From cc1aee9834da1ac35a1ba4337520bde2132fcb4f Mon Sep 17 00:00:00 2001
From: Jeremy Soller <jackpot51@gmail.com>
Date: Wed, 19 Oct 2016 10:06:37 -0600
Subject: [PATCH] Bootloader fixes on systems with wrong CS
---
x86_64/bootsector.asm | 104 +++++++++++++++++---------------------
x86_64/print16.asm | 9 ++--
x86_64/startup-common.asm | 2 +-
3 files changed, 51 insertions(+), 64 deletions(-)
diff --git a/x86_64/bootsector.asm b/x86_64/bootsector.asm
index 806ae49..11ea087 100644
--- a/x86_64/bootsector.asm
+++ b/x86_64/bootsector.asm
@@ -12,6 +12,14 @@ boot: ; dl comes with disk
; initialize stack
mov sp, 0x7C00
+ ; initialize CS
+ push ax
+ push word .set_cs
+ retf
+
+.set_cs:
+
+ ; save disk number
mov [disk], dl
mov si, name
@@ -45,16 +53,16 @@ boot: ; dl comes with disk
; TODO rewrite to (eventually) move larger parts at once
; if that is done increase buffer_size_sectors in startup-common to that (max 0x80000 - startup_end)
load:
- cmp cx, 128
+ cmp cx, 127
jbe .good_size
pusha
- mov cx, 128
+ mov cx, 127
call load
popa
- add ax, 128
- add dx, 128 * 512 / 16
- sub cx, 128
+ add ax, 127
+ add dx, 127 * 512 / 16
+ sub cx, 127
jmp load
.good_size:
@@ -63,31 +71,7 @@ load:
mov [DAPACK.count], cx
mov [DAPACK.seg], dx
- mov bx, [DAPACK.addr + 2]
- call print_num
-
- mov bx, [DAPACK.addr]
- call print_num
-
- mov al, '#'
- call print_char
-
- mov bx, [DAPACK.count]
- call print_num
-
- mov al, ' '
- call print_char
-
- mov bx, [DAPACK.seg]
- call print_num
-
- mov al, ':'
- call print_char
-
- mov bx, [DAPACK.buf]
- call print_num
-
- call print_line
+ call print_dapack
mov dl, [disk]
mov si, DAPACK
@@ -108,16 +92,16 @@ load:
; TODO rewrite to (eventually) move larger parts at once
; if that is done increase buffer_size_sectors in startup-common to that (max 0x80000 - startup_end)
store:
- cmp cx, 128
+ cmp cx, 127
jbe .good_size
pusha
- mov cx, 128
+ mov cx, 127
call store
popa
- add ax, 128
- add dx, 128 * 512 / 16
- sub cx, 128
+ add ax, 127
+ add dx, 127 * 512 / 16
+ sub cx, 127
jmp store
.good_size:
@@ -126,38 +110,41 @@ load:
mov [DAPACK.count], cx
mov [DAPACK.seg], dx
- mov bx, [DAPACK.addr + 2]
- call print_num
+ call print_dapack
+
+ mov dl, [disk]
+ mov si, DAPACK
+ mov ah, 0x43
+ int 0x13
+ jc error
+ ret
- mov bx, [DAPACK.addr]
- call print_num
+print_dapack:
+ mov bx, [DAPACK.addr + 2]
+ call print_num
- mov al, '#'
- call print_char
+ mov bx, [DAPACK.addr]
+ call print_num
- mov bx, [DAPACK.count]
- call print_num
+ mov al, '#'
+ call print_char
- mov al, ' '
- call print_char
+ mov bx, [DAPACK.count]
+ call print_num
- mov bx, [DAPACK.seg]
- call print_num
+ mov al, ' '
+ call print_char
- mov al, ':'
- call print_char
+ mov bx, [DAPACK.seg]
+ call print_num
- mov bx, [DAPACK.buf]
- call print_num
+ mov al, ':'
+ call print_char
- call print_line
+ mov bx, [DAPACK.buf]
+ call print_num
- mov dl, [disk]
- mov si, DAPACK
- mov ah, 0x43
- int 0x13
- jc error
- ret
+ jmp print_line
error:
mov bh, 0
@@ -180,7 +167,6 @@ error:
name: db "Redox Loader - Stage One",0
errored: db "Could not read disk",0
finished: db "Redox Loader - Stage Two",0
-line: db 13,10,0
disk: db 0
diff --git a/x86_64/print16.asm b/x86_64/print16.asm
index 32dc69d..c4a04e1 100644
--- a/x86_64/print16.asm
+++ b/x86_64/print16.asm
@@ -4,7 +4,7 @@ USE16
; a newline
-newline: db 0xD, 0xA, 0
+newline: db 13,10,0
; print a string and a newline
; IN
@@ -13,8 +13,7 @@ newline: db 0xD, 0xA, 0
; ax
print_line:
mov si, newline
- call print
- ret
+ jmp print
; print a string
; IN
@@ -22,11 +21,13 @@ print_line:
; CLOBBER
; ax
print:
+ cld
+.loop:
lodsb
test al, al
jz .done
call print_char
- jmp print
+ jmp .loop
.done:
ret
diff --git a/x86_64/startup-common.asm b/x86_64/startup-common.asm
index 70b9f96..4bb9df7 100644
--- a/x86_64/startup-common.asm
+++ b/x86_64/startup-common.asm
@@ -14,7 +14,7 @@ startup:
; buffersize in multiple of sectors (512 Bytes)
; min 1
; max (0x70000 - startup_end) / 512
-buffer_size_sectors equ 128
+buffer_size_sectors equ 127
; buffer size in Bytes
buffer_size_bytes equ buffer_size_sectors * 512
--
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