diff -r 87c1625d07e2 -r 7a49806c8dae mozilla-bmo1375074.patch
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mozilla-bmo1375074.patch	Fri Jun 08 22:09:15 2018 +0200
@@ -0,0 +1,95 @@
+
+# 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);
+ 
+