From: Wei Yang <richard.weiyang@gmail.com>
Date: Tue, 1 Nov 2016 15:49:24 +0000 (+0000)
Subject: x86/boot: Simplify the GDTR calculation assembly code a bit
X-Git-Url: http://git.lede-project.org./?a=commitdiff_plain;h=064025f7ea1ebcd9bbb99cfa9492a803e8b01d36;p=openwrt%2Fstaging%2Fblogic.git

x86/boot: Simplify the GDTR calculation assembly code a bit

This patch calculates the GDTR's base address via a single instruction.

( 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. )

Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1478015364-5547-1-git-send-email-richard.weiyang@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index efdfba21a5b2..4d85e600db78 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 */