# HG changeset patch

# User Lars T Hansen <lhansen@mozilla.com>

# Date 1519822672 -3600

# Node ID 800abe66894d6b07b24bccecbf6a65e2261076f6

Bug 1375074 - Save and restore non-volatile x28 on ARM64 for generated unboxed object constructor.  r=sstangl

diff --git a/js/src/jit-test/tests/bug1375074.js b/js/src/jit-test/tests/bug1375074.js

new file mode 100644

--- /dev/null

+++ b/js/src/jit-test/tests/bug1375074.js

@@ -0,0 +1,18 @@

+// This forces the VM to start creating unboxed objects and thus stresses a

+// particular path into generated code for a specialized unboxed object

+// constructor.

+

+var K = 2000;			// 2000 should be plenty

+var s = "[";

+var i;

+for ( i=0; i < K-1; i++ )

+    s = s + `{"i":${i}},`;

+s += `{"i":${i}}]`;

+var v = JSON.parse(s);

+

+assertEq(v.length == K, true);

+

+for ( i=0; i < K; i++) {

+    assertEq(v[i] instanceof Object, true);

+    assertEq(v[i].i, i);

+}

diff --git a/js/src/vm/UnboxedObject.cpp b/js/src/vm/UnboxedObject.cpp

--- a/js/src/vm/UnboxedObject.cpp

+++ b/js/src/vm/UnboxedObject.cpp

@@ -81,18 +81,25 @@ static const uintptr_t CLEAR_CONSTRUCTOR

   masm.loadPtr(Address(masm.getStackPointer(), sizeof(void*)), propertiesReg);

   masm.loadPtr(Address(masm.getStackPointer(), 2 * sizeof(void*)), newKindReg);

 #else

   propertiesReg = IntArgReg0;

   newKindReg = IntArgReg1;

 #endif

 #ifdef JS_CODEGEN_ARM64

-  // ARM64 communicates stack address via sp, but uses a pseudo-sp for

-  // addressing.

+  // ARM64 communicates stack address via sp, but uses a pseudo-sp (PSP) for

+  // addressing.  The register we use for PSP may however also be used by

+  // calling code, and it is nonvolatile, so save it.  Do this as a special

+  // case first because the generic save/restore code needs the PSP to be

+  // initialized already.

+  MOZ_ASSERT(PseudoStackPointer64.Is(masm.GetStackPointer64()));

+  masm.Str(PseudoStackPointer64, vixl::MemOperand(sp, -16, vixl::PreIndex));

+

+  // Initialize the PSP from the SP.

   masm.initStackPtr();

 #endif

   MOZ_ASSERT(propertiesReg.volatile_());

   MOZ_ASSERT(newKindReg.volatile_());

   AllocatableGeneralRegisterSet regs(GeneralRegisterSet::All());

   regs.take(propertiesReg);

@@ -234,17 +241,32 @@ static const uintptr_t CLEAR_CONSTRUCTOR

   masm.bind(&done);

   if (object != ReturnReg) masm.movePtr(object, ReturnReg);

   // Restore non-volatile registers which were saved on entry.

   if (ScratchDoubleReg.volatile_()) masm.pop(ScratchDoubleReg);

   masm.PopRegsInMask(savedNonVolatileRegisters);

+#ifdef JS_CODEGEN_ARM64

+  // Now restore the value that was in the PSP register on entry, and return.

+

+  // Obtain the correct SP from the PSP.

+  masm.Mov(sp, PseudoStackPointer64);

+

+  // Restore the saved value of the PSP register, this value is whatever the

+  // caller had saved in it, not any actual SP value, and it must not be

+  // overwritten subsequently.

+  masm.Ldr(PseudoStackPointer64, vixl::MemOperand(sp, 16, vixl::PostIndex));

+

+  // Perform a plain Ret(), as abiret() will move SP <- PSP and that is wrong.

+  masm.Ret(vixl::lr);

+#else

   masm.abiret();

+#endif

   masm.bind(&failureStoreOther);

   // There was a failure while storing a value which cannot be stored at all

   // in the unboxed object. Initialize the object so it is safe for GC and

   // return null.

   masm.initUnboxedObjectContents(object, templateObject);