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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 <tglx@linutronix.de>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Acked-by: Frederic Weisbecker <frederic@kernel.org>
Acked-by: Andy Lutomirski <luto@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200505134058.955968069@linutronix.de
This commit is contained in:
Thomas Gleixner 2020-02-25 23:16:08 +01:00
parent e9660391d0
commit 725005897e
1 changed files with 2 additions and 0 deletions
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arch/x86/entry/entry_64.S
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@ -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 */