Merge pull request #3 from Nivirx/bss-setup

convert MBR, VBR, & Stage2 to use a BSS section.

Makefile

@@ -25,6 +25,7 @@ stage2: $(stage2_binary_files)
 boottest: $(boottest_binary_files)
 
 clean:
+	@rm -rvf *.map
 	@rm -rvf $(build_dir)/*
 	@rm -rvf $(iso)
 	@rm -rvf $(isoz)

include/BIOS/func/E820_memory_map.nasm

@@ -48,7 +48,8 @@ GetMemoryMap:
     mov eax, 0xE820                         ; select 0xE820 function
     xor ebx, ebx                            ; Continuation value, 0 for the first call
 
-    mov dx, (BIOSMemoryMap >> 4)
+    lea dx, [BIOSMemoryMap]
+    shr dx, 4
     mov es, dx
     xor di, di                              ; (BIOSMemoryMap >> 4):0 makes di an index into BIOSMemoryMap
 

include/BIOS/func/ext_read.nasm

@@ -36,6 +36,29 @@ struc LBAPkt_t
     .lower_lba   resd 1
     .upper_lba   resd 1
 endstruc
+; call_read_disk_raw <word segment> <word offset> <dword lba> <word count> <word drive_num>
+%macro call_read_disk_raw 5
+    movzx ax, %5
+    push ax                                            ; drive_num
+
+    movzx ax, %4
+    push ax                                            ; count
+
+    movzx dword eax, %3
+    push dword eax                                     ; lba
+
+    movzx ax, %2
+    push ax                                            ; offset
+
+    movzx ax, %1
+    push ax                                            ; segment = 0
+
+    ; uint8_t read_stage2_raw(uint16_t buf_segment, uint16_t buf_offset, 
+    ;                         uint32_t lba,
+    ;                         uint16_t count, uint16_t drive_num)
+    call read_disk_raw
+    add sp, 0xC
+%endmacro
 
 ; Wrapper for AH=0x42 INT13h (Extended Read)
 ;

include/config.inc

@@ -21,7 +21,7 @@
 %ifndef __INC_STEVIA_CONFIG
 
 %define SECTOR_SIZE             512
-%define STAGE2_SECTOR_COUNT    0x40
+%define STAGE2_SECTOR_COUNT    0x30
 ; 32 KiB
 %define MAX_STAGE2_BYTES      (SECTOR_SIZE * STAGE2_SECTOR_COUNT)
 

include/early_mem.inc

@@ -18,7 +18,7 @@
 ; OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 ; SOFTWARE.
 
-%ifndef __INC_MEM
+%ifndef __INC_EARLY_MEM
 
 
 ; ## Generic Low mem map (from osdev wiki) ##
@@ -43,54 +43,6 @@
 ; 0x0000000100000000  	    ???	            ??? (whatever exists) 	    RAM -- free for use (PAE/64bit)/More Extended memory
 ; ???????????????? 	        ??? 	        ??? 	                    Potentially usable for memory mapped PCI devices in modern hardware (but typically not, due to backward compatibility) 
 
-; 0x2700 -> 0x28FF
-%define disk_buffer           0x2700
-; 0x2900 -> 0x2AFF
-%define fat_buffer            0x2900
-; 0x2B00 -> 0x2CFF
-%define dir_buffer            0x2B00
-
-; copy of partition table, 72 bytes
-%define partition_table       0x3000
-%define partition_table_SIZE  72
-
-; copy of FAT32 BPB, 33 bytes (+1 to the next value to align to uint16_t)
-;0x3048
-%define fat32_bpb             0x304A
-%define fat32_bpb_SIZE        36
-
-; copy of FAT32 EBPB, 54 bytes
-;0x306A
-%define fat32_ebpb            0x306E
-%define fat32_ebpb_SIZE       54
-
-; FAT32 FSInfo, 512 bytes
-;0x30A2
-%define fat32_fsinfo          0x30B0
-%define fat32_fsinfo_SIZE     512
-
-; some stored state for the fat32 driver
-;0x32A2
-%define fat32_state           0x34B0
-%define fat32_state_SIZE      32
-
-; next free space is 0x32D0
-%define fat32_nc_data         0x35D0
-%define fat32_nc_data_size    16
-
-; lba_packet for raw_disk_read
-%define lba_packet            0x4000
-
-%define BIOSMemoryMap         0x4200
-%define SteviaInfo            0x5200
-
-
-; High memory addresses for loading kernel (for use with unreal mode and 32bit override)
-
-; file load buffer at 16MB
-%define HMEM_load_buffer      0x1000000
-
-
 ;PhysicalAddress = Segment * 16 + Offset
 %define SEG_TO_LINEAR(s,o) ((s << 4) + o)
 
