[patch V4 part 1 09/36] x86/entry/64: Avoid pointless code when CONTEXT_TRACKING=n

From: Thomas Gleixner
Date: Tue May 05 2020 - 10:23:48 EST


From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

GAS cannot optimize out the test and conditional jump when context tracking
is disabled and CALL_enter_from_user_mode is an empty macro.

Wrap it in #ifdeffery. Will go away once all this is moved to C.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Reviewed-by: Alexandre Chartre <alexandre.chartre@xxxxxxxxxx>
Acked-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
Acked-by: Andy Lutomirski <luto@xxxxxxxxxx>

---
arch/x86/entry/entry_64.S | 2 ++
1 file changed, 2 insertions(+)

--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -888,12 +888,14 @@ apicinterrupt IRQ_WORK_VECTOR irq_work
TRACE_IRQS_OFF
.endif

+#ifdef CONFIG_CONTEXT_TRACKING
.if \paranoid == 0
testb $3, CS(%rsp)
jz .Lfrom_kernel_no_context_tracking_\@
CALL_enter_from_user_mode
.Lfrom_kernel_no_context_tracking_\@:
.endif
+#endif

movq %rsp, %rdi /* pt_regs pointer */