x86: adjust unwind info for special HYPERVISOR_iret stack layout

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/arch/i386/kernel/head-xen.S
+++ b/arch/i386/kernel/head-xen.S
@@ -70,7 +70,13 @@ ENTRY(startup_32)
 .org HYPERCALL_PAGE_OFFSET
 ENTRY(hypercall_page)
 	CFI_STARTPROC
-.skip 0x1000
+	.skip __HYPERVISOR_iret * 32
+	CFI_REMEMBER_STATE
+	.skip 1 /* push %eax */
+	CFI_ADJUST_CFA_OFFSET	8
+	CFI_REL_OFFSET	eax,0
+	CFI_RESTORE_STATE
+	.balign 0x1000,0
 	CFI_ENDPROC
 
 /*
--- a/arch/x86_64/kernel/head-xen.S
+++ b/arch/x86_64/kernel/head-xen.S
@@ -23,6 +23,7 @@
 #include <asm/msr.h>
 #include <asm/cache.h>
 #include <asm/dwarf2.h>
+#include <xen/interface/xen.h>
 #include <xen/interface/elfnote.h>
 #include <xen/interface/features.h>
 
@@ -80,6 +81,7 @@ NEXT_PAGE(level1_fixmap_pgt)
 
 NEXT_PAGE(hypercall_page)
 	CFI_STARTPROC
+	i = 0
 	.rept 0x1000 / 0x20
 	.skip 1 /* push %rcx */
 	CFI_ADJUST_CFA_OFFSET	8
@@ -87,15 +89,25 @@ NEXT_PAGE(hypercall_page)
 	.skip 2 /* push %r11 */
 	CFI_ADJUST_CFA_OFFSET	8
 	CFI_REL_OFFSET	r11,0
+	.if i == __HYPERVISOR_iret
+	.skip 1 /* push %rax */
+	CFI_ADJUST_CFA_OFFSET	8
+	CFI_REL_OFFSET	rax,0
+	.endif
 	.skip 5 /* mov $#,%eax */
 	.skip 2 /* syscall */
+	.if i == __HYPERVISOR_iret
+	CFI_ADJUST_CFA_OFFSET	-3*8
+	.else
 	.skip 2 /* pop %r11 */
 	CFI_ADJUST_CFA_OFFSET -8
 	CFI_RESTORE r11
 	.skip 1 /* pop %rcx */
 	CFI_ADJUST_CFA_OFFSET -8
 	CFI_RESTORE rcx
-	.align 0x20,0 /* ret */
+	.endif
+	.balign 0x20,0 /* ret */
+	i = i + 1
 	.endr
 	CFI_ENDPROC