load stage2 high to leave the low RAM for the kernel

diff --git a/.gitignore b/.gitignore
index 3576cff..77c7ebc 100644 (file)
--- a/.gitignore
+++ b/.gitignore
@@ -3,5 +3,6 @@
 *.swp
 *.img
 *.map
-dis
+dis1
+dis2
 *.log

diff --git a/Makefile b/Makefile
index 0bac632..8e95cce 100644 (file)
--- a/Makefile
+++ b/Makefile
@@ -26,4 +26,5 @@ debug: $(bin)
 
 .PHONY: disasm
 disasm: $(bin)
-       ndisasm -o 0x7c00 $< >dis
+       ndisasm -o 0x7c00 $< >dis1
+       ndisasm -o 0x80000 -e 512 $< >dis2

diff --git a/boot.ld b/boot.ld
index b607e11..99bc701 100644 (file)
--- a/boot.ld
+++ b/boot.ld
@@ -6,10 +6,13 @@ SECTIONS {
        .bootsect : {
                * (.bootsect);
        }
+       _bootsect_end = .;
 
-       . = 0x7e00;
+       /* load high out of the way, to allow stage2 to load the kernel low */
+       . = 0x80000;
        _stage2_start = .;
-       .text : {
+       _stage2_start_seg = _stage2_start >> 4;
+       .text : AT(_bootsect_end) {
                * (.startup);
                * (.text*);
        }
@@ -19,6 +22,7 @@ SECTIONS {
        }
        .bss ALIGN(4) (NOLOAD): {
                _bss_start = .;
+               _bss_start_off = _bss_start - _stage2_start;
                * (.bss*);
                * (COMMON);
                . = ALIGN(4);
@@ -26,4 +30,5 @@ SECTIONS {
        _bss_size = SIZEOF(.bss);
        . = ALIGN(4);
        _stage2_end = .;
+       _stage2_size = _stage2_end - _stage2_start;
 };

diff --git a/boot/boot.asm b/boot/boot.asm
index 5b82c2d..2b74db8 100644 (file)
--- a/boot/boot.asm
+++ b/boot/boot.asm
@@ -3,10 +3,9 @@
        bits 16
        section .bootsect
 
-extern _stage2_start
-extern _stage2_end
+extern _stage2_start_seg
+extern _stage2_size
 
-stacktop       equ 7b00h
 boot_driveno   equ 7b00h
 num_read_tries equ 7b06h       ; 2 bytes
 sect_pending   equ 7b08h       ; 2 bytes
@@ -58,12 +57,12 @@ start:
        xor ax, ax
        mov ds, ax
        mov es, ax
-       mov ss, ax
-       mov gs, ax
-       mov fs, ax
        jmp 00:.setcs
 .setcs:
-       mov sp, stacktop
+       ; put the stack high
+       mov ax, 0x7f00
+       mov ss, ax
+       xor sp, sp
        mov [boot_driveno], dl
 
        ; query sectors per track
@@ -84,20 +83,15 @@ start:
        mov word [num_heads], 2
 .querydone:
 
-; load the rest of the code at 7e00h
-       mov ax, _stage2_end
-       sub ax, _stage2_start
+       ; load the rest of the code high
+       mov ax, _stage2_size
        add ax, 511
        mov cl, 9
        shr ax, cl
        inc ax
        mov [sect_pending], ax
-       mov ax, _stage2_start
-       shr ax, 1
-       shr ax, 1
-       shr ax, 1
-       shr ax, 1
-       mov es, ax      ; destination segment 7e0h to allow loading up to 64k
+       mov ax, _stage2_start_seg
+       mov es, ax      ; destination segment
        mov word [destptr], 0
        mov word [start_sect], 1        ; start from sector 1 to skip boot sector
        mov word [cur_cyl], 0
@@ -170,10 +164,15 @@ start:
        add [destptr], ax
        jnz .rdloop
 
-       ; loaded sucessfully, reset es back to 0 and jump
-.done: xor ax, ax
+       ; loaded sucessfully, load segment registers and jump
+.done: mov ax, _stage2_start_seg
+       mov ds, ax
        mov es, ax
-       jmp _stage2_start
+       push ax
+       xor ax, ax
+       push ax
+       retf
+
 
 .fail: add sp, 2       ; clear num_sect off the stack
        dec word [num_read_tries]

diff --git a/boot/boot2.asm b/boot/boot2.asm
index 6837579..c90cef6 100644 (file)
--- a/boot/boot2.asm
+++ b/boot/boot2.asm
@@ -4,15 +4,25 @@
        section .startup
 
 extern bootmain
+extern _stage2_start_seg
+extern _bss_start_off
+extern _bss_size
 
 global _start
 _start:
        ; TODO floppy off if necessary
-       ; TODO zero .bss
+
+       ; zero .bss
+       mov di, _bss_start_off
+       mov cx, _bss_size
+       shr cx, 1
+       rep stosw
+       xor ax, ax
+       mov es, ax
+
        call bootmain
 
 hang:  hlt
        jmp hang
 
-
 ; vi:set ts=8 sts=8 sw=8 ft=nasm: