kernel: align gdt and idt base addresses

patch my fdmanana:
As recommended by the Intel 64 and IA-32 Architectures Developer's
Manual Volume 3A, the GDT and IDT base addresses should be aligned on an
8 byte boundary to yield better processor performance.

diff --git a/kernel/arch/i386/protect.c b/kernel/arch/i386/protect.c
index c6056a9ce043ed88d840d9373b147e617eff3112..4c5949d0ac66164f54b5db5603c6e1075f8077fa 100644 (file)
--- a/kernel/arch/i386/protect.c
+++ b/kernel/arch/i386/protect.c
@@ -25,7 +25,9 @@ struct gatedesc_s {
   u16_t offset_high;
 };
 
-struct segdesc_s gdt[GDT_SIZE]=                /* used in klib.s and mpx.s */
+
+/* used in klib.s and mpx.s */
+struct segdesc_s gdt[GDT_SIZE] __aligned(DESC_SIZE) =
 {      {0},
        {0,0,0,0},                              /* GDT descriptor */
        {0,0,0,0},                              /* IDT descriptor */
@@ -35,7 +37,9 @@ struct segdesc_s gdt[GDT_SIZE]=               /* used in klib.s and mpx.s */
        {0xffff,0,0,0x9b,0xcf,0},       /* kernel CS */
        {0xffff,0,0,0x9b,0xcf,0},       /* temp for BIOS (386: monitor CS at startup) */
 };
-static struct gatedesc_s idt[IDT_SIZE];        /* zero-init so none present */
+
+/* zero-init so none present */
+static struct gatedesc_s idt[IDT_SIZE] __aligned(DESC_SIZE);
 struct tss_s tss[CONFIG_MAX_CPUS];                     /* zero init */
 
 static void sdesc(struct segdesc_s *segdp, phys_bytes base, vir_bytes