diff --git a/xen/common/efi/efi.h b/xen/common/efi/efi.h
index c557104abc..9fe6ff16b0 100644
--- a/xen/common/efi/efi.h
+++ b/xen/common/efi/efi.h
@@ -36,6 +36,3 @@ extern const struct efi_pci_rom *efi_pci_roms;
 
 extern UINT64 efi_boot_max_var_store_size, efi_boot_remain_var_store_size,
               efi_boot_max_var_size;
-
-unsigned long efi_rs_enter(void);
-void efi_rs_leave(unsigned long);
diff --git a/xen/common/efi/runtime.c b/xen/common/efi/runtime.c
index ae875570fb..b10b15e523 100644
--- a/xen/common/efi/runtime.c
+++ b/xen/common/efi/runtime.c
@@ -8,6 +8,25 @@
 
 DEFINE_XEN_GUEST_HANDLE(CHAR16);
 
+struct efi_rs_state {
+#ifdef CONFIG_X86
+ /*
+  * The way stacks get set up leads to them always being on an 8-byte
+  * boundary not evenly divisible by 16 (see asm-x86/current.h). The EFI ABI,
+  * just like the CPU one, however requires stacks to be 16-byte aligned
+  * before every function call. Since the compiler assumes this (unless
+  * passing it -mpreferred-stack-boundary=3), it wouldn't generate code to
+  * align the stack to 16 bytes even if putting a 16-byte aligned object
+  * there. Hence we need to force larger than 16-byte alignment, even if we
+  * don't strictly need that.
+  */
+ unsigned long __aligned(32) cr3;
+#endif
+};
+
+struct efi_rs_state efi_rs_enter(void);
+void efi_rs_leave(struct efi_rs_state *);
+
 #ifndef COMPAT
 
 #ifdef CONFIG_ARM  /* Disabled until runtime services implemented */
@@ -52,17 +71,19 @@ struct efi __read_mostly efi = {
 const struct efi_pci_rom *__read_mostly efi_pci_roms;
 
 #ifndef CONFIG_ARM /* TODO - disabled until implemented on ARM */
-unsigned long efi_rs_enter(void)
+
+struct efi_rs_state efi_rs_enter(void)
 {
     static const u16 fcw = FCW_DEFAULT;
     static const u32 mxcsr = MXCSR_DEFAULT;
-    unsigned long cr3 = read_cr3();
+    struct efi_rs_state state = { .cr3 = 0 };
 
     if ( !efi_l4_pgtable )
-        return 0;
+        return state;
 
+    state.cr3 = read_cr3();
     save_fpu_enable();
-    asm volatile ( "fldcw %0" :: "m" (fcw) );
+    asm volatile ( "fnclex; fldcw %0" :: "m" (fcw) );
     asm volatile ( "ldmxcsr %0" :: "m" (mxcsr) );
 
     spin_lock(&efi_rs_lock);
@@ -85,14 +106,14 @@ unsigned long efi_rs_enter(void)
 
     write_cr3(virt_to_maddr(efi_l4_pgtable));
 
-    return cr3;
+    return state;
 }
 
-void efi_rs_leave(unsigned long cr3)
+void efi_rs_leave(struct efi_rs_state *state)
 {
-    if ( !cr3 )
+    if ( !state->cr3 )
         return;
-    write_cr3(cr3);
+    write_cr3(state->cr3);
     if ( is_pv_vcpu(current) && !is_idle_vcpu(current) )
     {
         struct desc_ptr gdt_desc = {
@@ -119,14 +140,15 @@ unsigned long efi_get_time(void)
 {
     EFI_TIME time;
     EFI_STATUS status;
-    unsigned long cr3 = efi_rs_enter(), flags;
+    struct efi_rs_state state = efi_rs_enter();
+    unsigned long flags;
 
-    if ( !cr3 )
+    if ( !state.cr3 )
         return 0;
     spin_lock_irqsave(&rtc_lock, flags);
     status = efi_rs->GetTime(&time, NULL);
     spin_unlock_irqrestore(&rtc_lock, flags);
-    efi_rs_leave(cr3);
+    efi_rs_leave(&state);
 
     if ( EFI_ERROR(status) )
         return 0;
@@ -138,12 +160,12 @@ unsigned long efi_get_time(void)
 void efi_halt_system(void)
 {
     EFI_STATUS status;
-    unsigned long cr3 = efi_rs_enter();
+    struct efi_rs_state state = efi_rs_enter();
 
