOperand(masm.GetStackPointer64(), RectifierFrameLayout::offsetOfCalleeToken()));
+
+    // Extract a JSFunction pointer from the callee token and keep the
+    // intermediary to avoid later recalculation.
+    masm.And(x5, x1, Operand(CalleeTokenMask));
+
+    // Get the arguments from the function object.
+    masm.Ldrh(x6, MemOperand(x5, JSFunction::offsetOfNargs()));
+
+    static_assert(CalleeToken_FunctionConstructing == 0x1, "Constructing must be low-order bit");
+    masm.And(x4, x1, Operand(CalleeToken_FunctionConstructing));
+    masm.Add(x7, x6, x4);
+
+    // Calculate the position that our arguments are at before sp gets modified.
+    MOZ_ASSERT(ArgumentsRectifierReg == r8, "x8 used for argc in Arguments Rectifier");
+    masm.Add(x3, masm.GetStackPointer64(), Operand(x8, vixl::LSL, 3));
+    masm.Add(x3, x3, Operand(sizeof(RectifierFrameLayout)));
+
+    // Pad to a multiple of 16 bytes. This neglects the |this| value,
+    // which will also be pushed, because the rest of the frame will
+    // round off that value. See pushes of |argc|, |callee| and |desc| below.
+    Label noPadding;
+    masm.Tbnz(x7, 0, &noPadding);
+    masm.asVIXL().Push(xzr);
+    masm.Add(x7, x7, Operand(1));
+    masm.bind(&noPadding);
+
+    {
+        Label notConstructing;
+        masm.Cbz(x4, &notConstructing);
+
+        // new.target lives at the end of the pushed args
+        // NB: The arg vector holder starts at the beginning of the last arg,
+        //     add a value to get to argv[argc]
+        masm.loadPtr(Address(r3, sizeof(Value)), r4);
+        masm.Push(r4);
+
+        masm.bind(&notConstructing);
+    }
+
+    // Calculate the number of undefineds that need to be pushed.
+    masm.Sub(w2, w6, w8);
+
+    // Put an undefined in a register so it can be pushed.
+    masm.moveValue(UndefinedValue(), r4);
+
+    // Push undefined N times.
+    {
+        Label undefLoopTop;
+        masm.bind(&undefLoopTop);
+        masm.Push(r4);
+        masm.Subs(w2, w2, Operand(1));
+        masm.B(&undefLoopTop, Assembler::NonZero);
+    }
+
+    // Arguments copy loop. Copy for x8 >= 0 to include |this|.
+    {
+        Label copyLoopTop;
+        masm.bind(&copyLoopTop);
+        masm.Ldr(x4, MemOperand(x3, -sizeof(Value), vixl::PostIndex));
+        masm.Push(r4);
+        masm.Subs(x8, x8, Operand(1));
+        masm.B(&copyLoopTop, Assembler::NotSigned);
+    }
+
+    // Fix up the size of the stack frame. +1 accounts for |this|.
+    masm.Add(x6, x7, Operand(1));
+    masm.Lsl(x6, x6, 3);
+
+    // Make that into a frame descriptor.
+    masm.makeFrameDescriptor(r6, JitFrame_Rectifier, JitFrameLayout::Size());
+
+    masm.push(r0,  // Number of actual arguments.
+              r1,  // Callee token.
+              r6); // Frame descriptor.
+
+    // Load the address of the code that is getting called.
+    masm.Ldr(x3, MemOperand(x5, JSFunction::offsetOfNativeOrScript()));
+    masm.loadBaselineOrIonRaw(r3, r3, nullptr);
+    uint32_t returnOffset = masm.callJitNoProfiler(r3);
+
+    // Clean up!
+    // Get the size of the stack frame, and clean up the later fixed frame.
+    masm.Ldr(x4, MemOperand(masm.GetStackPointer64(), 24, vixl::PostIndex));
+
+    // Now that the size of the stack frame sans the fixed frame has been loaded,
+    // add that onto the stack pointer.
+    masm.Add(masm.GetStackPointer64(), masm.GetStackPointer64(),
+             Operand(x4, vixl::LSR, FRAMESIZE_SHIFT));
+
+    // Pop the return address from earlier and branch.
+    masm.ret();
+
+    Linker linker(masm);
+    AutoFlushICache afc("ArgumentsRectifier");
+    JitCode* code = linker.newCode<NoGC>(cx, OTHER_CODE);
+
+    if (returnAddrOut)
+        *returnAddrOut = (void*) (code->raw() + returnOffset);
+
+    return code;
+}
+
+static void
+PushBailoutFrame(MacroAssembler& masm, uint32_t frameClass, Register spArg)
+{
+    // the stack should look like:
+    // [IonFrame]
+    // bailoutFrame.registersnapshot
+    // bailoutFrame.fpsnapshot
+    // bailoutFrame.snapshotOffset
+    // bailoutFrame.frameSize
+
+    // STEP 1a: Save our register sets to the stack so Bailout() can read
+    // everything.
