x86/asm/suspend: Get rid of bogus_64_magic

bogus_64_magic is only a dead-end loop. There is no need for an
out-of-order function (and unannotated local label), so just handle it
in-place and also store 0xbad-m-a-g-i-c to %rcx beforehand, in case
someone is inspecting registers.

Here a qemu+gdb example:

  Remote debugging using localhost:1235
  wakeup_long64 () at arch/x86/kernel/acpi/wakeup_64.S:26
  26              jmp 1b
  (gdb) info registers
  rax            0x123456789abcdef0       1311768467463790320
  rbx            0x0      0
  rcx            0xbad6d61676963  3286910041024867
  		 ^^^^^^^^^^^^^^^

 [ bp: Add the gdb example. ]

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Len Brown <lenb@kernel.org>
Cc: linux-pm@vger.kernel.org
Cc: Pavel Machek <pavel@ucw.cz>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/20190906075550.23435-1-jslaby@suse.cz

diff --git a/arch/x86/kernel/acpi/wakeup_64.S b/arch/x86/kernel/acpi/wakeup_64.S
index b0715c3..7f9ade1 100644 (file)
--- a/arch/x86/kernel/acpi/wakeup_64.S
+++ b/arch/x86/kernel/acpi/wakeup_64.S
@@ -18,8 +18,13 @@ ENTRY(wakeup_long64)
        movq    saved_magic, %rax
        movq    $0x123456789abcdef0, %rdx
        cmpq    %rdx, %rax
-       jne     bogus_64_magic
+       je      2f
 
+       /* stop here on a saved_magic mismatch */
+       movq $0xbad6d61676963, %rcx
+1:
+       jmp 1b
+2:
        movw    $__KERNEL_DS, %ax
        movw    %ax, %ss        
        movw    %ax, %ds
@@ -37,9 +42,6 @@ ENTRY(wakeup_long64)
        jmp     *%rax
 ENDPROC(wakeup_long64)
 
-bogus_64_magic:
-       jmp     bogus_64_magic
-
 ENTRY(do_suspend_lowlevel)
        FRAME_BEGIN
        subq    $8, %rsp