[PATCH 18/21] i386 Ldt cleanups 2

[Zachary Amsden <zach@vmware.com>]

Add an acessor function to get a pointer to an LDT descriptor.  Add one for
the GDT too, while we are here, and a function to tell the difference.

Turns out on some GCC versions, converting to char * and back gives better
code output than gdt[seg >> 3].  Lets keep that trick in the header file
so the C-code can be clean.

Not used yet, but soon.

Signed-off-by: Zachary Amsden <zach@vmware.com>
Index: linux-2.6.14-zach-work/include/asm-i386/desc.h
===================================================================
--- linux-2.6.14-zach-work.orig/include/asm-i386/desc.h	2005-11-04 18:10:53.000000000 -0800
+++ linux-2.6.14-zach-work/include/asm-i386/desc.h	2005-11-05 00:28:03.000000000 -0800
@@ -30,7 +30,24 @@ static inline struct desc_struct *get_cp
 {
 	return ((struct desc_struct *)cpu_gdt_descr[cpu].address);
 }
-  
+
+static inline int segment_from_ldt(unsigned int segment)
+{
+	return segment & LDT_SEGMENT;
+}
+
+static inline struct desc_struct *get_gdt_desc(int cpu, unsigned int segment)
+{
+	char *gdt = (char *)get_cpu_gdt_table(cpu);
+	return (struct desc_struct *)&gdt[segment & ~7];
+}
+
+static inline struct desc_struct *get_ldt_desc(mm_context_t *ctx, unsigned int segment)
+{
+	char *ldt = (char *)ctx->ldt;
+	return (struct desc_struct *)&ldt[segment & ~7];
+}
+
 #define load_TR_desc() __asm__ __volatile__("ltr %w0"::"q" (GDT_ENTRY_TSS*8))
 #define load_LDT_desc() __asm__ __volatile__("lldt %w0"::"q" (GDT_ENTRY_LDT*8))