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

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

[Wei Yang]

%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@gmail.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

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

[tip-bot for Wei Yang]

Commit-ID:  064025f7ea1ebcd9bbb99cfa9492a803e8b01d36
Gitweb:     http://git.kernel.org/tip/064025f7ea1ebcd9bbb99cfa9492a803e8b01d36
Author:     Wei Yang <richard.weiyang@gmail.com>
AuthorDate: Tue, 1 Nov 2016 15:49:24 +0000
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 7 Nov 2016 08:33:59 +0100

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>
---
 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 */