[tip:x86/urgent] x86/boot/64: Use 'push' instead of 'call' in start_cpu()

From: tip-bot for Josh Poimboeuf
Date: Wed Dec 14 2016 - 03:38:26 EST

Commit-ID: ec2d86a9b646d93f1948569f368e2c6f5449e6c7
Gitweb: http://git.kernel.org/tip/ec2d86a9b646d93f1948569f368e2c6f5449e6c7
Author: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
AuthorDate: Tue, 13 Dec 2016 21:25:35 -0600
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Wed, 14 Dec 2016 08:48:05 +0100

x86/boot/64: Use 'push' instead of 'call' in start_cpu()

start_cpu() pushes a text address on the stack so that stack traces from
idle tasks will show start_cpu() at the end. But it uses a call
instruction to do that, which is rather obtuse. Use a straightforward
push instead.

Suggested-by: Borislav Petkov <bp@xxxxxxxxx>
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/4d8a1952759721d42d1e62ba9e4a7e3ac5df8574.1481685203.git.jpoimboe@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
arch/x86/kernel/head_64.S | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 90de288..1facaf4 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -298,7 +298,7 @@ ENTRY(start_cpu)
* REX.W + FF /5 JMP m16:64 Jump far, absolute indirect,
* address given in m16:64.
- call 1f # put return address on stack for unwinder
+ pushq $1f # put return address on stack for unwinder
1: xorq %rbp, %rbp # clear frame pointer
movq initial_code(%rip), %rax
pushq $__KERNEL_CS # set correct cs