@@ -100,17 +52,5 @@
 ; Seg = (physical - offset) / 16
 %define LINEAR_TO_SEGMENT(p,o) ((p - o) >> 4)
 
-; create normalized linear addres from seg:off (16:4)
-; Segement = linear >> 4 (top 16 bits)
-; offset = linear & 0x0F (low 4 bits)
-
-; 20 bytes, passed to loaded kernel
-struc SteviaInfoStruct_t
-    .MemoryMapPtr      resd 1
-    .MemoryMapEntries  resd 1
-    .BPBDataPtr        resd 1
-    .EBPBDataPtr       resd 1
-endstruc
-
 %endif
-%define __INC_MEM
+%define __INC_EARLY_MEM

include/entry.inc

@@ -21,10 +21,10 @@
 %ifndef __INC_ENTRY
 
 ; 8KiB from 0x2500 -> 0x500
-%define EARLY_STACK_START            0x2500
+%define EARLY_STACK_START            0xFFFF
-%define MBR_ENTRY                    0x7A00
+%define MBR_ENTRY                    0x0600
 %define VBR_ENTRY                    0x7C00
-%define STAGE2_ENTRY                 0x7E00
+%define STAGE2_ENTRY                 0x0500
 
 %endif
 %define __INC_ENTRY

include/fat32/FAT32_SYS.inc

@@ -28,7 +28,7 @@ ALIGN 4, db 0x90
 InitFATDriver:
     __CDECL16_ENTRY
 .func:
-    mov ax, fat32_state_SIZE
+    mov ax, FAT32_State_t_size
     push ax                     ; length of fat32_state structure
     xor ax, ax
     push ax                     ; init fat32_state with zero

include/fat32/fat32_structures.inc

@@ -63,6 +63,7 @@
 ;                           resulting in a value which does not fit in the Number of Sectors entry at 0x13. 
 
 struc FAT32_bpb_t
+    .reserved_init             resb 3
     .ident_8                   resb 8
     .bytes_per_sector_16       resb 2
     .sectors_per_cluster_8     resb 1

include/partition_table.inc

@@ -34,15 +34,15 @@ struc PartEntry_t
     .chs_start  resb 3
     .part_type  resb 1
     .chs_end    resb 3
-    .lba_start  resb 4
+    .lba_start  resd 1
-    .lba_length resb 4
+    .lba_length resd 1
 endstruc
 
 struc PartTable_t
-    .partition1 resb 16
+    .partition1 resb PartEntry_t_size
-    .partition2 resb 16
+    .partition2 resb PartEntry_t_size
-    .partition3 resb 16
+    .partition3 resb PartEntry_t_size
-    .partition4 resb 16
+    .partition4 resb PartEntry_t_size
 endstruc
 
 %endif

include/util/error_func.nasm

@@ -22,9 +22,7 @@
 
 %macro ERROR 1
     mov al, %1           ; al = 1 byte error code mapped to ascii values
-    db 0xEA              ; jmp far imm16:imm16
+    jmp error
-    dw error             ; error_far_seg
-    dw 0x0000            ; error_far_ptr
 %endmacro
 
