# HG changeset patch
# User Lars T Hansen <lhansen@mozilla.com>
# Date 1519822672 -3600
# Node ID 800abe66894d6b07b24bccecbf6a65e2261076f6
# Parent  6fbe9ec020d822b1deef5b0afe76b905b82308a1
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);