Work on loader to prepare for passing in a command line.

[pintos-anon] / src / threads / loader.S

diff --git a/src/threads/loader.S b/src/threads/loader.S
index c60e8dd6bd3347551b30f727617b113b88494388..fd8285a16a6589300d40d179dc91f2d650522488 100644 (file)
--- a/src/threads/loader.S
+++ b/src/threads/loader.S
@@ -1,14 +1,15 @@
 #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.
+##############################################################################
        
 .globl start                           # Entry point   
 start: .code16                         # This runs in real mode
@@ -40,12 +41,12 @@ 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.
@@ -178,11 +179,29 @@ 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
+
+##### 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 - 8
+       .org 0x200 - 6
 ram_pages:
        .long 0