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relocate code sections to end up with stage2 starting at 0x500

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Elaina Claus
2024-10-12 22:14:47 -04:00
parent 3d3bcc6ea5
commit bd40d6d324
4 changed files with 42 additions and 36 deletions
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4
include/entry.inc
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@@ -21,10 +21,10 @@
%ifndef __INC_ENTRY %ifndef __INC_ENTRY
; 8KiB from 0x2500 -> 0x500 ; 8KiB from 0x2500 -> 0x500
%define EARLY_STACK_START 0x2500 %define EARLY_STACK_START 0xFFFF
%define MBR_ENTRY 0x0600 %define MBR_ENTRY 0x0600
%define VBR_ENTRY 0x7C00 %define VBR_ENTRY 0x7C00
%define STAGE2_ENTRY 0x7E00 %define STAGE2_ENTRY 0x0500
%endif %endif
%define __INC_ENTRY %define __INC_ENTRY

27
src/mbr/mbr.nasm
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@@ -42,16 +42,18 @@ nop
ALIGN 4 ALIGN 4
init: init:
cli ; We do not want to be interrupted cli ; We do not want to be interrupted
xor ax, ax ; 0 AX xor ax, ax ; 0 AX
mov ds, ax ; Set segment registers to 0 mov ds, ax ; Set segment registers to 0
mov es, ax
mov ss, ax ; Set Stack Segment to 0
mov sp, EARLY_STACK_START ; Setup stack mov ss, ax ; Set Stack Segment to 0
mov bp, sp ; base ptr = stack ptr mov sp, EARLY_STACK_START ; Setup stack
sub sp, 0x20 ; local varible space mov bp, sp ; base ptr = stack ptr
sub sp, 0x10 ; local varible space
xor cx, cx
mov ch, 0x01 ; 256 WORDs in MBR (512 bytes), 0x0100 in cx mov ch, 0x01 ; 256 WORDs in MBR (512 bytes), 0x0100 in cx
mov si, 0x7C00 ; Current MBR Address (loaded here by BIOS) mov si, 0x7C00 ; Current MBR Address (loaded here by BIOS)
mov di, MBR_ENTRY ; New MBR Address (our new relocation address) mov di, MBR_ENTRY ; New MBR Address (our new relocation address)
@@ -115,12 +117,11 @@ main:
mov dword eax, dword [bx + PartEntry_t.lba_start] mov dword eax, dword [bx + PartEntry_t.lba_start]
push dword eax ; lba push dword eax ; lba
xor ax, ax
push ax ; offset = 0
mov ax, VBR_ENTRY mov ax, VBR_ENTRY
shr ax, 4 push ax ; offset = 0x7c00
push ax ; segment = 7C0
xor ax, ax
push ax ; segment = 0
; uint8_t read_stage2_raw(uint16_t buf_segment, uint16_t buf_offset, ; uint8_t read_stage2_raw(uint16_t buf_segment, uint16_t buf_offset,
; uint32_t lba, ; uint32_t lba,

