# HG changeset patch

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

# Date 1519822672 -3600

# Node ID 800abe66894d6b07b24bccecbf6a65e2261076f6

# Parent  223c97459e96183eb616aed39147207bdb953ba8

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

@@ -90,17 +90,25 @@ UnboxedLayout::makeConstructorCode(JSCon

     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);

@@ -228,17 +236,32 @@ UnboxedLayout::makeConstructorCode(JSCon

     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);