Convert linux bootrom to external rom and fw_cfg

We already have a working multiboot implementation that uses fw_cfg to get
its kernel module etc. data in int19 runtime now.

So what's missing is a working linux boot option rom. While at it I figured it
would be a good idea to take the opcode generator out of pc.c and instead use
a proper option rom, like we do with multiboot.

So here it is - an fw_cfg using option rom for -kernel with linux!

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

pc-bios/optionrom/Makefile

@@ -13,7 +13,7 @@ CFLAGS += -I$(SRC_PATH)
 CFLAGS += $(call cc-option, $(CFLAGS), -fno-stack-protector)
 QEMU_CFLAGS = $(CFLAGS)
 
-build-all: multiboot.bin
+build-all: multiboot.bin linuxboot.bin
 
 %.img: %.o
 	$(call quiet-command,$(LD) -Ttext 0 -e _start -s -o $@ $<,"  Building $(TARGET_DIR)$@")

pc-bios/optionrom/linuxboot.S

@@ -0,0 +1,140 @@
+/*
+ * Linux Boot Option ROM
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ *
+ * Copyright Novell Inc, 2009
+ *   Authors: Alexander Graf <agraf@suse.de>
+ *
+ * Based on code in hw/pc.c.
+ */
+
+#include "optionrom.h"
+
+BOOT_ROM_START
+
+run_linuxboot:
+
+	cli
+	cld
+
+	jmp		copy_kernel
+boot_kernel:
+
+	read_fw		FW_CFG_SETUP_ADDR
+
+	mov		%eax, %ebx
+	shr		$4, %ebx
+
+	/* All segments contain real_addr */
+	mov		%bx, %ds
+	mov		%bx, %es
+	mov		%bx, %fs
+	mov		%bx, %gs
+	mov		%bx, %ss
+
+	/* CX = CS we want to jump to */
+	add		$0x20, %bx
+	mov		%bx, %cx
+
+	/* SP = cmdline_addr-real_addr-16 */
+	read_fw		FW_CFG_CMDLINE_ADDR
+	mov		%eax, %ebx
+	read_fw		FW_CFG_SETUP_ADDR
+	sub		%eax, %ebx
+	sub		$16, %ebx
+	mov		%ebx, %esp
+
+	/* Build indirect lret descriptor */
+	pushw		%cx		/* CS */
+	xor		%ax, %ax
+	pushw		%ax		/* IP = 0 */
+
+	/* Clear registers */
+	xor		%eax, %eax
+	xor		%ebx, %ebx
+	xor		%ecx, %ecx
+	xor		%edx, %edx
+	xor		%edi, %edi
+	xor		%ebp, %ebp
+
+	/* Jump to Linux */
+	lret
+
+
+copy_kernel:
+
+	/* We need to load the kernel into memory we can't access in 16 bit
+	   mode, so let's get into 32 bit mode, write the kernel and jump
+	   back again. */
+
+	/* Set DS to SS+SP - 0x10, so we can write our GDT descriptor there */
+	mov		%ss, %eax
+	shl		$4, %eax
+	add		%esp, %eax
+	sub		$0x10, %eax
+	shr		$4, %eax
+
+	/* Now create the GDT descriptor */
+	mov		%cs, %eax
+	shl		$4, %eax
+	movw		$((3 * 8) - 1), %bx
+	movw		%bx, %gs:0
+	movl		$gdt, %ebx
+	add		%eax, %ebx
+	movl		%ebx, %gs:2
+
+	/* And load the GDT */
+	data32 lgdt	%gs:0
+
+	/* Get us to protected mode now */
+	mov		$1, %eax
+	mov		%eax, %cr0
+
+	/* So we can set DS to a 32-bit segment */
+	mov		$0x10, %eax
+	mov		%eax, %ds
+
+	/* We're now running in 16-bit CS, but 32-bit DS! */
+
+	/* Load kernel and initrd */
+	read_fw_blob(FW_CFG_KERNEL)
+	read_fw_blob(FW_CFG_INITRD)
+	read_fw_blob(FW_CFG_CMDLINE)
+	read_fw_blob(FW_CFG_SETUP)
+
+	/* And now jump into Linux! */
+	mov		$0, %eax
+	mov		%eax, %cr0
+
+	/* DS = CS */
+	mov		%cs, %ax
+	mov		%ax, %ds
+
+	jmp		boot_kernel
+
+/* Variables */
+
+.align 4, 0
+gdt:
+	/* 0x00 */
+.byte	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
+
+	/* 0x08: code segment (base=0, limit=0xfffff, type=32bit code exec/read, DPL=0, 4k) */
+.byte	0xff, 0xff, 0x00, 0x00, 0x00, 0x9a, 0xcf, 0x00
+
+	/* 0x10: data segment (base=0, limit=0xfffff, type=32bit data read/write, DPL=0, 4k) */
+.byte	0xff, 0xff, 0x00, 0x00, 0x00, 0x92, 0xcf, 0x00
+
+BOOT_ROM_END