 ; pass error as ascii character in al, errors a-zA-Z or 0-9

include/util/kmemcpy5_func.nasm

@@ -0,0 +1,53 @@
+; Copyright (c) 2024 Elaina Claus
+;
+; Permission is hereby granted, free of charge, to any person obtaining a copy
+; of this software and associated documentation files (the "Software"), to deal
+; in the Software without restriction, including without limitation the rights
+; to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+; copies of the Software, and to permit persons to whom the Software is
+; furnished to do so, subject to the following conditions:
+;
+; The above copyright notice and this permission notice shall be included in all
+; copies or substantial portions of the Software.
+;
+; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+; IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+; FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+; AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+; LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+; OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+; SOFTWARE.
+
+%ifndef __INC_KMEMCPY5_FUNC
+%include 'cdecl16.inc'
+
+; uint8_t* kmemset(word dest_segment, word dest, word src_segment, word src, byte len);
+; not overlap safe, only for
+ALIGN 4, db 0x90
+kmemcpy5:
+    __CDECL16_ENTRY
+    push ds
+    push es
+.setup_segments:
+    mov ax, [bp + 4]
+    mov ds, ax              ; destination segment
+
+    mov ax, [ bp + 8]
+    mov es, ax              ; source segment
+.func:
+    mov cx, [bp + 12]        ; len
+    mov si, [bp + 10]        ; src
+    mov di, [bp + 6]        ; dest
+    
+    cld                     ; ensure we are incrementing
+    rep movsb               ; move ds:si -> es:di
+    mov ax, di              ; return pointer to dest
+.restore_segments:
+    pop es
+    pop ds
+.endf:
+    __CDECL16_EXIT
+    ret
+
+%define __INC_KMEMCPY5_FUNC
+%endif

include/util/kmemset4_func.nasm

@@ -0,0 +1,47 @@
+; Copyright (c) 2024 Elaina Claus
+;
+; Permission is hereby granted, free of charge, to any person obtaining a copy
+; of this software and associated documentation files (the "Software"), to deal
+; in the Software without restriction, including without limitation the rights
+; to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+; copies of the Software, and to permit persons to whom the Software is
+; furnished to do so, subject to the following conditions:
+;
+; The above copyright notice and this permission notice shall be included in all
+; copies or substantial portions of the Software.
+;
+; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+; IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+; FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+; AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+; LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+; OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+; SOFTWARE.
+
+%ifndef __INC_KMEMSET4_FUNC
+%include 'cdecl16.inc'
+
+; word kmemset_byte(word segment, word dst, byte val, word len);
+ALIGN 4, db 0x90
+kmemset4:
+    __CDECL16_ENTRY
+.setup_segment:
+    push es
+    mov ax, [bp + 4]
+    mov es, ax
+ .func:
+    mov     cx, [bp + 10]       ; size_t len
+    mov     al, [bp + 8]        ; uint8_t val
+    mov     di, [bp + 6]        ; word dst
+
+    cld
+    rep     stosb               ; move al -> es:di
+    mov     ax, di              ; return pointer to dest
+.restore_segments:
+    pop es
+.endf:
+    __CDECL16_EXIT
+    ret
+
+%endif
+%define __INC_KMEMSET4_FUNC

src/mbr/mbr.nasm

@@ -19,46 +19,51 @@
 ; SOFTWARE.
 
 [BITS 16]
-[ORG 0x7A00]
+[ORG 0x0600]
 [CPU KATMAI]
 [WARNING -reloc-abs-byte]
 [WARNING -reloc-abs-word]                   ; Yes, we use absolute addresses. surpress these warnings.
 [map all mbr.map]
 %define __STEVIA_MBR
-
 jmp short (init - $$)
 nop
 
 ; ###############
-;
 ; Headers/Includes/Definitions
-;
 ; ###############
 
 %include "util/bochs_magic.inc"
 %include "cdecl16.inc"
 %include "entry.inc"
 %include "config.inc"
-%include "mem.inc"
 %include "error_codes.inc"
 %include "partition_table.inc"
+%include "fat32/fat32_structures.inc"
 
