[Xen-devel] [PATCH] linux-2.6.18/x86-64: fix HYPERVISOR_iret unwind annotation

["Jan Beulich" <JBeulich@xxxxxxxx>]

Minimally for %rax this needs to reflect that the value is no longer
saved: Since the whole hypercall page is covered by a single FDE,
subsequent entries would otherwise retain the state of %rax being saved
on the stack, yet the offset it's being saved at is out of bounds for
the "normal" hypercall stubs.

Breaking up the single FDE into per stub ones would increase the size
of the resulting .eh_frame section, which is already quite big for this
simple a piece of code.

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

--- a/arch/x86_64/kernel/head-xen.S
+++ b/arch/x86_64/kernel/head-xen.S
@@ -98,6 +98,9 @@ NEXT_PAGE(hypercall_page)
        .skip 2 /* syscall */
        .if i == __HYPERVISOR_iret
        CFI_ADJUST_CFA_OFFSET   -3*8
+       CFI_SAME_VALUE  rax
+       CFI_SAME_VALUE  r11
+       CFI_SAME_VALUE  rcx
        .else
        .skip 2 /* pop %r11 */
        CFI_ADJUST_CFA_OFFSET -8
--- a/include/asm-x86_64/dwarf2.h
+++ b/include/asm-x86_64/dwarf2.h
@@ -28,6 +28,7 @@
 #define CFI_REMEMBER_STATE .cfi_remember_state
 #define CFI_RESTORE_STATE .cfi_restore_state
 #define CFI_UNDEFINED .cfi_undefined
+#define CFI_SAME_VALUE .cfi_same_value
 
 #else
 
@@ -45,6 +46,7 @@
 #define CFI_REMEMBER_STATE     #
 #define CFI_RESTORE_STATE      #
 #define CFI_UNDEFINED  #
+#define CFI_SAME_VALUE         #
 
 #endif

Attachment: xen-x86_64-hypercall-iret-unwind.patch
Description: Text document

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