Make loader use constants.

diff --git a/src/threads/loader.S b/src/threads/loader.S
index fd8285a16a6589300d40d179dc91f2d650522488..5a0262b58733315296f85ae9ff429711c8d81854 100644 (file)
--- a/src/threads/loader.S
+++ b/src/threads/loader.S
@@ -1,4 +1,5 @@
 #include "mmu.h"
+#include "loader.h"
        
 ##############################################################################
 # Kernel loader.
@@ -60,9 +61,10 @@ 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)
@@ -75,10 +77,11 @@ 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.
@@ -130,25 +133,33 @@ read_sector:
        cmpl $KERNEL_LOAD_PAGES*8 + 1, %ebx
        jnz read_sector
 
-##### Create temporary PDE and PTE and set page directory pointer
+##### Create temporary PDE and PTE, 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 PDE at 64 kB.
+       movl $0x10000, %edi             
        movl %edi, %cr3
+
+       # Fill PDE with zeroes.
        subl %eax, %eax
        movl $0x400, %ecx
        rep stosl
+
+       # Set PDE entries for 0 and LOADER_PHYS_BASE to point to the
+       # PTE.
        movl $0x11000 | PG_U | PG_W | PG_P, %eax
        movl %eax, 0x10000
-       movl %eax, 0x10c00
+       movl %eax, 0x10000 | (LOADER_PHYS_BASE >> 20)
+
+       # Initialize PTE.
        movl $PG_U | PG_W | PG_P, %eax
        movl $0x400, %ecx
 1:     stosl
        addl $0x1000, %eax
        loop 1b
 
-##### Enable paging.
-
+       # Enable paging.
        movl %cr0, %eax
        orl $CR0_PG, %eax
        movl %eax, %cr0
@@ -164,8 +175,8 @@ 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
@@ -194,17 +205,18 @@ panicmsg:
        .ascii "Loader panic!\r\n"
        .byte 0
 
-##### Command-line arguments inserted by another utility.
-##### The loader doesn't use these, but we note their
-##### location here for easy reference.
-       .org 0x200 - 0x80
-cmd_line:      
-
 ##### Memory size in 4 kB pages.
-       .org 0x200 - 6
+       .org LOADER_RAM_PAGES
 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
+cmd_line:
+       .fill 0x80, 1, 0
+
 ##### Boot-sector signature for BIOS inspection.
-       .org 0x200 - 2
+       .org LOADER_BIOS_SIG
        .word 0xaa55

diff --git a/src/threads/loader.h b/src/threads/loader.h
new file mode 100644 (file)
index 0000000..2aebb0f
--- /dev/null
+++ b/src/threads/loader.h
@@ -0,0 +1,22 @@
+#ifndef HEADER_LOADER_H
+#define HEADER_LOADER_H
+
+/* Constants fixed by the PC BIOS. */
+#define LOADER_BASE 0x7c00      /* Physical address of loader's base. */
+#define LOADER_SIZE 0x200       /* Loader size in bytes (one disk sector). */
+
+/* Physical address of kernel base. */
+#define LOADER_KERN_BASE 0x100000       /* 1 MB. */
+
+/* The loader maps 4 MB of the start of physical memory to this
+   virtual base address.  Later, the kernel adds the rest of
+   physical memory to the mapping.
+   This must be aligned on a 4 MB boundary. */
+#define LOADER_PHYS_BASE 0xb0000000     /* 3 GB. */
+
+/* Offsets within the loader. */
+#define LOADER_BIOS_SIG (LOADER_SIZE - 2)        /* aa55 BIOS signature. */
+#define LOADER_CMD_LINE (LOADER_BIOS_SIG - 0x80) /* Kernel command line. */
+#define LOADER_RAM_PAGES (LOADER_CMD_LINE - 4)   /* # of pages of RAM. */
+
+#endif /* loader.h */