relocate code sections to end up with stage2 starting at 0x500
This commit is contained in:
@@ -21,10 +21,10 @@
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%ifndef __INC_ENTRY
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; 8KiB from 0x2500 -> 0x500
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%define EARLY_STACK_START 0x2500
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%define EARLY_STACK_START 0xFFFF
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%define MBR_ENTRY 0x0600
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%define VBR_ENTRY 0x7C00
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%define STAGE2_ENTRY 0x7E00
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%define STAGE2_ENTRY 0x0500
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%endif
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%define __INC_ENTRY
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@@ -42,16 +42,18 @@ nop
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ALIGN 4
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init:
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cli ; We do not want to be interrupted
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cli ; We do not want to be interrupted
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xor ax, ax ; 0 AX
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mov ds, ax ; Set segment registers to 0
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mov ss, ax ; Set Stack Segment to 0
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mov sp, EARLY_STACK_START ; Setup stack
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mov bp, sp ; base ptr = stack ptr
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sub sp, 0x20 ; local varible space
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xor ax, ax ; 0 AX
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mov ds, ax ; Set segment registers to 0
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mov es, ax
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mov ss, ax ; Set Stack Segment to 0
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mov sp, EARLY_STACK_START ; Setup stack
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mov bp, sp ; base ptr = stack ptr
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sub sp, 0x10 ; local varible space
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xor cx, cx
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mov ch, 0x01 ; 256 WORDs in MBR (512 bytes), 0x0100 in cx
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mov si, 0x7C00 ; Current MBR Address (loaded here by BIOS)
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mov di, MBR_ENTRY ; New MBR Address (our new relocation address)
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@@ -115,12 +117,11 @@ main:
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mov dword eax, dword [bx + PartEntry_t.lba_start]
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push dword eax ; lba
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xor ax, ax
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push ax ; offset = 0
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mov ax, VBR_ENTRY
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shr ax, 4
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push ax ; segment = 7C0
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push ax ; offset = 0x7c00
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xor ax, ax
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push ax ; segment = 0
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; uint8_t read_stage2_raw(uint16_t buf_segment, uint16_t buf_offset,
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; uint32_t lba,
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@@ -19,7 +19,7 @@
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; SOFTWARE.
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[BITS 16]
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[ORG 0x7E00]
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[ORG 0x0500] ; IF YOU CHANGE ORG CHANGE THE SIGN OFFSET AT THE END
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[CPU KATMAI]
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[map all stage2.map]
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[WARNING -reloc-abs-byte]
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@@ -47,7 +47,7 @@
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%endmacro
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section .text
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org 0x7E00
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org 0x0500
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begin_text:
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jmp short (init - $$)
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@@ -57,6 +57,18 @@ ALIGN 4, db 0x90
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init:
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cli ; We do not want to be interrupted
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mov cx, (end_bss - begin_bss) ; count = bss length
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mov ax, begin_bss
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shr ax, 4
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mov es, ax ; es = begining of bss section
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xor ax, ax
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mov di, ax ; dst = 0
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cld
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rep stosb ; zero bss section
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mov ax, __STAGE2_SEGMENT ; configured segment
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mov ds, ax ; Set segment registers to 0
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mov es, ax ; *
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@@ -128,11 +140,8 @@ main:
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mov eax, dword [STAGE2_SIG]
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cmp eax, 0xDEADBEEF
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je main.bss_init
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je main.stage2_main
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ERROR STAGE2_SIGNATURE_MISSING
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.bss_init:
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nop ; placeholder
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.stage2_main:
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call SetTextMode
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call disable_cursor
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@@ -396,8 +405,9 @@ unreal_gdt_start:
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dw 0xFFFF ; Segment Limit 15:0
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dw 0x0000 ; Base Address 15:0
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db 0000_0000b ; Base Address 23:16
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db 1001_1010b ; Access Byte: executable, readable, present
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db 0000_1111b ; Flags: 16-bit, Granularity = 4KiB
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db 1000_1111b ; 24:20 G/DB/L/AVL & SegLimit 19:16
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db 0000_0000b ; Base Address 31:24
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; entry 2 (16-bit data segment with 4 GiB flat mapping)
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@@ -405,7 +415,7 @@ unreal_gdt_start:
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dw 0x0000 ; Base Address 15:0
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db 0000_0000b ; Base Address 23:16
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db 1001_0010b ; Access Byte: readable, writable, present
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db 0000_1111b ; Flags: 16-bit, Granularity = 4KiB
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db 1000_1111b ; Flags: 16-bit, Granularity = 4KiB
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db 0000_0000b ; Base Address 31:24
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unreal_gdt_end:
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@@ -459,7 +469,7 @@ end_data:
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; section start location needs to be a 'critical expression'
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; i.e resolvable at build time, we are setting 0x7E00 as the offset since
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section .sign start=((MAX_STAGE2_BYTES - 512) + 0x7E00)
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section .sign start=((MAX_STAGE2_BYTES - 512) + 0x0500)
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times ((512 - 4) - ($ -$$) ) db 0x90 ; nop
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STAGE2_SIG: dd 0xDEADBEEF ; Signature to mark the end of the stage2
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@@ -474,7 +484,6 @@ stage2_main_redzone resb 32
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SteviaInfo resd 4
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fat32_state resb FAT32_State_t_size
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align 512
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disk_buffer resb 512
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fat_buffer resb 512
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@@ -115,13 +115,12 @@ main:
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mov dword eax, 0x1
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push dword eax ; lba
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xor ax, ax
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push ax ; offset = 0
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; 07E0:0 = 0x00007e00
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mov ax, STAGE2_ENTRY
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shr ax, 4
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push ax ; segment = 7E0
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push ax ; offset
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xor ax, ax
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push ax ; segment = 0
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; uint8_t read_stage2_raw(uint16_t buf_segment, uint16_t buf_offset,
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; uint32_t lba,
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@@ -130,11 +129,8 @@ main:
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add sp, 0xC
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.check_sig:
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; BUG: this is hard coded to check @ ((0x7E0 << 4) + 0x7FFC)...i.e (STAGE2_ENTRY + (STAGE2_MAX_BYTES - 4))
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; this should be removed or done properly
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mov ax, 0x7E0
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mov fs, ax
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cmp dword [fs:0x7FFC], 0xDEADBEEF
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mov eax, dword [(MAX_STAGE2_BYTES - 4) + 0x500]
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cmp eax, 0xDEADBEEF
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je main.sig_ok
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ERROR VBR_ERROR_NO_SIGNATURE ; no signature present in stage2
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@@ -142,7 +138,7 @@ main:
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.sig_ok:
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mov si, word [bp - 4]
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mov dl, byte [bp - 2]
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jmp word 0x0000:0x7E00
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jmp word 0x0000:STAGE2_ENTRY
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; ###############
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; Required BIOS function(s)
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