*/
#include "threads/loader.h"
-#include "threads/mmu.h"
+
+ .intel_syntax noprefix
#### Kernel loader.
#### memory, and jumps to the first byte of the kernel, where start.S
#### is linked.
-/* Flags in control register 0 */
+/* Flags in control register 0. */
#define CR0_PE 0x00000001 /* Protection Enable. */
#define CR0_EM 0x00000004 /* (Floating-point) Emulation. */
#define CR0_PG 0x80000000 /* Paging. */
# Code runs in real mode, which is a 16-bit segment.
+.globl start
+start:
.code16
# Disable interrupts.
cli
cld
-# Set up data segments and stack.
+# Set up data segments.
- subw %ax, %ax
- movw %ax, %es
- movw %ax, %ds
+ sub ax, ax
+ mov es, ax
+ mov ds, ax
+# Set up stack segment.
# Stack grows downward starting from us.
# We don't ever use the stack so this is strictly speaking
# unnecessary.
- movw %ax, %ss
- movw $0x7c00, %sp
+ mov ss, ax
+ mov sp, 0x7c00
#### Enable A20. Address line 20 is tied to low when the machine
#### boots, which prevents addressing memory about 1 MB. This code
# Poll status register while busy.
-1: inb $0x64, %al
- testb $0x2, %al
+1: in al, 0x64
+ test al, 0x2
jnz 1b
# Send command for writing output port.
- movb $0xd1, %al
- outb %al, $0x64
+ mov al, 0xd1
+ outb 0x64, al
# Poll status register while busy.
-1: inb $0x64, %al
- testb $0x2, %al
+1: in al, 0x64
+ test al, 0x2
jnz 1b
# Enable A20 line.
- movb $0xdf, %al
- outb %al, $0x60
+ mov al, 0xdf
+ out 0x60, al
-#### Get memory size, via interrupt 15h function 88h. Returns CF
+#### Get memory size, via interrupt 15h function 88h, which returns CF
#### clear if successful, with AX = (kB of physical memory) - 1024.
#### This only works for memory sizes <= 65 MB, which should be fine
-#### for our purposes.
+#### for our purposes. We cap memory at 64 MB because that's all we
+#### prepare page tables for, below.
- movb $0x88, %ah
- int $0x15
- jc panic # Carry flag set on error
- addl $1024, %eax # Total kB
- shrl $2, %eax # Total 4 kB pages
- movl %eax, ram_pages
+ mov ah, 0x88
+ int 0x15
+ jc panic
+ cli # BIOS might have enabled interrupts
+ add eax, 1024 # Total kB memory
+ cmp eax, 0x10000 # Cap at 64 MB
+ jbe 1f
+ mov eax, 0x10000
+1: shr eax, 2 # Total 4 kB pages
+ mov ram_pgs, eax
#### Create temporary page directory and page table and set page
#### directory base register.
# Create page directory at 64 kB and fill with zeroes.
+ mov ax, 0x1000
+ mov es, ax
+ sub eax, eax
+ sub edi, edi
+ mov ecx, 0x400
+ rep stosd
+
+# Add PDEs to point to PTEs for the first 64 MB of RAM.
+# Also add identical PDEs starting at LOADER_PHYS_BASE.
+# See [IA32-v3] section 3.7.6 for a description of the bits in eax.
+
+# A bug in some versions of GAS prevents us from using the straightforward
+# mov es:[di + LOADER_PHYS_BASE / 1024 / 1024], eax
+# so we calculate the displacement in bx instead.
+
+ mov eax, 0x11007
+ mov ecx, 0x11
+ sub di, di
+ mov ebx, LOADER_PHYS_BASE
+ shr ebx, 20
+1: mov es:[di], eax
+ mov es:[bx + di], eax
+ add di, 4
+ add eax, 0x1000
+ loop 1b
- mov $0x1000, %ax
- mov %ax, %es
- subl %eax, %eax
- subl %edi, %edi
- movl $0x400, %ecx
- rep stosl
-
-# Set PDEs for 0 and LOADER_PHYS_BASE to point to the page table.
-
- movl $0x11000 | PG_U | PG_W | PG_P, %eax
- movl %eax, %es:0
- movl %eax, %es:LOADER_PHYS_BASE >> 20
-
-# Initialize page table.
-
- movl $PG_U | PG_W | PG_P, %eax
- movl $0x400, %ecx
-1: stosl
- addl $0x1000, %eax
+# Set up one-to-map linear to physical map for the first 64 MB of RAM.
+# See [IA32-v3] section 3.7.6 for a description of the bits in eax.
+
+ mov ax, 0x1100
+ mov es, ax
+ mov eax, 0x7
+ mov cx, 0x4000
+ sub di, di
+1: mov es:[di], eax
+ add di, 4
+ add eax, 0x1000
loop 1b
# Set page directory base register.
- movl $0x10000, %eax
- movl %eax, %cr3
+ mov eax, 0x10000
+ mov cr3, eax
#### Switch to protected mode.
-# First we turn off interrupts because we don't set up an IDT.
-
- cli
-
# Then we point the GDTR to our GDT. Protected mode requires a GDT.
# We need a data32 prefix to ensure that all 32 bits of the GDT
# descriptor are loaded (default is to load only 24 bits).
# EM (Emulation): forces floating-point instructions to trap.
# We don't support floating point.
- movl %cr0, %eax
- orl $CR0_PE | CR0_PG | CR0_WP | CR0_EM, %eax
- movl %eax, %cr0
+ mov eax, cr0
+ or eax, CR0_PE + CR0_PG + CR0_WP + CR0_EM
+ mov cr0, eax
# We're now in protected mode in a 16-bit segment. The CPU still has
-# the real-mode code segment cached in %cs's segment descriptor. We
-# need to reload %cs, and the easiest way is to use a far jump.