+    // sp % 8 == 0
+
+    // We don't have to push everything, but this is likely easier.
+    // Setting regs_.
+    masm.subFromStackPtr(Imm32(Registers::TotalPhys * sizeof(void*)));
+    for (uint32_t i = 0; i < Registers::TotalPhys; i += 2) {
+        masm.Stp(ARMRegister::XRegFromCode(i),
+                 ARMRegister::XRegFromCode(i + 1),
+                 MemOperand(masm.GetStackPointer64(), i * sizeof(void*)));
+    }
+
+    // Since our datastructures for stack inspection are compile-time fixed,
+    // if there are only 16 double registers, then we need to reserve
+    // space on the stack for the missing 16.
+    masm.subFromStackPtr(Imm32(FloatRegisters::TotalPhys * sizeof(double)));
+    for (uint32_t i = 0; i < FloatRegisters::TotalPhys; i += 2) {
+        masm.Stp(ARMFPRegister::DRegFromCode(i),
+                 ARMFPRegister::DRegFromCode(i + 1),
+                 MemOperand(masm.GetStackPointer64(), i * sizeof(void*)));
+    }
+
+    // STEP 1b: Push both the "return address" of the function call (the address
+    //          of the instruction after the call that we used to get here) as
+    //          well as the callee token onto the stack. The return address is
+    //          currently in r14. We will proceed by loading the callee token
+    //          into a sacrificial register <= r14, then pushing both onto the
+    //          stack.
+
+    // Now place the frameClass onto the stack, via a register.
+    masm.Mov(x9, frameClass);
+
+    // And onto the stack. Since the stack is full, we need to put this one past
+    // the end of the current stack. Sadly, the ABI says that we need to always
+    // point to the lowest place that has been written. The OS is free to do
+    // whatever it wants below sp.
+    masm.push(r30, r9);
+    masm.moveStackPtrTo(spArg);
+}
+
+static void
+GenerateBailoutThunk(JSContext* cx, MacroAssembler& masm, uint32_t frameClass)
+{
+    PushBailoutFrame(masm, frameClass, r0);
+
+    // SP % 8 == 4
+    // STEP 1c: Call the bailout function, giving a pointer to the
+    //          structure we just blitted onto the stack.
+    // Make space for the BaselineBailoutInfo* outparam.
+    const int sizeOfBailoutInfo = sizeof(void*) * 2;
+    masm.reserveStack(sizeOfBailoutInfo);
+    masm.moveStackPtrTo(r1);
+
+    masm.setupUnalignedABICall(r2);
+    masm.passABIArg(r0);
+    masm.passABIArg(r1);
+    masm.callWithABI(JS_FUNC_TO_DATA_PTR(void*, Bailout));
+
+    masm.Ldr(x2, MemOperand(masm.GetStackPointer64(), 0));
+    masm.addToStackPtr(Imm32(sizeOfBailoutInfo));
+
+    static const uint32_t BailoutDataSize = sizeof(void*) * Registers::Total +
+                                            sizeof(double) * FloatRegisters::TotalPhys;
+
+    if (frameClass == NO_FRAME_SIZE_CLASS_ID) {
+        vixl::UseScratchRegisterScope temps(&masm.asVIXL());
+        const ARMRegister scratch64 = temps.AcquireX();
+
+        masm.Ldr(scratch64, MemOperand(masm.GetStackPointer64(), sizeof(uintptr_t)));
+        masm.addToStackPtr(Imm32(BailoutDataSize + 32));
+        masm.addToStackPtr(scratch64.asUnsized());
+    } else {
+        uint32_t frameSize = FrameSizeClass::FromClass(frameClass).frameSize();
+        masm.addToStackPtr(Imm32(frameSize + BailoutDataSize + sizeof(void*)));
+    }
+
+    // Jump to shared bailout tail. The BailoutInfo pointer has to be in r9.
+    JitCode* bailoutTail = cx->runtime()->jitRuntime()->getBailoutTail();
+    masm.branch(bailoutTail);
+}
+
+JitCode*
+JitRuntime::generateBailoutTable(JSContext* cx, uint32_t frameClass)
+{
+    // FIXME: Implement.
+    MacroAssembler masm;
+    masm.breakpoint();
+    Linker linker(masm);
+    AutoFlushICache afc("BailoutTable");
+    return linker.newCode<NoGC>(cx, OTHER_CODE);
+}
+
+JitCode*
+JitRuntime::generateBailoutHandler(JSContext* cx)
+{
+    MacroAssembler masm(cx);
+    GenerateBailoutThunk(cx, masm, NO_FRAME_SIZE_CLASS_ID);
+
+#ifdef JS_ION_PERF
+    writePerfSpewerJitCodeProfile(code, "BailoutHandler");
+#endif
+
+    Linker linker(masm);
+    AutoFlushICache afc("BailoutHandler");
+    return linker.newCode<NoGC>(cx, OTHER_CODE);
+}
+
+JitCode*
+JitRuntime::generateVMWrapper(JSContext* cx, const VMFunction& f)
+{
+    MOZ_ASSERT(functionWrappers_);
+    MOZ_ASSERT(functionWrappers_->initialized());
+    VMWrapperMap::AddPtr p = functionWrappers_->lookupForAdd(&f);
+    if (p)
+        return p->value();
+
+    MacroAssembler masm(cx);
+
+    // Avoid conflicts with argument registers while discarding the result after
+    // the function call.
+    AllocatableGeneralRegisterSet regs(Register::Codes::WrapperMask);
+
+    // Wrapper register set is a superset of the Volatile register set.
+    JS_STATIC_ASSERT((Register::Codes::VolatileMask & ~Register::Codes::WrapperMask) == 0);
+
+    // Unlike on other platforms, it is the responsibility of the VM *callee* to
+    // push the return address, while the caller must ensure that the address
+    // is stored in lr on entry. This allows the VM wrapper to work with both direct
+    // calls and tail calls.
+    masm.push(lr);
+
+    // First argument is the JSContext.
+    Register reg_cx = IntArgReg0;
+    regs.take(reg_cx);
+
+    // Stack is:
+    //    ... frame ...
+    //  +12 [args]
+    //  +8  descriptor
+    //  +0  returnAddress (pushed by this function, caller sets as lr)
+    //
+    //  We're aligned to an exit frame, so link it up.
+    masm.enterExitFrame(&f);
+    masm.loadJSContext(reg_cx);
+
+    // Save the current stack pointer as the base for copying arguments.
+    Register argsBase = InvalidReg;
+    if (f.explicitArgs) {
+        // argsBase can't be an argument register. Bad things would happen if
+        // the MoveResolver didn't throw an assertion failure first.
+        argsBase = r8;
+        regs.take(argsBase);
+        masm.Add(ARMRegister(argsBase, 64), masm.GetStackPointer64(),
+                 Operand(ExitFrameLayout::SizeWithFooter()));
+    }
+
+    // Reserve space for any outparameter.
+    Register outReg = InvalidReg;
+    switch (f.outParam) {
+      case Type_Value:
+        outReg = regs.takeAny();
+        masm.reserveStack(sizeof(Value));
+        masm.moveStackPtrTo(outReg);
+        break;
+
+      case Type_Handle:
+        outReg = regs.takeAny();
+        masm.PushEmptyRooted(f.outParamRootType);
+        masm.moveStackPtrTo(outReg);
+        break;
+
+      case Type_Int32:
+      case Type_Bool:
+        outReg = regs.takeAny();
+        masm.reserveStack(sizeof(int64_t));
+        masm.moveStackPtrTo(outReg);
+        break;
+
+      case Type_Double:
+        outReg = regs.takeAny();
+        masm.reserveStack(sizeof(double));
+        masm.moveStackPtrTo(outReg);
+        break;
+
+      case Type_Pointer:
+        outReg = regs.takeAny();
+        masm.reserveStack(sizeof(uintptr_t));
+        masm.moveStackPtrTo(outReg);
+        break;
+
+      default:
+        MOZ_ASSERT(f.outParam == Type_Void);
+        break;
+    }
+
+    if (!generateTLEnterVM(cx, masm, f))
+        return nullptr;
+
+    masm.setupUnalignedABICall(regs.getAny());
+    masm.passABIArg(reg_cx);
+
+    size_t argDisp = 0;
+
+    // Copy arguments.
+    for (uint32_t explicitArg = 0; explicitArg < f.explicitArgs; explicitArg++) {
+        MoveOperand from;
+        switch (f.argProperties(explicitArg)) {
+          case VMFunction::WordByValue:
+            masm.passABIArg(MoveOperand(argsBase, argDisp),
+                            (f.argPassedInFloatReg(explicitArg) ? MoveOp::DOUBLE : MoveOp::GENERAL));
+            argDisp += sizeof(void*);
+            break;
+
+          case VMFunction::WordByRef:
+            masm.passABIArg(MoveOperand(argsBase, argDisp, MoveOperand::EFFECTIVE_ADDRESS),
+                            MoveOp::GENERAL);
+            argDisp += sizeof(void*);
+            break;
+
+          case VMFunction::DoubleByValue:
+          case VMFunction::DoubleByRef:
+            MOZ_CRASH("NYI: AArch64 callVM should not be used with 128bit values.");
+        }
+    }
+
+    // Copy the semi-implicit outparam, if any.
+    // It is not a C++-abi outparam, which would get passed in the
+    // outparam register, but a real parameter to the function, which
+    // was stack-allocated above.
+    if (outReg != InvalidReg)
+        masm.passABIArg(outReg);
+
+    masm.callWithABI(f.wrapped);
+
+    if (!generateTLExitVM(cx, masm, f))
+        return nullptr;
+
+    // SP is used to transfer stack across call boundaries.
+    if (!masm.GetStackPointer64().Is(vixl::sp))
+        masm.Mov(masm.GetStackPointer64(), vixl::sp);
+
+    // Test for failure.
+    switch (f.failType()) {
+      case Type_Object:
+        masm.branchTestPtr(Assembler::Zero, r0, r0, masm.failureLabel());
+        break;
+      case Type_Bool:
+        masm.branchIfFalseBool(r0, masm.failureLabel());
+        break;
+      default:
+        MOZ_CRASH("unknown failure kind");
+    }
+
+    // Load the outparam and free any allocated stack.
+    switch (f.outParam) {
+      case Type_Value:
+        masm.Ldr(ARMRegister(JSReturnReg, 64), MemOperand(masm.GetStackPointer64()));
+        masm.freeStack(sizeof(Value));
+        break;
+
+      case Type_Handle:
+        masm.popRooted(f.outParamRootType, ReturnReg, JSReturnOperand);
+        break;
+
+      case Type_Int32:
+        masm.Ldr(ARMRegister(ReturnReg, 32), MemOperand(masm.GetStackPointer64()));
+        masm.freeStack(sizeof(int64_t));
+        break;
+
+      case Type_Bool:
+        masm.Ldrb(ARMRegister(ReturnReg, 32), MemOperand(masm.GetStackPointer64()));
+        masm.freeStack(sizeof(int64_t));
+        break;
+
+      case Type_Double:
+        MOZ_ASSERT(cx->runtime()->jitSupportsFloatingPoint);
+        masm.Ldr(ARMFPRegister(ReturnDoubleReg, 64), MemOperand(masm.GetStackPointer64()));
+        masm.freeStack(sizeof(double));
+        break;
+
+      case Type_Pointer:
+        masm.Ldr(ARMRegister(ReturnReg, 64), MemOperand(masm.GetStackPointer64()));
+        masm.freeStack(sizeof(uintptr_t));
+        break;
+
+      default:
+        MOZ_ASSERT(f.outParam == Type_Void);
+        break;
+    }
+
+    masm.leaveExitFrame();
+    masm.retn(Imm32(sizeof(ExitFrameLayout) +
+              f.explicitStackSlots() * sizeof(void*) +
+              f.extraValuesToPop * sizeof(Value)));
+
+    Linker linker(masm);
+    AutoFlushICache afc("VMWrapper");
+    JitCode* wrapper = linker.newCode<NoGC>(cx, OTHER_CODE);
+    if (!wrapper)
+        return nullptr;
+
+#ifdef JS_ION_PERF
+    writePerfSpewerJitCodeProfile(wrapper, "VMWrapper");
+#endif
+
+    // linker.newCode may trigger a GC and sweep functionWrappers_ so we have to
+    // use relookupOrAdd instead of add.
+    if (!functionWrappers_->relookupOrAdd(p, &f, wrapper))
+        return nullptr;
+
+    return wrapper;
+}
+
+JitCode*
+JitRuntime::generatePreBarrier(JSContext* cx, MIRType type)
+{
+    MacroAssembler masm(cx);
+
+    LiveRegisterSet regs = LiveRegisterSet(GeneralRegisterSet(Registers::VolatileMask),
+                                           FloatRegisterSet(FloatRegisters::VolatileMask));
+
+    // Also preserve the return address.
+    regs.add(lr);
+
+    masm.PushRegsInMask(regs);
+
+    MOZ_ASSERT(PreBarrierReg == r1);
+    masm.movePtr(ImmPtr(cx->runtime()), r3);
+
+    masm.setupUnalignedABICall(r0);
+    masm.passABIArg(r3);
+    masm.passABIArg(PreBarrierReg);
+    masm.callWithABI(IonMarkFunction(type));
+
+    // Pop the volatile regs and restore LR.
+    masm.PopRegsInMask(regs);
+
+    masm.abiret();
+
+    Linker linker(masm);
+    AutoFlushICache afc("PreBarrier");
+    return linker.newCode<NoGC>(cx, OTHER_CODE);
+}
+
+typedef bool (*HandleDebugTrapFn)(JSContext*, BaselineFrame*, uint8_t*, bool*);
+static const VMFunction HandleDebugTrapInfo =
+    FunctionInfo<HandleDebugTrapFn>(HandleDebugTrap, "HandleDebugTrap");
+
+JitCode*
+JitRuntime::generateDebugTrapHandler(JSContext* cx)
+{
+    MacroAssembler masm(cx);
+#ifndef JS_USE_LINK_REGISTER
+    // The first value contains the return addres,
+    // which we pull into ICTailCallReg for tail calls.
