i386: Simplify failsafe callback handling.

Signed-off-by: Keir Fraser <keir@xensource.com>

xen/arch/x86/x86_32/entry.S

@@ -99,17 +99,9 @@ restore_all_guest:
 .Lrestore_iret_guest:
 .Lft5:  iret
 .section .fixup,"ax"
-.Lfx1:  subl  $28,%esp
-        pushl 28(%esp)                 # error_code/entry_vector
-        movl  %eax,UREGS_eax+4(%esp)
-        movl  %ebp,UREGS_ebp+4(%esp)
-        movl  %edi,UREGS_edi+4(%esp)
-        movl  %esi,UREGS_esi+4(%esp)
-        movl  %edx,UREGS_edx+4(%esp)
-        movl  %ecx,UREGS_ecx+4(%esp)
-        movl  %ebx,UREGS_ebx+4(%esp)
-        sti
-        popl  %esi
+.Lfx1:  sti
+        SAVE_ALL_GPRS
+        mov   UREGS_error_code(%esp),%esi
         pushfl                         # EFLAGS
         movl  $__HYPERVISOR_CS,%eax
         pushl %eax                     # CS

xen/include/asm-x86/x86_32/asm_defns.h

@@ -26,6 +26,17 @@
 #define ASSERT_INTERRUPTS_ENABLED  ASSERT_INTERRUPT_STATUS(nz)
 #define ASSERT_INTERRUPTS_DISABLED ASSERT_INTERRUPT_STATUS(z)
 
+#define SAVE_ALL_GPRS                                   \
+        cld;                                            \
+        pushl %eax;                                     \
+        pushl %ebp;                                     \
+        SETUP_EXCEPTION_FRAME_POINTER;                  \
+        pushl %edi;                                     \
+        pushl %esi;                                     \
+        pushl %edx;                                     \
+        pushl %ecx;                                     \
+        pushl %ebx
+
 /*
  * Saves all register state into an exception/interrupt stack frame.
  * Returns to the caller at <xen_lbl> if the interrupted context is within
@@ -36,15 +47,7 @@
  * the caller is reponsible for validity of %ds/%es.
  */
 #define SAVE_ALL(xen_lbl, vm86_lbl)                     \
-        cld;                                            \
-        pushl %eax;                                     \
-        pushl %ebp;                                     \
-        SETUP_EXCEPTION_FRAME_POINTER;                  \
-        pushl %edi;                                     \
-        pushl %esi;                                     \
-        pushl %edx;                                     \
-        pushl %ecx;                                     \
-        pushl %ebx;                                     \
+        SAVE_ALL_GPRS;                                  \
         testl $(X86_EFLAGS_VM),UREGS_eflags(%esp);      \
         mov   %ds,%edi;                                 \
         mov   %es,%esi;                                 \