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Subject[tip: x86/asm] x86/asm/suspend: Get rid of bogus_64_magic
The following commit has been merged into the x86/asm branch of tip:

Commit-ID: 559ceeed62a5121783a8955c63aeb18aaa0ef224
Gitweb: https://git.kernel.org/tip/559ceeed62a5121783a8955c63aeb18aaa0ef224
Author: Jiri Slaby <jslaby@suse.cz>
AuthorDate: Fri, 06 Sep 2019 09:55:49 +02:00
Committer: Borislav Petkov <bp@suse.de>
CommitterDate: Fri, 06 Sep 2019 10:34:15 +02:00

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
---
arch/x86/kernel/acpi/wakeup_64.S | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/acpi/wakeup_64.S b/arch/x86/kernel/acpi/wakeup_64.S
index b0715c3..7f9ade1 100644
--- 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
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