+    masm.setFramePushed(sizeof(intptr_t));
+#endif
+
+    Register scratch1 = r0;
+    Register scratch2 = r1;
+
+    // Load BaselineFrame pointer into scratch1.
+    masm.Sub(ARMRegister(scratch1, 64), BaselineFrameReg64, Operand(BaselineFrame::Size()));
+
+    // Enter a stub frame and call the HandleDebugTrap VM function. Ensure the
+    // stub frame has a nullptr ICStub pointer, since this pointer is marked
+    // during GC.
+    masm.movePtr(ImmPtr(nullptr), ICStubReg);
+    EmitBaselineEnterStubFrame(masm, scratch2);
+
+    JitCode* code = cx->runtime()->jitRuntime()->getVMWrapper(HandleDebugTrapInfo);
+    if (!code)
+        return nullptr;
+
+    masm.asVIXL().Push(vixl::lr, ARMRegister(scratch1, 64));
+    EmitBaselineCallVM(code, masm);
+
+    EmitBaselineLeaveStubFrame(masm);
+
+    // If the stub returns |true|, we have to perform a forced return (return
+    // from the JS frame). If the stub returns |false|, just return from the
+    // trap stub so that execution continues at the current pc.
+    Label forcedReturn;
+    masm.branchTest32(Assembler::NonZero, ReturnReg, ReturnReg, &forcedReturn);
+    masm.abiret();
+
+    masm.bind(&forcedReturn);
+    masm.loadValue(Address(BaselineFrameReg, BaselineFrame::reverseOffsetOfReturnValue()),
+                   JSReturnOperand);
+    masm.Mov(masm.GetStackPointer64(), BaselineFrameReg64);
+
+    masm.pop(BaselineFrameReg, lr);
+    masm.syncStackPtr();
+    masm.abiret();
+
+    Linker linker(masm);
+    AutoFlushICache afc("DebugTrapHandler");
+    JitCode* codeDbg = linker.newCode<NoGC>(cx, OTHER_CODE);
+
+#ifdef JS_ION_PERF
+    writePerfSpewerJitCodeProfile(codeDbg, "DebugTrapHandler");
+#endif
+
+    return codeDbg;
+}
+
+JitCode*
+JitRuntime::generateExceptionTailStub(JSContext* cx, void* handler)
+{
+    MacroAssembler masm(cx);
+
+    masm.handleFailureWithHandlerTail(handler);
+
+    Linker linker(masm);
+    AutoFlushICache afc("ExceptionTailStub");
+    JitCode* code = linker.newCode<NoGC>(cx, OTHER_CODE);
+
+#ifdef JS_ION_PERF
+    writePerfSpewerJitCodeProfile(code, "ExceptionTailStub");
+#endif
+
+    return code;
+}
+
+JitCode*
+JitRuntime::generateBailoutTailStub(JSContext* cx)
+{
+    MacroAssembler masm(cx);
+
+    masm.generateBailoutTail(r1, r2);
+
+    Linker linker(masm);
+    AutoFlushICache afc("BailoutTailStub");
+    JitCode* code = linker.newCode<NoGC>(cx, OTHER_CODE);
+
+#ifdef JS_ION_PERF
+    writePerfSpewerJitCodeProfile(code, "BailoutTailStub");
+#endif
+
+    return code;
+}
+JitCode*
+JitRuntime::generateProfilerExitFrameTailStub(JSContext* cx)
+{
+    MacroAssembler masm;
+
+    Register scratch1 = r8;
+    Register scratch2 = r9;
+    Register scratch3 = r10;
+    Register scratch4 = r11;
+
+    //
+    // The code generated below expects that the current stack pointer points
+    // to an Ion or Baseline frame, at the state it would be immediately
+    // before a ret().  Thus, after this stub's business is done, it executes
+    // a ret() and returns directly to the caller script, on behalf of the
+    // callee script that jumped to this code.
+    //
+    // Thus the expected stack is:
+    //
+    //                                   StackPointer ----+
+    //                                                    v
+    // ..., ActualArgc, CalleeToken, Descriptor, ReturnAddr
+    // MEM-HI                                       MEM-LOW
+    //
+    //
+    // The generated jitcode is responsible for overwriting the
+    // jitActivation->lastProfilingFrame field with a pointer to the previous
+    // Ion or Baseline jit-frame that was pushed before this one. It is also
+    // responsible for overwriting jitActivation->lastProfilingCallSite with
+    // the return address into that frame.  The frame could either be an
+    // immediate "caller" frame, or it could be a frame in a previous
+    // JitActivation (if the current frame was entered from C++, and the C++
+    // was entered by some caller jit-frame further down the stack).
+    //
+    // So this jitcode is responsible for "walking up" the jit stack, finding
+    // the previous Ion or Baseline JS frame, and storing its address and the
+    // return address into the appropriate fields on the current jitActivation.
