linux-kernel - [PATCH] x86_32: Remove unnecessary use of %ebx as the boot cpu flag

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Date:	Mon, 21 Jan 2008 22:15:19 +0000
From:	Ian Campbell <ijc@...lion.org.uk>
To:	linux-kernel@...r.kernel.org
Cc:	Ian Campbell <ijc@...lion.org.uk>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Andi Kleen <andi@...stfloor.org>,
	Mika Penttilä <mika.penttila@...umbus.fi>
Subject: [PATCH] x86_32: Remove unnecessary use of %ebx as the boot cpu flag

Currently in head_32.S there are two ways we test to see if we
are the boot cpu.  By looking at %ebx and by looking at the
static variable ready.  When changing things around I have
found that it gets tricky to preserve %ebx.  So this
patch just switches head.S over to the more reliable
test of always using ready.

Hopefully later we can kill these tests entirely.

Signed-off-by: Eric W. Biederman <ebiederm@...ssion.com>
Signed-off-by: Ian Campbell <ijc@...lion.org.uk>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Andi Kleen <andi@...stfloor.org>
Cc: Mika Penttilä <mika.penttila@...umbus.fi>
---
 arch/x86/kernel/head_32.S |    7 +------
 1 files changed, 1 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
index f409fe2..7b9b256 100644
--- a/arch/x86/kernel/head_32.S
+++ b/arch/x86/kernel/head_32.S
@@ -199,7 +199,6 @@ default_entry:
 	addl $0x67, %eax			/* 0x67 == _PAGE_TABLE */
 	movl %eax, 4092(%edx)
 
-	xorl %ebx,%ebx				/* This is the boot CPU (BSP) */
 	jmp 3f
 /*
  * Non-boot CPU entry point; entered from trampoline.S
@@ -268,10 +267,6 @@ ENTRY(startup_32_smp)
 	wrmsr
 
 6:
-	/* This is a secondary processor (AP) */
-	xorl %ebx,%ebx
-	incl %ebx
-
 #endif /* CONFIG_SMP */
 3:
 
@@ -297,7 +292,7 @@ ENTRY(startup_32_smp)
 	popfl
 
 #ifdef CONFIG_SMP
-	andl %ebx,%ebx
+	cmpb $0, ready
 	jz  1f				/* Initial CPU cleans BSS */
 	jmp checkCPUtype
 1:
-- 
1.5.3.8

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