-; ###############
+ALIGN 4
-; End Section
-; ###############
-
-ALIGN 4, db 0x90
 init:
     cli                             ; We do not want to be interrupted
+    xor ax, ax                      
+    mov ds, ax                      ; Set segment registers to 0x0000
+    mov es, ax
+    mov fs, ax
+    mov gs, ax
 
-    xor ax, ax                  ; 0 AX
+    ;
-    mov ds, ax                  ; Set segment registers to 0
+    ; Zero BSS section
+    mov cx, (end_bss - begin_bss)     ; count = bss length                    
+    mov ax, begin_bss
+    mov di, ax                        ; es:di is dest
+    xor ax, ax
+    cld
+    rep stosb                         ; zero bss section
 
     mov ss, ax                      ; Set Stack Segment to 0
-    mov sp, EARLY_STACK_START   ; Setup stack
+    mov sp, stack_top               ; Setup stack
     mov bp, sp                      ; base ptr = stack ptr
-    sub sp, 0x20                ; local varible space             
+    sub sp, 0x10                    ; local varible space
 
+    xor cx, cx
     mov ch, 0x01                    ; 256 WORDs in MBR (512 bytes), 0x0100 in cx
     mov si, 0x7C00                  ; Current MBR Address (loaded here by BIOS)
     mov di, MBR_ENTRY               ; New MBR Address (our new relocation address)
@@ -69,23 +74,15 @@ init:
     jmp 0:main
 
 ; ###############
-;
 ; Extra/Shared Functions
-;
 ; ###############
 
 %include "util/kmem_func.nasm"
 %include "util/error_func.nasm"
 
-; ###############
-; End Section
-; ###############
-
 ;
 ; bp - 2 : uint8_t boot_drive
 ; bp - 4 : uint16_t part_offset
-;
-
 ALIGN 4, db 0x90
 main:
     mov byte [bp - 2], dl            ; BIOS passes drive number in DL
@@ -130,12 +127,11 @@ main:
         mov dword eax, dword [bx + PartEntry_t.lba_start]
         push dword eax                                     ; lba
 
-        xor ax, ax
-        push ax                                            ; offset = 0
-
         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, 
         ;                         uint32_t lba,
@@ -147,18 +143,19 @@ main:
         je main.sig_ok
         ERROR MBR_ERROR_NO_VBR_SIG                        ; no signature present
     .sig_ok:
-        mov ax, partition_table_SIZE            ; 72 bytes of data
+        mov ax, PartTable_t_size                
         push ax
         mov ax, DiskSig                         ; start of partition table
         push ax
-        mov ax, partition_table                 ; defined in memory.inc
+        mov ax, partition_table                 
         push ax
-        call kmemcpy                            ; copy partition table to memory
+        call kmemcpy                            ; copy partition table to bss
         add sp, 0x6
 
         mov si, word [bp - 4]
         mov dl, byte [bp - 2]
-        jmp 0:0x7C00
+        mov bx, partition_table
+        jmp word 0x0000:0x7C00
 
 ; ###############
 ;
@@ -168,10 +165,6 @@ main:
 
 %include 'BIOS/func/ext_read.nasm'
 
-; ###############
-; End Section
-; ###############
-
 %assign bytes_remaining (440 - ($ - $$))
 %warning MBR has bytes_remaining bytes remaining for code (MAX: 440 bytes)
 times ((512 - 72) - ($ - $$)) nop     ; Fill the rest of sector with nop
@@ -193,3 +186,26 @@ PartEntry4:
     times 16 db 0x00
 BootSig:
     dw 0xAA55                    ; Add boot signature at the end of bootloader
+; this should mark the 512 byte mark...if not, something has gone wrong.
+section .bss follows=.text
+begin_bss:
+
+align 16, resb 1
+partition_table resb PartTable_t_size
+
+align 16, resb 1
+fat32_bpb resb FAT32_bpb_t_size
+fat32_ebpb resb FAT32_ebpb_t_size
+
+align 16, resb 1
+fat32_nc_data resb 16
+
+align 16, resb 1
+lba_packet resb LBAPkt_t_size
+
+align 512, resb 1
+stack_bottom resb 1024                  ; 1Kib stack early on
+
+stack_top:
+mbr_redzone resb 32
+end_bss:

src/stage2/stage2.nasm

@@ -19,27 +19,24 @@
 ; SOFTWARE.
 
