x86: Add multiboot header

By adding a multiboot header, U-Boot can be loaded by GRUB2. Using GRUB2 to
bootstrap U-Boot is useful for using an existing BIOS to get an initial
U-Boot port up and running before implementing the low-level reset vector
code, SDRAM init, etc. and overwriting the BIOS

Signed-off-by: Graeme Russ <graeme.russ@gmail.com>

diff --git a/arch/x86/cpu/start.S b/arch/x86/cpu/start.S
index 5adb387..d099fc9 100644 (file)
--- a/arch/x86/cpu/start.S
+++ b/arch/x86/cpu/start.S
@@ -129,3 +129,23 @@ die:       hlt
 blank_idt_ptr:
        .word   0               /* limit */
        .long   0               /* base */
+
+       .p2align        2       /* force 4-byte alignment */
+
+multiboot_header:
+       /* magic */
+       .long   0x1BADB002
+       /* flags */
+       .long   (1 << 16)
+       /* checksum */
+       .long   -0x1BADB002 - (1 << 16)
+       /* header addr */
+       .long   multiboot_header - _x86boot_start + CONFIG_SYS_TEXT_BASE
+       /* load addr */
+       .long   CONFIG_SYS_TEXT_BASE
+       /* load end addr */
+       .long   0
+       /* bss end addr */
+       .long   0
+       /* entry addr */
+       .long   CONFIG_SYS_TEXT_BASE