[PATCH v8 06/12] x86-64, hotplug: Add start_cpu0() entry point to head_64.S

["Fenghua Yu" <fenghua.yu@intel.com>]

From: Fenghua Yu <fenghua.yu@intel.com>

start_cpu0() is defined in head_64.S for 64-bit. The function sets up stack and
jumps to start_secondary() for CPU0 wake up.

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
---
 arch/x86/kernel/head_64.S |   15 +++++++++++++++
 1 files changed, 15 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 94bf9cc..3faac8a 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -252,6 +252,21 @@ ENTRY(secondary_startup_64)
 	pushq	%rax		# target address in negative space
 	lretq
 
+#ifdef CONFIG_HOTPLUG_CPU
+/*
+ * Boot CPU0 entry point. It's called from play_dead(). Everything has been set
+ * up already except stack. We just set up stack here. Then call
+ * start_secondary().
+ */
+ENTRY(start_cpu0)
+	movq stack_start(%rip),%rsp
+	movq	initial_code(%rip),%rax
+	pushq	$0		# fake return address to stop unwinder
+	pushq	$__KERNEL_CS	# set correct cs
+	pushq	%rax		# target address in negative space
+	lretq
+#endif
+
 	/* SMP bootup changes these two */
 	__REFDATA
 	.align	8
-- 
1.7.2