linux-kernel - [PATCH] x86/head_64.S: do not use temporary register to check alignment

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Date:	Sat, 23 Jan 2016 12:50:28 +0600
From:	Alexander Kuleshov <kuleshovmail@...il.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Ingo Molnar <mingo@...hat.com>, "H . Peter Anvin" <hpa@...or.com>,
	Andy Lutomirski <luto@...nel.org>,
	Borislav Petkov <bp@...e.de>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	Alexander Kuleshov <kuleshovmail@...il.com>
Subject: [PATCH] x86/head_64.S: do not use temporary register to check alignment

We are using temporary %rax register during checking of kernel address
alignment. We can ged rid of it since testl instruction is safe and does
not change value of the rbp register.

Signed-off-by: Alexander Kuleshov <kuleshovmail@...il.com>
Suggested-by: Brian Gerst <brgerst@...il.com>
---
 arch/x86/kernel/head_64.S | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index ffdc0e8..7c21029 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -76,9 +76,7 @@ startup_64:
 	subq	$_text - __START_KERNEL_map, %rbp
 
 	/* Is the address not 2M aligned? */
-	movq	%rbp, %rax
-	andl	$~PMD_PAGE_MASK, %eax
-	testl	%eax, %eax
+	testl	$~PMD_PAGE_MASK, %ebp
 	jnz	bad_address
 
 	/*
-- 
2.7.0.25.gfc10eb5