linux-kernel - [PATCH 1/2] x86/boot/64: use 'push' instead of 'call' in start

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Date:   Tue, 13 Dec 2016 21:25:35 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>
Subject: [PATCH 1/2] 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@...en8.de>
Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
---
 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
-- 
2.7.4