The following commit has been merged into the x86/entry branch of tip:

Commit-ID:     cd19bff6935f29ad06513562b59ebdfe2d34eae4
Gitweb:        
https://git.kernel.org/tip/cd19bff6935f29ad06513562b59ebdfe2d34eae4
Author:        Thomas Gleixner <[email protected]>
AuthorDate:    Tue, 25 Feb 2020 23:16:08 +01:00
Committer:     Thomas Gleixner <[email protected]>
CommitterDate: Fri, 15 May 2020 20:03:04 +02:00

x86/entry/64: Avoid pointless code when CONTEXT_TRACKING=n

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 <[email protected]>
Reviewed-by: Alexandre Chartre <[email protected]>
Acked-by: Frederic Weisbecker <[email protected]>
Acked-by: Andy Lutomirski <[email protected]>
Acked-by: Peter Zijlstra <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]


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

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 7d40d10..f84b0f6 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -889,12 +889,14 @@ apicinterrupt IRQ_WORK_VECTOR                     
irq_work_interrupt              smp_irq_work_interrupt
        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 */
 

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