29
src/stage2/stage2.nasm
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@@ -19,7 +19,7 @@
; SOFTWARE. ; SOFTWARE.
[BITS 16] [BITS 16]
[ORG 0x7E00] [ORG 0x0500] ; IF YOU CHANGE ORG CHANGE THE SIGN OFFSET AT THE END
[CPU KATMAI] [CPU KATMAI]
[map all stage2.map] [map all stage2.map]
[WARNING -reloc-abs-byte] [WARNING -reloc-abs-byte]
@@ -47,7 +47,7 @@
%endmacro %endmacro
section .text section .text
org 0x7E00 org 0x0500
begin_text: begin_text:
jmp short (init - $$) jmp short (init - $$)
@@ -57,6 +57,18 @@ ALIGN 4, db 0x90
init: init:
cli ; We do not want to be interrupted cli ; We do not want to be interrupted
mov cx, (end_bss - begin_bss) ; count = bss length
mov ax, begin_bss
shr ax, 4
mov es, ax ; es = begining of bss section
xor ax, ax
mov di, ax ; dst = 0
cld
rep stosb ; zero bss section
mov ax, __STAGE2_SEGMENT ; configured segment mov ax, __STAGE2_SEGMENT ; configured segment
mov ds, ax ; Set segment registers to 0 mov ds, ax ; Set segment registers to 0
mov es, ax ; * mov es, ax ; *
@@ -128,11 +140,8 @@ main:
mov eax, dword [STAGE2_SIG] mov eax, dword [STAGE2_SIG]
cmp eax, 0xDEADBEEF cmp eax, 0xDEADBEEF
je main.bss_init je main.stage2_main
ERROR STAGE2_SIGNATURE_MISSING ERROR STAGE2_SIGNATURE_MISSING
.bss_init:
nop ; placeholder
.stage2_main: .stage2_main:
call SetTextMode call SetTextMode
call disable_cursor call disable_cursor
@@ -396,8 +405,9 @@ unreal_gdt_start:
dw 0xFFFF ; Segment Limit 15:0 dw 0xFFFF ; Segment Limit 15:0
dw 0x0000 ; Base Address 15:0 dw 0x0000 ; Base Address 15:0
db 0000_0000b ; Base Address 23:16 db 0000_0000b ; Base Address 23:16
db 1001_1010b ; Access Byte: executable, readable, present db 1001_1010b ; Access Byte: executable, readable, present
db 0000_1111b ; Flags: 16-bit, Granularity = 4KiB db 1000_1111b ; 24:20 G/DB/L/AVL & SegLimit 19:16
db 0000_0000b ; Base Address 31:24 db 0000_0000b ; Base Address 31:24
; entry 2 (16-bit data segment with 4 GiB flat mapping) ; entry 2 (16-bit data segment with 4 GiB flat mapping)
@@ -405,7 +415,7 @@ unreal_gdt_start:
dw 0x0000 ; Base Address 15:0 dw 0x0000 ; Base Address 15:0
db 0000_0000b ; Base Address 23:16 db 0000_0000b ; Base Address 23:16
db 1001_0010b ; Access Byte: readable, writable, present db 1001_0010b ; Access Byte: readable, writable, present
db 0000_1111b ; Flags: 16-bit, Granularity = 4KiB db 1000_1111b ; Flags: 16-bit, Granularity = 4KiB
db 0000_0000b ; Base Address 31:24 db 0000_0000b ; Base Address 31:24
unreal_gdt_end: unreal_gdt_end:
@@ -459,7 +469,7 @@ end_data:
; section start location needs to be a 'critical expression' ; section start location needs to be a 'critical expression'
; i.e resolvable at build time, we are setting 0x7E00 as the offset since ; i.e resolvable at build time, we are setting 0x7E00 as the offset since
section .sign start=((MAX_STAGE2_BYTES - 512) + 0x7E00) section .sign start=((MAX_STAGE2_BYTES - 512) + 0x0500)
times ((512 - 4) - ($ -$$) ) db 0x90 ; nop times ((512 - 4) - ($ -$$) ) db 0x90 ; nop
STAGE2_SIG: dd 0xDEADBEEF ; Signature to mark the end of the stage2 STAGE2_SIG: dd 0xDEADBEEF ; Signature to mark the end of the stage2
@@ -474,7 +484,6 @@ stage2_main_redzone resb 32
SteviaInfo resd 4 SteviaInfo resd 4
fat32_state resb FAT32_State_t_size fat32_state resb FAT32_State_t_size
align 512
disk_buffer resb 512 disk_buffer resb 512
fat_buffer resb 512 fat_buffer resb 512

18
src/vbr/vbr.nasm
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@@ -115,13 +115,12 @@ main:
mov dword eax, 0x1 mov dword eax, 0x1
push dword eax ; lba push dword eax ; lba
xor ax, ax
push ax ; offset = 0
; 07E0:0 = 0x00007e00
mov ax, STAGE2_ENTRY mov ax, STAGE2_ENTRY
shr ax, 4 push ax ; offset
push ax ; segment = 7E0
xor ax, ax
push ax ; segment = 0
; uint8_t read_stage2_raw(uint16_t buf_segment, uint16_t buf_offset, ; uint8_t read_stage2_raw(uint16_t buf_segment, uint16_t buf_offset,
; uint32_t lba, ; uint32_t lba,
@@ -130,11 +129,8 @@ main:
add sp, 0xC add sp, 0xC
.check_sig: .check_sig:
; BUG: this is hard coded to check @ ((0x7E0 << 4) + 0x7FFC)...i.e (STAGE2_ENTRY + (STAGE2_MAX_BYTES - 4)) mov eax, dword [(MAX_STAGE2_BYTES - 4) + 0x500]
; this should be removed or done properly cmp eax, 0xDEADBEEF
mov ax, 0x7E0
mov fs, ax
cmp dword [fs:0x7FFC], 0xDEADBEEF
je main.sig_ok je main.sig_ok
ERROR VBR_ERROR_NO_SIGNATURE ; no signature present in stage2 ERROR VBR_ERROR_NO_SIGNATURE ; no signature present in stage2
@@ -142,7 +138,7 @@ main:
.sig_ok: .sig_ok:
mov si, word [bp - 4] mov si, word [bp - 4]
mov dl, byte [bp - 2] mov dl, byte [bp - 2]
jmp word 0x0000:0x7E00 jmp word 0x0000:STAGE2_ENTRY
; ############### ; ###############
; Required BIOS function(s) ; Required BIOS function(s)