From 89bfdd4db183cbe75a3a0c2254ca48a50e37276f Mon Sep 17 00:00:00 2001
From: Russ Cox <rsc@swtch.com>
Date: Tue, 11 Jan 2011 13:27:45 -0500
Subject: [PATCH] multiboot support and memory-only (no disk) kernel
---
Makefile | 24 +++++++++++++++--
multiboot.S | 75 +++++++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 97 insertions(+), 2 deletions(-)
create mode 100644 multiboot.S
diff --git a/Makefile b/Makefile
index 95247ff..980543a 100644
--- a/Makefile
+++ b/Makefile
@@ -82,6 +82,11 @@ xv6.img: bootblock kernel fs.img
dd if=bootblock of=xv6.img conv=notrunc
dd if=kernel of=xv6.img seek=1 conv=notrunc
+xv6memfs.img: bootblock kernelmemfs
+ dd if=/dev/zero of=xv6memfs.img count=10000
+ dd if=bootblock of=xv6memfs.img conv=notrunc
+ dd if=kernelmemfs of=xv6memfs.img seek=1 conv=notrunc
+
bootblock: bootasm.S bootmain.c
$(CC) $(CFLAGS) -fno-pic -O -nostdinc -I. -c bootmain.c
$(CC) $(CFLAGS) -fno-pic -nostdinc -I. -c bootasm.S
@@ -102,11 +107,23 @@ initcode: initcode.S
$(OBJCOPY) -S -O binary initcode.out initcode
$(OBJDUMP) -S initcode.o > initcode.asm
-kernel: $(OBJS) bootother initcode
- $(LD) $(LDFLAGS) -Ttext 0x100000 -e main -o kernel $(OBJS) -b binary initcode bootother
+kernel: $(OBJS) multiboot.o bootother initcode
+ $(LD) $(LDFLAGS) -Ttext 0x100000 -e main -o kernel multiboot.o $(OBJS) -b binary initcode bootother fs.img
$(OBJDUMP) -S kernel > kernel.asm
$(OBJDUMP) -t kernel | sed '1,/SYMBOL TABLE/d; s/ .* / /; /^$$/d' > kernel.sym
+# kernelmemfs is a copy of kernel that maintains the
+# disk image in memory instead of writing to a disk.
+# This is not so useful for testing persistent storage or
+# exploring disk buffering implementations, but it is
+# great for testing the kernel on real hardware without
+# needing a scratch disk.
+MEMFSOBJS = $(filter-out ide.o,$(OBJS)) memide.o
+kernelmemfs: $(MEMFSOBJS) multiboot.o bootother initcode fs.img
+ $(LD) $(LDFLAGS) -Ttext 0x100000 -e main -o kernelmemfs multiboot.o $(MEMFSOBJS) -b binary initcode bootother fs.img
+ $(OBJDUMP) -S kernelmemfs > kernelmemfs.asm
+ $(OBJDUMP) -t kernelmemfs | sed '1,/SYMBOL TABLE/d; s/ .* / /; /^$$/d' > kernelmemfs.sym
+
tags: $(OBJS) bootother.S _init
etags *.S *.c
@@ -187,6 +204,9 @@ QEMUOPTS = -hdb fs.img xv6.img -smp $(CPUS)
qemu: fs.img xv6.img
$(QEMU) -serial mon:stdio $(QEMUOPTS)
+qemu-memfs: xv6memfs.img
+ $(QEMU) xv6memfs.img -smp $(CPUS)
+
qemu-nox: fs.img xv6.img
$(QEMU) -nographic $(QEMUOPTS)
diff --git a/multiboot.S b/multiboot.S
new file mode 100644
index 0000000..2579b6d
--- /dev/null
+++ b/multiboot.S
@@ -0,0 +1,75 @@
+# Multiboot header, for multiboot boot loaders like GNU Grub.
+# http://www.gnu.org/software/grub/manual/multiboot/multiboot.html
+#
+# Using GRUB 2, you can boot xv6 from a file stored in a
+# Linux file system by copying kernel or kernelmemfs to /boot
+# and then adding this menu entry:
+#
+# menuentry "xv6" {
+# insmod ext2
+# set root='(hd0,msdos1)'
+# set kernel='/boot/kernel'
+# echo "Loading ${kernel}..."
+# multiboot ${kernel} ${kernel}
+# boot
+# }
+
+#include "asm.h"
+
+#define STACK 4096
+
+#define SEG_KCODE 1 // kernel code
+#define SEG_KDATA 2 // kernel data+stack
+
+# Multiboot header. Data to direct multiboot loader.
+.p2align 2
+.text
+.globl multiboot_header
+multiboot_header:
+ #define magic 0x1badb002
+ #define flags (1<<16 | 1<<0)
+ .long magic
+ .long flags
+ .long (-magic-flags)
+ .long multiboot_header # beginning of image
+ .long multiboot_header
+ .long edata
+ .long end
+ .long multiboot_entry
+
+# Multiboot entry point. Machine is mostly set up.
+# Configure the GDT to match the environment that our usual
+# boot loader - bootasm.S - sets up.
+.globl multiboot_entry
+multiboot_entry:
+ lgdt gdtdesc
+ ljmp $(SEG_KCODE<<3), $mbstart32
+
+mbstart32:
+ # Set up the protected-mode data segment registers
+ movw $(SEG_KDATA<<3), %ax # Our data segment selector
+ movw %ax, %ds # -> DS: Data Segment
+ movw %ax, %es # -> ES: Extra Segment
+ movw %ax, %ss # -> SS: Stack Segment
+ movw $0, %ax # Zero segments not ready for use
+ movw %ax, %fs # -> FS
+ movw %ax, %gs # -> GS
+
+ # Set up the stack pointer and call into C.
+ movl $(stack + STACK), %esp
+ call main
+spin:
+ jmp spin
+
+# Bootstrap GDT
+.p2align 2 # force 4 byte alignment
+gdt:
+ SEG_NULLASM # null seg
+ SEG_ASM(STA_X|STA_R, 0x0, 0xffffffff) # code seg
+ SEG_ASM(STA_W, 0x0, 0xffffffff) # data seg
+
+gdtdesc:
+ .word (gdtdesc - gdt - 1) # sizeof(gdt) - 1
+ .long gdt # address gdt
+
+.comm stack, STACK
--
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