+    //
+    // There are a fixed number of different path types that can lead to the
+    // current frame, which is either a baseline or ion frame:
+    //
+    // <Baseline-Or-Ion>
+    // ^
+    // |
+    // ^--- Ion
+    // |
+    // ^--- Baseline Stub <---- Baseline
+    // |
+    // ^--- Argument Rectifier
+    // |    ^
+    // |    |
+    // |    ^--- Ion
+    // |    |
+    // |    ^--- Baseline Stub <---- Baseline
+    // |
+    // ^--- Entry Frame (From C++)
+    //
+    Register actReg = scratch4;
+    AbsoluteAddress activationAddr(GetJitContext()->runtime->addressOfProfilingActivation());
+    masm.loadPtr(activationAddr, actReg);
+
+    Address lastProfilingFrame(actReg, JitActivation::offsetOfLastProfilingFrame());
+    Address lastProfilingCallSite(actReg, JitActivation::offsetOfLastProfilingCallSite());
+
+#ifdef DEBUG
+    // Ensure that frame we are exiting is current lastProfilingFrame
+    {
+        masm.loadPtr(lastProfilingFrame, scratch1);
+        Label checkOk;
+        masm.branchPtr(Assembler::Equal, scratch1, ImmWord(0), &checkOk);
+        masm.branchStackPtr(Assembler::Equal, scratch1, &checkOk);
+        masm.assumeUnreachable("Mismatch between stored lastProfilingFrame and current stack pointer.");
+        masm.bind(&checkOk);
+    }
+#endif
+
+    // Load the frame descriptor into |scratch1|, figure out what to do depending on its type.
+    masm.loadPtr(Address(masm.getStackPointer(), JitFrameLayout::offsetOfDescriptor()), scratch1);
+
+    // Going into the conditionals, we will have:
+    //      FrameDescriptor.size in scratch1
+    //      FrameDescriptor.type in scratch2
+    masm.and32(Imm32((1 << FRAMETYPE_BITS) - 1), scratch1, scratch2);
+    masm.rshiftPtr(Imm32(FRAMESIZE_SHIFT), scratch1);
+
+    // Handling of each case is dependent on FrameDescriptor.type
+    Label handle_IonJS;
+    Label handle_BaselineStub;
+    Label handle_Rectifier;
+    Label handle_IonAccessorIC;
+    Label handle_Entry;
+    Label end;
+
+    masm.branch32(Assembler::Equal, scratch2, Imm32(JitFrame_IonJS), &handle_IonJS);
+    masm.branch32(Assembler::Equal, scratch2, Imm32(JitFrame_BaselineJS), &handle_IonJS);
+    masm.branch32(Assembler::Equal, scratch2, Imm32(JitFrame_BaselineStub), &handle_BaselineStub);
+    masm.branch32(Assembler::Equal, scratch2, Imm32(JitFrame_Rectifier), &handle_Rectifier);
+    masm.branch32(Assembler::Equal, scratch2, Imm32(JitFrame_IonAccessorIC), &handle_IonAccessorIC);
+    masm.branch32(Assembler::Equal, scratch2, Imm32(JitFrame_Entry), &handle_Entry);
+
+    masm.assumeUnreachable("Invalid caller frame type when exiting from Ion frame.");
+
+    //
+    // JitFrame_IonJS
+    //
+    // Stack layout:
+    //                  ...
+    //                  Ion-Descriptor
+    //     Prev-FP ---> Ion-ReturnAddr
+    //                  ... previous frame data ... |- Descriptor.Size
+    //                  ... arguments ...           |
+    //                  ActualArgc          |
+    //                  CalleeToken         |- JitFrameLayout::Size()
+    //                  Descriptor          |
+    //        FP -----> ReturnAddr          |
+    //
+    masm.bind(&handle_IonJS);
+    {
+        // |scratch1| contains Descriptor.size
+
+        // returning directly to an IonJS frame.  Store return addr to frame
+        // in lastProfilingCallSite.
+        masm.loadPtr(Address(masm.getStackPointer(), JitFrameLayout::offsetOfReturnAddress()),
+                     scratch2);
+        masm.storePtr(scratch2, lastProfilingCallSite);
+
+        // Store return frame in lastProfilingFrame.
+        // scratch2 := masm.getStackPointer() + Descriptor.size*1 + JitFrameLayout::Size();
+        masm.addPtr(masm.getStackPointer(), scratch1, scratch2);
+        masm.syncStackPtr();
+        masm.addPtr(Imm32(JitFrameLayout::Size()), scratch2, scratch2);
+        masm.storePtr(scratch2, lastProfilingFrame);
+        masm.ret();
+    }
+
+    //
+    // JitFrame_BaselineStub
+    //
+    // Look past the stub and store the frame pointer to
+    // the baselineJS frame prior to it.
