linux-kernel - [PATCH] x86/boot: reduce one instruction by adding delta to gdtr's base address

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Message-Id: <1478015364-5547-1-git-send-email-richard.weiyang@gmail.com>
Date:   Tue,  1 Nov 2016 15:49:24 +0000
From:   Wei Yang <richard.weiyang@...il.com>
To:     hpa@...or.com, tglx@...utronix.de, mingo@...hat.com
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Wei Yang <richard.weiyang@...il.com>
Subject: [PATCH] x86/boot: reduce one instruction by adding delta to gdtr's base address

%ebp contains the address where it is loaded and gdtr's base address is
already set to "gdt" in compilation. It is fine to get the correct base
address by adding the delta to gdtr's base address.

This patch fixes the gdtr's base address by adding delta to it and saves
one instruction.

Signed-off-by: Wei Yang <richard.weiyang@...il.com>
---
 arch/x86/boot/compressed/head_64.S | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index efdfba2..4d85e60 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -119,8 +119,7 @@ ENTRY(startup_32)
  */
 
 	/* Load new GDT with the 64bit segments using 32bit descriptor */
-	leal	gdt(%ebp), %eax
-	movl	%eax, gdt+2(%ebp)
+	addl	%ebp, gdt+2(%ebp)
 	lgdt	gdt(%ebp)
 
 	/* Enable PAE mode */
-- 
2.5.0