Re: asm (lidt) question

From: Randy.Dunlap (rddunlap@osdl.org)
Date: Tue Jul 22 2003 - 13:58:23 EST

On Tue, 22 Jul 2003 10:31:37 -0700 (PDT) Davide Libenzi <davidel@xmailserver.org> wrote:

| On Tue, 22 Jul 2003, Jamie Lokier wrote:
|
| > Davide Libenzi wrote:
| > > IMHO, since "var" is really an output parameter.
| >
| > "var" is read, not written.
| > I think you are confusing "lidt" with "sidt".
|
| Actually I don't even know what I was confusing, since L and S are not
| there for nothing ;) And yes, the form with =m as input parameter should
| be corrected, even if it generates the same code.

Yes, less confusion is better, so here's a patch to use the
same reasonable syntax in all places.

Look OK? Generates the same code, as Davide pointed out. 

--
~Randy

patch_name:	lidt_norm.patch
patch_version:	2003-07-22.11:47:21
author:		Randy.Dunlap <rddunlap@osdl.org>
description:	normalize lidt/lgdt syntax usage
product:	Linux
product_versions: 2.6.0-test1
diffstat:	=
 arch/i386/kernel/cpu/common.c |    4 ++--
 arch/i386/kernel/traps.c      |    2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff -Naur ./arch/i386/kernel/cpu/common.c~lidt ./arch/i386/kernel/cpu/common.c
--- ./arch/i386/kernel/cpu/common.c~lidt	2003-07-13 20:29:29.000000000 -0700
+++ ./arch/i386/kernel/cpu/common.c	2003-07-22 11:41:05.000000000 -0700
@@ -480,8 +480,8 @@
 	 */
 	memcpy(thread->tls_array, cpu_gdt_table[cpu], GDT_ENTRY_TLS_ENTRIES * 8);
 
-	__asm__ __volatile__("lgdt %0": "=m" (cpu_gdt_descr[cpu]));
-	__asm__ __volatile__("lidt %0": "=m" (idt_descr));
+	__asm__ __volatile__("lgdt %0": :"m" (cpu_gdt_descr[cpu]));
+	__asm__ __volatile__("lidt %0": :"m" (idt_descr));
 
 	/*
 	 * Delete NT
diff -Naur ./arch/i386/kernel/traps.c~lidt ./arch/i386/kernel/traps.c
--- ./arch/i386/kernel/traps.c~lidt	2003-07-13 20:31:20.000000000 -0700
+++ ./arch/i386/kernel/traps.c	2003-07-22 11:39:31.000000000 -0700
@@ -780,7 +780,7 @@
 	 * it uses the read-only mapped virtual address.
 	 */
 	idt_descr.address = fix_to_virt(FIX_F00F_IDT);
-	__asm__ __volatile__("lidt %0": "=m" (idt_descr));
+	__asm__ __volatile__("lidt %0": :"m" (idt_descr));
 }
 #endif
 

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