+    //
+    // Stack layout:
+    //              ...
+    //              BL-Descriptor
+    // Prev-FP ---> BL-ReturnAddr
+    //      +-----> BL-PrevFramePointer
+    //      |       ... BL-FrameData ...
+    //      |       BLStub-Descriptor
+    //      |       BLStub-ReturnAddr
+    //      |       BLStub-StubPointer          |
+    //      +------ BLStub-SavedFramePointer    |- Descriptor.Size
+    //              ... arguments ...           |
+    //              ActualArgc          |
+    //              CalleeToken         |- JitFrameLayout::Size()
+    //              Descriptor          |
+    //    FP -----> ReturnAddr          |
+    //
+    // We take advantage of the fact that the stub frame saves the frame
+    // pointer pointing to the baseline frame, so a bunch of calculation can
+    // be avoided.
+    //
+    masm.bind(&handle_BaselineStub);
+    {
+        masm.addPtr(masm.getStackPointer(), scratch1, scratch3);
+        masm.syncStackPtr();
+        Address stubFrameReturnAddr(scratch3,
+                                    JitFrameLayout::Size() +
+                                    BaselineStubFrameLayout::offsetOfReturnAddress());
+        masm.loadPtr(stubFrameReturnAddr, scratch2);
+        masm.storePtr(scratch2, lastProfilingCallSite);
+
+        Address stubFrameSavedFramePtr(scratch3,
+                                       JitFrameLayout::Size() - (2 * sizeof(void*)));
+        masm.loadPtr(stubFrameSavedFramePtr, scratch2);
+        masm.addPtr(Imm32(sizeof(void*)), scratch2); // Skip past BL-PrevFramePtr.
+        masm.storePtr(scratch2, lastProfilingFrame);
+        masm.ret();
+    }
+
+
+    //
+    // JitFrame_Rectifier
+    //
+    // The rectifier frame can be preceded by either an IonJS or a
+    // BaselineStub frame.
+    //
+    // Stack layout if caller of rectifier was Ion:
+    //
+    //              Ion-Descriptor
+    //              Ion-ReturnAddr
+    //              ... ion frame data ... |- Rect-Descriptor.Size
+    //              < COMMON LAYOUT >
+    //
+    // Stack layout if caller of rectifier was Baseline:
+    //
+    //              BL-Descriptor
+    // Prev-FP ---> BL-ReturnAddr
+    //      +-----> BL-SavedFramePointer
+    //      |       ... baseline frame data ...
+    //      |       BLStub-Descriptor
+    //      |       BLStub-ReturnAddr
+    //      |       BLStub-StubPointer          |
+    //      +------ BLStub-SavedFramePointer    |- Rect-Descriptor.Size
+    //              ... args to rectifier ...   |
+    //              < COMMON LAYOUT >
+    //
+    // Common stack layout:
+    //
+    //              ActualArgc          |
+    //              CalleeToken         |- IonRectitiferFrameLayout::Size()
+    //              Rect-Descriptor     |
+    //              Rect-ReturnAddr     |
+    //              ... rectifier data & args ... |- Descriptor.Size
+    //              ActualArgc      |
+    //              CalleeToken     |- JitFrameLayout::Size()
+    //              Descriptor      |
+    //    FP -----> ReturnAddr      |
+    //
+    masm.bind(&handle_Rectifier);
+    {
+        // scratch2 := StackPointer + Descriptor.size*1 + JitFrameLayout::Size();
+        masm.addPtr(masm.getStackPointer(), scratch1, scratch2);
+        masm.syncStackPtr();
+        masm.add32(Imm32(JitFrameLayout::Size()), scratch2);
+        masm.loadPtr(Address(scratch2, RectifierFrameLayout::offsetOfDescriptor()), scratch3);
+        masm.rshiftPtr(Imm32(FRAMESIZE_SHIFT), scratch3, scratch1);
+        masm.and32(Imm32((1 << FRAMETYPE_BITS) - 1), scratch3);
+
+        // Now |scratch1| contains Rect-Descriptor.Size
+        // and |scratch2| points to Rectifier frame
+        // and |scratch3| contains Rect-Descriptor.Type
+
+        // Check for either Ion or BaselineStub frame.
