diff --git a/js/src/assembler/assembler/ARMAssembler.cpp b/js/src/assembler/assembler/ARMAssembler.cpp
index 85fbaf16b44..ba7cec282bb 100644
--- a/js/src/assembler/assembler/ARMAssembler.cpp
+++ b/js/src/assembler/assembler/ARMAssembler.cpp
@@ -201,6 +201,11 @@ int ARMAssembler::genInt(int reg, ARMWord imm, bool positive)
     return 1;
 }
 
+#ifdef __GNUC__
+// If the result of this function isn't used, the caller should probably be
+// using movImm.
+__attribute__((warn_unused_result))
+#endif
 ARMWord ARMAssembler::getImm(ARMWord imm, int tmpReg, bool invert)
 {
     ARMWord tmp;
diff --git a/js/src/assembler/assembler/ARMAssembler.h b/js/src/assembler/assembler/ARMAssembler.h
index 16b7d58f559..0f8d943cee7 100644
--- a/js/src/assembler/assembler/ARMAssembler.h
+++ b/js/src/assembler/assembler/ARMAssembler.h
@@ -929,7 +929,9 @@ namespace JSC {
 
         JmpDst label()
         {
-            return JmpDst(m_buffer.size());
+            JmpDst label(m_buffer.size());
+            js::JaegerSpew(js::JSpew_Insns, IPFX "#label     ((%d))\n", MAYBE_PAD, label.m_offset);
+            return label;
         }
 
         JmpDst align(int alignment)
@@ -1050,10 +1052,11 @@ namespace JSC {
 	    // Like repatchLoadPtrToLEA, this is specialized for our purpose.
             ARMWord* insn = reinterpret_cast<ARMWord*>(from);
 	    if ((*insn & 0x0ff00f00) == 0x05900000)
-		return;
-            ASSERT((*insn & 0xf00ff0ff) == 0x02800000);
+		return; // Valid ldr instruction
+            ASSERT((*insn & 0x0ff00000) == 0x02800000); // Valid add instruction
+            ASSERT((*insn & 0x00000f00) == 0x00000000); // Simple-to-handle immediates (no rotate)
 
-            *insn = (*insn &  0x0ff00f00) | 0x05900000;
+            *insn = (*insn &  0xf00ff0ff) | 0x05900000;
             ExecutableAllocator::cacheFlush(insn, sizeof(ARMWord));
         }
 
@@ -1087,7 +1090,7 @@ namespace JSC {
                            ISPFX "##relinkJump      ((%p)) jumps to ((%p))\n",
                            from, to);
 
-            patchPointerInternal(reinterpret_cast<intptr_t>(from) - sizeof(ARMWord), to);
+            patchPointerInternal(reinterpret_cast<intptr_t>(from), to);
         }
 
         static bool canRelinkJump(void* from, void* to)
@@ -1110,14 +1113,14 @@ namespace JSC {
                            ISPFX "##relinkCall      ((%p)) jumps to ((%p))\n",
                            from, to);
 
-            patchPointerInternal(reinterpret_cast<intptr_t>(from) - sizeof(ARMWord), to);
+            patchPointerInternal(reinterpret_cast<intptr_t>(from), to);
         }
 
         // Address operations
 
         static void* getRelocatedAddress(void* code, JmpSrc jump)
         {
-            return reinterpret_cast<void*>(reinterpret_cast<ARMWord*>(code) + jump.m_offset / sizeof(ARMWord) + 1);
+            return reinterpret_cast<void*>(reinterpret_cast<ARMWord*>(code) + jump.m_offset / sizeof(ARMWord));
         }
 
         static void* getRelocatedAddress(void* code, JmpDst label)
@@ -1129,7 +1132,7 @@ namespace JSC {
 
         static int getDifferenceBetweenLabels(JmpDst from, JmpSrc to)
         {
-            return (to.m_offset + sizeof(ARMWord)) - from.m_offset;
+            return to.m_offset - from.m_offset;
         }
 
         static int getDifferenceBetweenLabels(JmpDst from, JmpDst to)
diff --git a/js/src/assembler/assembler/MacroAssemblerARM.h b/js/src/assembler/assembler/MacroAssemblerARM.h
index 15aca15c81b..742b85c1135 100644
--- a/js/src/assembler/assembler/MacroAssemblerARM.h
+++ b/js/src/assembler/assembler/MacroAssemblerARM.h
@@ -277,6 +277,7 @@ public:
 
     DataLabel32 load32WithAddressOffsetPatch(Address address, RegisterID dest)
     {
+        ASSERT(address.base != ARMRegisters::S0);
         DataLabel32 dataLabel(this);
         m_assembler.ldr_un_imm(ARMRegisters::S0, 0);
         m_assembler.dtr_ur(true, dest, address.base, ARMRegisters::S0);
@@ -285,6 +286,8 @@ public:
 
     DataLabel32 load64WithAddressOffsetPatch(Address address, RegisterID hi, RegisterID lo)
     {
+        ASSERT(address.base != ARMRegisters::S0);
+        ASSERT(lo != ARMRegisters::S0);
         DataLabel32 dataLabel(this);
         m_assembler.ldr_un_imm(ARMRegisters::S0, 0);
         m_assembler.add_r(ARMRegisters::S0, ARMRegisters::S0, address.base);
@@ -316,6 +319,7 @@ public:
 
     DataLabel32 store32WithAddressOffsetPatch(RegisterID src, Address address)
     {
+        ASSERT(address.base != ARMRegisters::S0);
         DataLabel32 dataLabel(this);
         m_assembler.ldr_un_imm(ARMRegisters::S0, 0);
         m_assembler.dtr_ur(false, src, address.base, ARMRegisters::S0);
@@ -324,6 +328,9 @@ public:
 
     DataLabel32 store64WithAddressOffsetPatch(RegisterID hi, RegisterID lo, Address address)
     {
+        ASSERT(hi != ARMRegisters::S0);
+        ASSERT(lo != ARMRegisters::S0);
+        ASSERT(address.base != ARMRegisters::S0);
         DataLabel32 dataLabel(this);
         m_assembler.ldr_un_imm(ARMRegisters::S0, 0);
         m_assembler.add_r(ARMRegisters::S0, ARMRegisters::S0, address.base);
@@ -334,9 +341,14 @@ public:
 
     DataLabel32 store64WithAddressOffsetPatch(Imm32 hi, RegisterID lo, Address address)
     {
+        ASSERT(lo != ARMRegisters::S0);
+        ASSERT(lo != ARMRegisters::S1);
+        ASSERT(lo != address.base);
+        ASSERT(address.base != ARMRegisters::S0);
+        ASSERT(address.base != ARMRegisters::S1);
         DataLabel32 dataLabel(this);
         m_assembler.ldr_un_imm(ARMRegisters::S0, 0);
-        m_assembler.getImm(hi.m_value, ARMRegisters::S1);
+        m_assembler.moveImm(hi.m_value, ARMRegisters::S1);
         m_assembler.add_r(ARMRegisters::S0, ARMRegisters::S0, address.base);
         m_assembler.dtr_u(false, lo, ARMRegisters::S0, 0);
         m_assembler.dtr_u(false, ARMRegisters::S1, ARMRegisters::S0, 4);