+# the real-mode code segment cached in cs's segment descriptor. We
+# need to reload cs, and the easiest way is to use a far jump.
# Because we're not in a 32-bit segment the data32 prefix is needed to
# jump to a 32-bit offset.
- data32 ljmp $SEL_KCSEG, $1f + LOADER_PHYS_BASE
-
+ data32 ljmp SEL_KCSEG, 1f + LOADER_PHYS_BASE
+
# We're now in protected mode in a 32-bit segment.
.code32
# Reload all the other segment registers and the stack pointer to
# point into our new GDT.
-1: movw $SEL_KDSEG, %ax
- movw %ax, %ds
- movw %ax, %es
- movw %ax, %fs
- movw %ax, %gs
- movw %ax, %ss
- movl $LOADER_PHYS_BASE + 0x20000, %esp
+1: mov ax, SEL_KDSEG
+ mov ds, ax
+ mov es, ax
+ mov fs, ax
+ mov gs, ax
+ mov ss, ax
+ mov esp, LOADER_PHYS_BASE + 0x30000
#### Load kernel starting at physical address LOADER_KERN_BASE by
#### frobbing the IDE controller directly.
- movl $1, %ebx
- movl $LOADER_KERN_BASE + LOADER_PHYS_BASE, %edi
+ mov ebx, 1
+ mov edi, LOADER_KERN_BASE + LOADER_PHYS_BASE
read_sector:
# Poll status register while controller busy.
- movl $0x1f7, %edx
-1: inb %dx, %al
- testb $0x80, %al
+ mov edx, 0x1f7
+1: in al, dx
+ test al, 0x80
jnz 1b
# Read a single sector.
- movl $0x1f2, %edx
- movb $1, %al
- outb %al, %dx
+ mov edx, 0x1f2
+ mov al, 1
+ out dx, al
# Sector number to write in low 28 bits.
# LBA mode, device 0 in top 4 bits.
- movl %ebx, %eax
- andl $0x0fffffff, %eax
- orl $0xe0000000, %eax
+ mov eax, ebx
+ and eax, 0x0fffffff
+ or eax, 0xe0000000
-# Dump %eax to ports 0x1f3...0x1f6.
+# Dump eax to ports 0x1f3...0x1f6.
- movl $4, %ecx
-1: incw %dx
- outb %al, %dx
- shrl $8, %eax
+ mov ecx, 4
+1: inc dx
+ out dx, al
+ shr eax, 8
loop 1b
# READ command to command register.
- incw %dx
- movb $0x20, %al
- outb %al, %dx
+ inc dx
+ mov al, 0x20
+ out dx, al
# Poll status register while controller busy.
-1: inb %dx, %al
- testb $0x80, %al
+1: in al, dx
+ test al, 0x80
jnz 1b
# Poll status register until data ready.
-1: inb %dx, %al
- testb $0x08, %al
+1: in al, dx
+ test al, 0x08
jz 1b
# Transfer sector.
- movl $512 / 4, %ecx
- movl $0x1f0, %edx
- rep insl
+ mov ecx, 256
+ mov edx, 0x1f0
+ rep insw
# Next sector.
- incl %ebx
- cmpl $KERNEL_LOAD_PAGES*8 + 1, %ebx
+ inc ebx
+ cmp ebx, KERNEL_LOAD_PAGES*8 + 1
jnz read_sector
#### Jump to kernel entry point.
- movl $LOADER_PHYS_BASE + LOADER_KERN_BASE, %eax
- call *%eax
+ mov eax, LOADER_PHYS_BASE + LOADER_KERN_BASE
+ call eax
jmp panic
#### GDT
#### Print panicmsg (with help from the BIOS) and spin.
panic: .code16 # We only panic in real mode.
- movw $panicmsg, %si
- movb $0xe, %ah
- subb %bh, %bh
+ mov si, offset panic_message
+ mov ah, 0xe
+ sub bh, bh
1: lodsb
- test %al, %al
+ test al, al
2: jz 2b # Spin.
- int $0x10
+ int 0x10
jmp 1b
-panicmsg:
- .ascii "Loader panic!\r\n"
+panic_message:
+ .ascii "Panic!"
.byte 0
-#### Memory size in 4 kB pages.
- .org LOADER_RAM_PAGES - LOADER_BASE
-ram_pages:
+#### Physical memory size in 4 kB pages.
+#### This is initialized by the loader and read by the kernel.
+ .org LOADER_RAM_PGS - LOADER_BASE
+ram_pgs:
.long 0
-#### Command-line arguments inserted by another utility.
-#### The loader doesn't use these, but we note their
-#### location here for easy reference.
- .org LOADER_CMD_LINE - LOADER_BASE
-cmd_line:
+#### Command-line arguments and their count.
+#### This is written by the `pintos' utility and read by the kernel.
+#### The loader itself does not do anything with the command line.
+ .org LOADER_ARG_CNT - LOADER_BASE
+arg_cnt:
+ .long 0
+ .org LOADER_ARGS - LOADER_BASE
+args:
.fill 0x80, 1, 0
-#### Boot-sector signature for BIOS inspection.
- .org LOADER_BIOS_SIG - LOADER_BASE
+#### Boot-sector signature.
+#### The BIOS checks that this is set properly.
+ .org LOADER_SIG - LOADER_BASE
.word 0xaa55
projects / pintos-anon / blobdiff