-    if ( !cr3 )
+    if ( !state.cr3 )
         return;
     status = efi_rs->ResetSystem(EfiResetShutdown, EFI_SUCCESS, 0, NULL);
-    efi_rs_leave(cr3);
+    efi_rs_leave(&state);
 
     printk(XENLOG_WARNING "EFI: could not halt system (%#lx)\n", status);
 }
@@ -151,13 +173,13 @@ void efi_halt_system(void)
 void efi_reset_system(bool_t warm)
 {
     EFI_STATUS status;
-    unsigned long cr3 = efi_rs_enter();
+    struct efi_rs_state state = efi_rs_enter();
 
-    if ( !cr3 )
+    if ( !state.cr3 )
         return;
     status = efi_rs->ResetSystem(warm ? EfiResetWarm : EfiResetCold,
                                  EFI_SUCCESS, 0, NULL);
-    efi_rs_leave(cr3);
+    efi_rs_leave(&state);
 
     printk(XENLOG_WARNING "EFI: could not reset system (%#lx)\n", status);
 }
@@ -177,12 +199,12 @@ int efi_get_info(uint32_t idx, union xenpf_efi_info *info)
         break;
     case XEN_FW_EFI_RT_VERSION:
     {
-        unsigned long cr3 = efi_rs_enter();
+        struct efi_rs_state state = efi_rs_enter();
 
-        if ( !cr3 )
+        if ( !state.cr3 )
             return -EOPNOTSUPP;
         info->version = efi_rs->Hdr.Revision;
-        efi_rs_leave(cr3);
+        efi_rs_leave(&state);
         break;
     }
     case XEN_FW_EFI_CONFIG_TABLE:
@@ -300,7 +322,8 @@ static inline EFI_GUID *cast_guid(struct xenpf_efi_guid *guid)
 
 int efi_runtime_call(struct xenpf_efi_runtime_call *op)
 {
-    unsigned long cr3, flags;
+    struct efi_rs_state state;
+    unsigned long flags;
     EFI_STATUS status = EFI_NOT_STARTED;
     int rc = 0;
 
@@ -313,13 +336,13 @@ int efi_runtime_call(struct xenpf_efi_runtime_call *op)
         if ( op->misc )
             return -EINVAL;
 
-        cr3 = efi_rs_enter();
-        if ( !cr3 )
+        state = efi_rs_enter();
+        if ( !state.cr3 )
             return -EOPNOTSUPP;
         spin_lock_irqsave(&rtc_lock, flags);
         status = efi_rs->GetTime(cast_time(&op->u.get_time.time), &caps);
         spin_unlock_irqrestore(&rtc_lock, flags);
-        efi_rs_leave(cr3);
+        efi_rs_leave(&state);
 
         if ( !EFI_ERROR(status) )
         {
@@ -335,13 +358,13 @@ int efi_runtime_call(struct xenpf_efi_runtime_call *op)
         if ( op->misc )
             return -EINVAL;
 
-        cr3 = efi_rs_enter();
-        if ( !cr3 )
+        state = efi_rs_enter();
+        if ( !state.cr3 )
             return -EOPNOTSUPP;
         spin_lock_irqsave(&rtc_lock, flags);
         status = efi_rs->SetTime(cast_time(&op->u.set_time));
         spin_unlock_irqrestore(&rtc_lock, flags);
-        efi_rs_leave(cr3);
+        efi_rs_leave(&state);
         break;
 
     case XEN_EFI_get_wakeup_time:
@@ -351,14 +374,14 @@ int efi_runtime_call(struct xenpf_efi_runtime_call *op)
         if ( op->misc )
             return -EINVAL;
 
-        cr3 = efi_rs_enter();
-        if ( !cr3 )
+        state = efi_rs_enter();
+        if ( !state.cr3 )
             return -EOPNOTSUPP;
         spin_lock_irqsave(&rtc_lock, flags);
         status = efi_rs->GetWakeupTime(&enabled, &pending,
                                        cast_time(&op->u.get_wakeup_time));
         spin_unlock_irqrestore(&rtc_lock, flags);
-        efi_rs_leave(cr3);
+        efi_rs_leave(&state);
 
         if ( !EFI_ERROR(status) )
         {
@@ -375,8 +398,8 @@ int efi_runtime_call(struct xenpf_efi_runtime_call *op)
                           XEN_EFI_SET_WAKEUP_TIME_ENABLE_ONLY) )
             return -EINVAL;
 
-        cr3 = efi_rs_enter();
-        if ( !cr3 )
+        state = efi_rs_enter();
+        if ( !state.cr3 )
             return -EOPNOTSUPP;
         spin_lock_irqsave(&rtc_lock, flags);
         status = efi_rs->SetWakeupTime(!!(op->misc &
@@ -386,7 +409,7 @@ int efi_runtime_call(struct xenpf_efi_runtime_call *op)
                                        NULL :
                                        cast_time(&op->u.set_wakeup_time));
         spin_unlock_irqrestore(&rtc_lock, flags);
-        efi_rs_leave(cr3);
+        efi_rs_leave(&state);
 
         op->misc = 0;
         break;
@@ -395,12 +418,12 @@ int efi_runtime_call(struct xenpf_efi_runtime_call *op)
         if ( op->misc )
             return -EINVAL;
 
