X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=src%2Fthreads%2Floader.S;h=4e4fbb4c3e162ace5f0c0d6d1477a92d99e49bbd;hb=6c5c6fdfe80bad40c90c19b67f00226610d59a38;hp=c60e8dd6bd3347551b30f727617b113b88494388;hpb=44d0fa6a2b24a84e5eb0d54959ed91c1d4f15343;p=pintos-anon

diff --git a/src/threads/loader.S b/src/threads/loader.S
index c60e8dd..4e4fbb4 100644
--- a/src/threads/loader.S
+++ b/src/threads/loader.S
@@ -1,15 +1,23 @@
+#include "loader.h"
 #include "mmu.h"
 	
-###################################################################################
-# ENTRY POINT	
-#   This code should be stored in the first sector of the hard disk.  When the  
-#   BIOS runs, it loads this code at physical address 0x7c00 - 0x7e00 (512 bytes).
-#   Then jumps to the beginning of it, in real-mode (BIOS runs in real mode).  
-#	
+##############################################################################
+# Kernel loader.
+#
+# This code should be stored in the first sector of the hard disk.  When the  
+# BIOS runs, it loads this code at physical address 0x7c00-0x7e00 (512 bytes).
+# Then it jumps to the beginning of it, in real mode.  
 # This code switches into protected mode (32-bit mode) so that all of
-# memory can accessed, then calls into C.
-###################################################################################
+# memory can accessed, loads the kernel into memory, and jumps to the
+# first byte of the kernel, where start.S is linked.
+##############################################################################
 	
+/* Flags in control register 0 */
+#define CR0_PE 0x00000001      /* Protection Enable. */
+#define CR0_EM 0x00000004      /* (Floating-point) Emulation. */
+#define CR0_PG 0x80000000      /* Paging. */
+#define CR0_WP 0x00010000      /* Write-Protect enable in kernel mode. */
+
 .globl start				# Entry point	
 start:	.code16				# This runs in real mode
 	cli				# Disable interrupts
@@ -40,12 +48,12 @@ start:	.code16				# This runs in real mode
 #### 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.
 	
-	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
+	movb $0x88,%ah
+	int $0x15
+	jc panic		# Carry flag set on error
+2:	addl $1024,%eax		# Total kB
+	shrl $2,%eax		# Total 4 kB pages
+	movl %eax, ram_pages
 	
 #### switch from real to protected mode	
 ####     The segments in GDT allow all of physical memory to be accessed.
@@ -59,9 +67,10 @@ start:	.code16				# This runs in real mode
 	movl %cr0, %eax		# turn on protected mode
 	orl $CR0_PE, %eax	# 
 	movl %eax, %cr0		# 
-	### CPU magic: jump to relocation, flush prefetch queue, and reload %cs
-	### Has the effect of just jmp to the next instruction, but simultaneous
-	### loads CS with $PROT_MODE_CSEG.
+	### CPU magic: jump to relocation, flush prefetch queue, and
+	### reload %cs Has the effect of just jmp to the next
+	### instruction, but simultaneous loads CS with
+	### $PROT_MODE_CSEG.
 	ljmp $SEL_KCSEG, $protcseg
 	
 #### We are in protected mode in a 32-bit segment (hence the .code32)
@@ -74,10 +83,11 @@ protcseg:
 	movw %ax, %gs		
 	movw %ax, %ss
 
-#### Load kernel at 1 MB by frobbing the IDE controller directly.
+#### Load kernel starting at physical address LOADER_KERN_BASE by
+#### frobbing the IDE controller directly.
 
 	movl $1, %ebx
-	movl $0x100000, %edi
+	movl $LOADER_KERN_BASE, %edi
 read_sector:
 
 	### Poll status register while controller busy.
@@ -129,27 +139,35 @@ read_sector:
 	cmpl $KERNEL_LOAD_PAGES*8 + 1, %ebx
 	jnz read_sector
 
-##### Create temporary PDE and PTE and set page directory pointer
+##### Create temporary page directory and page table, set page
+##### directory pointer, and turn on paging.
 ##### FIXME? We could use a single 4 MB page instead of 1024 4 kB pages.
 
-	movl $0x10000, %edi
+	# Create page directory at 64 kB.
+	movl $0x10000, %edi		
 	movl %edi, %cr3
+
+	# Fill page directory with zeroes.
 	subl %eax, %eax
 	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, 0x10000
-	movl %eax, 0x10c00
+	movl %eax, 0x10000 | (LOADER_PHYS_BASE >> 20)
+
+	# Initialize page table.
 	movl $PG_U | PG_W | PG_P, %eax
 	movl $0x400, %ecx
 1:	stosl
 	addl $0x1000, %eax
 	loop 1b
 
-##### Enable paging.
-
+	# Turn on paging and kernel write-protect.
 	movl %cr0, %eax
-	orl $CR0_PG, %eax
+	orl $CR0_PG | CR0_WP, %eax
 	movl %eax, %cr0
 	jmp 1f
 1:
@@ -163,8 +181,8 @@ read_sector:
 	
 ##### Jump to kernel entry point.
 
-	movl $0xc0007c00, %esp
-	movl $0xc0100000, %eax
+	movl $LOADER_PHYS_BASE + LOADER_BASE, %esp
+	movl $LOADER_PHYS_BASE + LOADER_KERN_BASE, %eax
 	jmp *%eax
 
 ##### GDT
@@ -178,14 +196,33 @@ gdtdesc:
 	.word	0x17			# sizeof (gdt) - 1
 	.long	gdt			# address gdt
 
-##### Arrive here on error
-panic:	jmp panic
+##### To panic, we print panicmsg (with help from the BIOS) and spin.
+panic:  .code16			# We only panic in real mode.
+	movw $panicmsg, %si
+	movb $0xe, %ah
+	xorb %bh, %bh
+1:	lodsb
+	test %al, %al
+2:	jz 2b			# Spin.
+	int $0x10
+	jmp 1b
+
+panicmsg:
+	.ascii "Loader panic!\r\n"
+	.byte 0
 
 ##### Memory size in 4 kB pages.
-	.org 0x200 - 8
+	.org LOADER_RAM_PAGES - LOADER_BASE
 ram_pages:
 	.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:
+	.fill 0x80, 1, 0
+
 ##### Boot-sector signature for BIOS inspection.
-	.org 0x200 - 2
+	.org LOADER_BIOS_SIG - LOADER_BASE
 	.word 0xaa55