X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=src%2Fthreads%2Floader.S;h=d1e8309c5f194ec47ca996cf7c7c00fae1e96013;hb=768b68e1186555add74471639fd41f1ce3f12d8b;hp=704b1d9b2f76a93e3d2e20a31b375562a22f65b9;hpb=f31b7fd0769b818f910546ec97284cceb7450593;p=pintos-anon

diff --git a/src/threads/loader.S b/src/threads/loader.S
index 704b1d9..d1e8309 100644
--- a/src/threads/loader.S
+++ b/src/threads/loader.S
@@ -39,7 +39,6 @@
  */
 
 #include "threads/loader.h"
-#include "threads/mmu.h"
 	
 #### Kernel loader.
 
@@ -51,7 +50,7 @@
 #### 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. */
@@ -59,6 +58,8 @@
 
 # Code runs in real mode, which is a 16-bit segment.
 
+.globl start
+start:
 	.code16
 
 # Disable interrupts.
@@ -109,20 +110,23 @@
 #### 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
+	jc panic
+	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_pages
 	
 #### 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
@@ -130,17 +134,29 @@
 	movl $0x400, %ecx
 	rep stosl
 
-# Set PDEs for 0 and LOADER_PHYS_BASE to point to the page table.
+# 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.
 
-	movl $0x11000 | PG_U | PG_W | PG_P, %eax
-	movl %eax, %es:0
-	movl %eax, %es:LOADER_PHYS_BASE >> 20
+	movl $0x11007, %eax
+	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-v3] section 3.7.6 for a description of the bits in %eax.
 
-	movl $PG_U | PG_W | PG_P, %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
 
@@ -194,7 +210,7 @@
 	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.
@@ -251,9 +267,9 @@ read_sector:
 
 # Transfer sector.
 
-	movl $512 / 4, %ecx
+	movl $256, %ecx
 	movl $0x1f0, %edx
-	rep insl
+	rep insw
 
 # Next sector.