* bootstub version 0.01

1 files changed, 58 insertions, 0 deletions

diff --git a/head.S b/head.S
new file mode 100644
index 0000000..7431584
--- /dev/null
+++ b/head.S
@@ -0,0 +1,58 @@
+/* head.S for bootstub to load protected mode kernel
+ * Copyright (C) 2008 Alek Du <alek.du@intel.com>
+ * 
+ * Note. When FW hand-off control to bootstub, the CPU is already in protected
+ * Mode with 1. GDT(8)=4G GDT(10)=4G
+ *           2. CS=8, DS=ES=FS=GS=10
+ *           3. Paging mode disabled
+ *           4. Interrupt ENABLED
+ */ 
+
+/* When bootstub get control, the memory map in DRAM is like:
+ *		~			~
+ * 0x102000	|	initramfs	|
+ *+bzImage size +-----------------------+
+ *		|	bzImage		|
+ * 0x102000	+-----------------------+
+ *		|	boot stub	|
+ * 0x101000	+-----------------------+
+ *		|	free space	|
+ *		|	used as stack   |
+ * 0x100100	+-----------------------+
+ *		|	kernel cmdline	|
+ * 0x100000	+-----------------------+
+*/
+
+#include "bootstub.h"
+
+.text
+
+.section ".text.head","ax",@progbits
+	.globl _start
+
+_start:
+	cld
+	cli
+	/* DS=ES=FS=GS=10 */
+	movl 0x2, %eax	
+	movl %eax, %ds
+	movl %eax, %es
+	movl %eax, %fs
+	movl %eax, %gs
+	movl %eax, %ss
+	/* setup stack, because we are heading off to "C" */
+	movl $STACK_OFFSET, %esp
+	/* after call main, GDT was set (0x10 and 0x18) IDT was clear
+	 * eax will store 32bit entry of bzImage
+         */
+	calll main
+	ljmp $__BOOT_CS,$1f
+1:	
+	/* tell kernel where is boot_param */
+	movl $(BOOT_PARAMS_OFFSET), %esi
+	xor %ebp, %ebp
+	xor %edi, %edi
+	xor %ebx, %ebx
+	
+	jmpl *%eax    # Jump to the 32-bit entrypoint
+