+        Label handle_Rectifier_BaselineStub;
+        masm.branch32(Assembler::NotEqual, scratch3, Imm32(JitFrame_IonJS),
+                      &handle_Rectifier_BaselineStub);
+
+        // Handle Rectifier <- IonJS
+        // scratch3 := RectFrame[ReturnAddr]
+        masm.loadPtr(Address(scratch2, RectifierFrameLayout::offsetOfReturnAddress()), scratch3);
+        masm.storePtr(scratch3, lastProfilingCallSite);
+
+        // scratch3 := RectFrame + Rect-Descriptor.Size + RectifierFrameLayout::Size()
+        masm.addPtr(scratch2, scratch1, scratch3);
+        masm.add32(Imm32(RectifierFrameLayout::Size()), scratch3);
+        masm.storePtr(scratch3, lastProfilingFrame);
+        masm.ret();
+
+        // Handle Rectifier <- BaselineStub <- BaselineJS
+        masm.bind(&handle_Rectifier_BaselineStub);
+#ifdef DEBUG
+        {
+            Label checkOk;
+            masm.branch32(Assembler::Equal, scratch3, Imm32(JitFrame_BaselineStub), &checkOk);
+            masm.assumeUnreachable("Unrecognized frame preceding baselineStub.");
+            masm.bind(&checkOk);
+        }
+#endif
+        masm.addPtr(scratch2, scratch1, scratch3);
+        Address stubFrameReturnAddr(scratch3, RectifierFrameLayout::Size() +
+                                              BaselineStubFrameLayout::offsetOfReturnAddress());
+        masm.loadPtr(stubFrameReturnAddr, scratch2);
+        masm.storePtr(scratch2, lastProfilingCallSite);
+
+        Address stubFrameSavedFramePtr(scratch3,
+                                       RectifierFrameLayout::Size() - (2 * sizeof(void*)));
+        masm.loadPtr(stubFrameSavedFramePtr, scratch2);
+        masm.addPtr(Imm32(sizeof(void*)), scratch2);
+        masm.storePtr(scratch2, lastProfilingFrame);
+        masm.ret();
+    }
+
+    // JitFrame_IonAccessorIC
+    //
+    // The caller is always an IonJS frame.
+    //
+    //              Ion-Descriptor
+    //              Ion-ReturnAddr
+    //              ... ion frame data ... |- AccFrame-Descriptor.Size
+    //              StubCode             |
+    //              AccFrame-Descriptor  |- IonAccessorICFrameLayout::Size()
+    //              AccFrame-ReturnAddr  |
+    //              ... accessor frame data & args ... |- Descriptor.Size
+    //              ActualArgc      |
+    //              CalleeToken     |- JitFrameLayout::Size()
+    //              Descriptor      |
+    //    FP -----> ReturnAddr      |
+    masm.bind(&handle_IonAccessorIC);
+    {
+        // scratch2 := StackPointer + Descriptor.size + JitFrameLayout::Size()
+        masm.addPtr(masm.getStackPointer(), scratch1, scratch2);
+        masm.syncStackPtr();
+        masm.addPtr(Imm32(JitFrameLayout::Size()), scratch2);
+
+        // scratch3 := AccFrame-Descriptor.Size
+        masm.loadPtr(Address(scratch2, IonAccessorICFrameLayout::offsetOfDescriptor()), scratch3);
+#ifdef DEBUG
+        // Assert previous frame is an IonJS frame.
+        masm.movePtr(scratch3, scratch1);
+        masm.and32(Imm32((1 << FRAMETYPE_BITS) - 1), scratch1);
+        {
+            Label checkOk;
+            masm.branch32(Assembler::Equal, scratch1, Imm32(JitFrame_IonJS), &checkOk);
+            masm.assumeUnreachable("IonAccessorIC frame must be preceded by IonJS frame");
+            masm.bind(&checkOk);
+        }
+#endif
+        masm.rshiftPtr(Imm32(FRAMESIZE_SHIFT), scratch3);
+
+        // lastProfilingCallSite := AccFrame-ReturnAddr
+        masm.loadPtr(Address(scratch2, IonAccessorICFrameLayout::offsetOfReturnAddress()), scratch1);
+        masm.storePtr(scratch1, lastProfilingCallSite);
+
+        // lastProfilingFrame := AccessorFrame + AccFrame-Descriptor.Size +
+        //                       IonAccessorICFrameLayout::Size()
+        masm.addPtr(scratch2, scratch3, scratch1);
+        masm.addPtr(Imm32(IonAccessorICFrameLayout::Size()), scratch1);
+        masm.storePtr(scratch1, lastProfilingFrame);
+        masm.ret();
+    }
+
+    //
+    // JitFrame_Entry
+    //
+    // If at an entry frame, store null into both fields.
+    //
+    masm.bind(&handle_Entry);
+    {
+        masm.movePtr(ImmPtr(nullptr), scratch1);
+        masm.storePtr(scratch1, lastProfilingCallSite);
+        masm.storePtr(scratch1, lastProfilingFrame);
+        masm.ret();
+    }
+
+    Linker linker(masm);
+    AutoFlushICache afc("ProfilerExitFrameTailStub");
+    JitCode* code = linker.newCode<NoGC>(cx, OTHER_CODE);
+
+#ifdef JS_ION_PERF
+    writePerfSpewerJitCodeProfile(code, "ProfilerExitFrameStub");
+#endif
+
+    return code;
+}