[PATCH 1/3] x86/kexec: Drop compatibility_mode_far

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

ljmp is (famously?) incompatible between Intel and AMD CPUs, and while we're
using one of the compatible forms, we've got a good stack and lret is the far
more common way of doing this.

No functional change.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
---
 xen/arch/x86/x86_64/kexec_reloc.S | 16 ++++------------
 1 file changed, 4 insertions(+), 12 deletions(-)

diff --git a/xen/arch/x86/x86_64/kexec_reloc.S 
b/xen/arch/x86/x86_64/kexec_reloc.S
index f4842025eb56..035164e96f38 100644
--- a/xen/arch/x86/x86_64/kexec_reloc.S
+++ b/xen/arch/x86/x86_64/kexec_reloc.S
@@ -86,12 +86,11 @@ ENTRY(kexec_reloc)
         movq    %rax, (compat_mode_gdt_desc + 2)(%rip)
         lgdt    compat_mode_gdt_desc(%rip)
 
-        /* Relocate compatibility mode entry point address. */
-        leal    compatibility_mode(%rip), %eax
-        movl    %eax, compatibility_mode_far(%rip)
-
         /* Enter compatibility mode. */
-        ljmp    *compatibility_mode_far(%rip)
+        lea     compatibility_mode(%rip), %rax
+        push    $0x10
+        push    %rax
+        lretq
 
 relocate_pages:
         /* %rdi - indirection page maddr */
@@ -171,13 +170,6 @@ compatibility_mode:
         ud2
 
         .align 4
-compatibility_mode_far:
-        .long 0x00000000             /* set in call_32_bit above */
-        .word 0x0010
-
-        .type compatibility_mode_far, @object
-        .size compatibility_mode_far, . - compatibility_mode_far
-
 compat_mode_gdt_desc:
         .word .Lcompat_mode_gdt_end - compat_mode_gdt -1
         .quad 0x0000000000000000     /* set in call_32_bit above */
-- 
2.30.2