-        cr3 = efi_rs_enter();
-        if ( cr3 )
+        state = efi_rs_enter();
+        if ( state.cr3 )
             status = efi_rs->GetNextHighMonotonicCount(&op->misc);
         else
             rc = -EOPNOTSUPP;
-        efi_rs_leave(cr3);
+        efi_rs_leave(&state);
         break;
 
     case XEN_EFI_get_variable:
@@ -434,13 +457,13 @@ int efi_runtime_call(struct xenpf_efi_runtime_call *op)
         else
             data = NULL;
 
-        cr3 = efi_rs_enter();
-        if ( cr3 )
+        state = efi_rs_enter();
+        if ( state.cr3 )
         {
             status = efi_rs->GetVariable(
                 name, cast_guid(&op->u.get_variable.vendor_guid),
                 &op->misc, &size, data);
-            efi_rs_leave(cr3);
+            efi_rs_leave(&state);
 
             if ( !EFI_ERROR(status) &&
                  copy_to_guest(op->u.get_variable.data, data, size) )
@@ -477,14 +500,14 @@ int efi_runtime_call(struct xenpf_efi_runtime_call *op)
             rc = -EFAULT;
         else
         {
-            cr3 = efi_rs_enter();
-            if ( cr3 )
+            state = efi_rs_enter();
+            if ( state.cr3 )
                 status = efi_rs->SetVariable(
                     name, cast_guid(&op->u.set_variable.vendor_guid),
                     op->misc, op->u.set_variable.size, data);
             else
                 rc = -EOPNOTSUPP;
-            efi_rs_leave(cr3);
+            efi_rs_leave(&state);
         }
 
         xfree(data);
@@ -514,13 +537,13 @@ int efi_runtime_call(struct xenpf_efi_runtime_call *op)
             return -EFAULT;
         }
 
-        cr3 = efi_rs_enter();
-        if ( cr3 )
+        state = efi_rs_enter();
+        if ( state.cr3 )
         {
             status = efi_rs->GetNextVariableName(
                 &size, name.str,
                 cast_guid(&op->u.get_next_variable_name.vendor_guid));
-            efi_rs_leave(cr3);
+            efi_rs_leave(&state);
 
             /*
              * Copy the variable name if necessary. The caller provided size
@@ -569,10 +592,10 @@ int efi_runtime_call(struct xenpf_efi_runtime_call *op)
             break;
         }
 
-        cr3 = efi_rs_enter();
-        if ( !cr3 || (efi_rs->Hdr.Revision >> 16) < 2 )
+        state = efi_rs_enter();
+        if ( !state.cr3 || (efi_rs->Hdr.Revision >> 16) < 2 )
         {
-            efi_rs_leave(cr3);
+            efi_rs_leave(&state);
             return -EOPNOTSUPP;
         }
         status = efi_rs->QueryVariableInfo(
@@ -580,7 +603,7 @@ int efi_runtime_call(struct xenpf_efi_runtime_call *op)
             &op->u.query_variable_info.max_store_size,
             &op->u.query_variable_info.remain_store_size,
             &op->u.query_variable_info.max_size);
-        efi_rs_leave(cr3);
+        efi_rs_leave(&state);
         break;
 
     case XEN_EFI_query_capsule_capabilities:
@@ -588,13 +611,13 @@ int efi_runtime_call(struct xenpf_efi_runtime_call *op)
         if ( op->misc )
             return -EINVAL;
 
-        cr3 = efi_rs_enter();
-        if ( !cr3 || (efi_rs->Hdr.Revision >> 16) < 2 )
+        state = efi_rs_enter();
+        if ( !state.cr3 || (efi_rs->Hdr.Revision >> 16) < 2 )
         {
-            efi_rs_leave(cr3);
+            efi_rs_leave(&state);
             return -EOPNOTSUPP;
         }
-        efi_rs_leave(cr3);
+        efi_rs_leave(&state);
         /* XXX fall through for now */
     default:
         return -ENOSYS;
diff --git a/xen/include/xen/compiler.h b/xen/include/xen/compiler.h
index 4b3472daee..e6a32cef90 100644
--- a/xen/include/xen/compiler.h
+++ b/xen/include/xen/compiler.h
@@ -34,6 +34,8 @@
 #define __used_section(s) __used __attribute__((__section__(s)))
 #define __text_section(s) __attribute__((__section__(s)))
 
+#define __aligned(a) __attribute__((__aligned__(a)))
+
 #ifdef INIT_SECTIONS_ONLY
 /*
  * For sources indicated to have only init code, make sure even