*/
#include "threads/loader.h"
-/*#include "threads/mmu.h"*/
#### 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. */
cli
cld
-# Set up data segments and stack.
+# Set up data segments.
subw %ax, %ax
movw %ax, %es
movw %ax, %ds
+# Set up stack segment.
# Stack grows downward starting from us.
-# We don't ever use the stack so this is strictly speaking
-# unnecessary.
+# We don't ever use the stack, but we call into the BIOS,
+# which might.
movw %ax, %ss
movw $0x7c00, %sp
#### Get memory size, via interrupt 15h function 88h. 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
+ jc panic
+ cli # BIOS might have enabled interrupts
+ addl $1024, %eax # Total kB memory
+ cmp $0x10000, %eax # Cap at 64 MB
+ jbe 1f
+ mov $0x10000, %eax
+1: shrl $2, %eax # Total 4 kB pages
+ movl %eax, ram_pgs
#### Create temporary page directory and page table and set page
#### directory base register.
# Create page directory at 64 kB and fill with zeroes.
-
mov $0x1000, %ax
mov %ax, %es
subl %eax, %eax
movl $0x400, %ecx
rep stosl
-# Set PDEs for 0 and LOADER_PHYS_BASE to point to the page table.
-# See comments near the PG_* macros in paging.h for a description of
-# the values stored here.
+# Add PDEs to point to PTEs for the first 64 MB of RAM.
+# Also add identical PDEs starting at LOADER_PHYS_BASE.
+# See [IA32-v3a] section 3.7.6 "Page-Directory and Page-Table Entries"
+# for a description of the bits in %eax.
+
movl $0x11007, %eax
- movl %eax, %es:0
- movl %eax, %es:LOADER_PHYS_BASE >> 20
+ movl $0x11, %ecx
+ subl %edi, %edi
+1: movl %eax, %es:(%di)
+ movl %eax, %es:LOADER_PHYS_BASE >> 20(%di)
+ addw $4, %di
+ addl $0x1000, %eax
+ loop 1b
-# Initialize page table.
+# Set up one-to-map linear to physical map for the first 64 MB of RAM.
+# See [IA32-v3a] section 3.7.6 "Page-Directory and Page-Table Entries"
+# for a description of the bits in %eax.
- movl $7, %eax
- movl $0x400, %ecx
-1: stosl
+ movw $0x1100, %ax
+ movw %ax, %es
+ movl $0x7, %eax
+ movl $0x4000, %ecx
+ subl %edi, %edi
+1: movl %eax, %es:(%di)
+ addw $4, %di
addl $0x1000, %eax
loop 1b
#### Switch to protected mode.
-# First we turn off interrupts because we don't set up an IDT.
+# Note that interrupts are still off.
- cli
-
-# Then we point the GDTR to our GDT. Protected mode requires a GDT.
+# 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).
movw %ax, %fs
movw %ax, %gs
movw %ax, %ss
- movl $LOADER_PHYS_BASE + 0x20000, %esp
+ movl $LOADER_PHYS_BASE + 0x30000, %esp
#### Load kernel starting at physical address LOADER_KERN_BASE by
#### frobbing the IDE controller directly.
.long gdt + LOADER_PHYS_BASE # address gdt
#### Fatal error.
-#### Print panicmsg (with help from the BIOS) and spin.
+#### Print panic_message (with help from the BIOS) and spin.
panic: .code16 # We only panic in real mode.
- movw $panicmsg, %si
+ movw $panic_message, %si
movb $0xe, %ah
subb %bh, %bh
1: lodsb
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