Date: Thu, 3 Nov 2005 16:12:51 +0000 (GMT)
From: "Maciej W. Rozycki" <macro@linux-mips.org>
To: Zachary Amsden <zach@vmware.com>, linux-kernel@vger.kernel.org
Subject: 2.6.14: CR4 not needed to be inspected on the 486 anymore?
Message-ID: <Pine.LNX.4.55.0511031600010.24109@blysk.ds.pg.gda.pl>
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Hello,

 The following hunk of the 2.6.14 patch:

diff --git a/arch/i386/kernel/process.c b/arch/i386/kernel/process.c
index e3f362e..7a14fdf 100644
--- a/arch/i386/kernel/process.c
+++ b/arch/i386/kernel/process.c
@@ -313,16 +311,12 @@ void show_regs(struct pt_regs * regs)
 	printk(" DS: %04x ES: %04x\n",
 		0xffff & regs->xds,0xffff & regs->xes);
 
-	__asm__("movl %%cr0, %0": "=r" (cr0));
-	__asm__("movl %%cr2, %0": "=r" (cr2));
-	__asm__("movl %%cr3, %0": "=r" (cr3));
-	/* This could fault if %cr4 does not exist */
-	__asm__("1: movl %%cr4, %0		\n"
-		"2:				\n"
-		".section __ex_table,\"a\"	\n"
-		".long 1b,2b			\n"
-		".previous			\n"
-		: "=r" (cr4): "0" (0));
+	cr0 = read_cr0();
+	cr2 = read_cr2();
+	cr3 = read_cr3();
+	if (current_cpu_data.x86 > 4) {
+		cr4 = read_cr4();
+	}
 	printk("CR0: %08lx CR2: %08lx CR3: %08lx CR4: %08lx\n", cr0, cr2, cr3, cr4);
 	show_trace(NULL, &regs->esp);
 }

disables code to retrieve the actual value of CR4 on 486-class systems
(which may or may not implement the register, depending on the exact CPU
type and stepping).  This seems suspicious to me, but I have to admit I
haven't followed the discussion on the issue if there was any.

 Zachary, I think the change originates from you -- have you done it
deliberately (why?) or has it just been a mistake?

  Maciej
-
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