 [BITS 16]
-[ORG 0X7E00]
+[ORG 0x0500]                            ; IF YOU CHANGE ORG CHANGE THE SIGN OFFSET AT THE END
 [CPU KATMAI]
 [map all stage2.map]
 [WARNING -reloc-abs-byte]
 [WARNING -reloc-abs-word]
 [WARNING -reloc-abs-dword]              ; Yes, we use absolute addresses. surpress these warnings.
 %define __STEVIA_STAGE2
-
+%define __STAGE2_SEGMENT 0x0000
-
 
 ; ###############
-;
 ; Headers/Includes/Definitions
-;
 ; ###############
 
 %include "util/bochs_magic.inc"
 %include "cdecl16.inc"
 %include "entry.inc"
 %include "config.inc"
-%include "mem.inc"
+%include "early_mem.inc"
 %include "error_codes.inc"
 
 %macro print_string 1
@@ -50,57 +47,130 @@
 %endmacro
 
 section .text
-org 0x7E00
+org 0x0500
+
 begin_text:
 jmp short (init - $$)
 nop
 
+; dl = byte boot_drive
+; si = word part_offset (active partition offset)
+; bx = ptr PartTable_t partition_table
+; dx = ptr FAT32_bpb_t fat32_bpb
 ALIGN 4, db 0x90
 init:
     cli                               ; We do not want to be interrupted
 
-    xor ax, ax                  ; 0 AX
+    ;
-    mov ds, ax                  ; Set segment registers to 0
+    ; Zero BSS section
+    ;
+    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
+    ; done zeroing BSS
+
+    mov ax, __STAGE2_SEGMENT          ; set all our segments to the configured segment
+    mov ds, ax                        ; *
     mov es, ax                        ; *
     mov fs, ax                        ; *
     mov gs, ax                        ; *
 
-    mov ss, ax                        ; Set Stack Segment to 0
+    mov ss, ax                        ; Set Stack Segment to data segment
-    mov sp, EARLY_STACK_START         ; Set Stack Pointer
+    mov sp, stack_top                 ; Set Stack Pointer
+
     mov bp, sp
     sub sp, 0x20                      ; 32 bytes for local varibles
 
     sti
 
-    jmp 0:main
+    jmp word __STAGE2_SEGMENT:main
 
 ; ###############
-;
+; Functions
-; Extra/Shared Functions
-;
 ; ###############
 
 %include "util/kmem_func.nasm"
+%include "util/kmemcpy5_func.nasm"
+%include "util/kmemset4_func.nasm"
 %include "util/error_func.nasm"
 
-; bp - 2 : uint8_t boot_drive
+; ###############
-; bp - 4 : uint16_t part_offset
+; FAT32 Driver
+; ###############
+
+boot_drive_ptr:
+    dw 0x0000
+partition_offset_ptr:
+    dw 0x0000
+
+%include 'fat32/FAT32_SYS.inc'
+
+; ###############
+; BIOS functions
+; ###############
+
+%include 'BIOS/BIOS_SYS.inc'
+
+; structures
+
+struc SteviaInfoStruct_t
+    .MemoryMapPtr      resd 1
+    .MemoryMapEntries  resd 1
+endstruc
+
+struc EarlyBootStruct_t
+    .partition_table resb PartTable_t_size
+    .fat32_bpb       resb FAT32_bpb_t_size
+    .fat32_ebpb      resb FAT32_ebpb_t_size
+endstruc
+
+; bp - 2 : byte boot_drive
+; bp - 4 : word part_offset
+; bp - 6 : ptr PartTable_t partition_table
+; bp - 8 : ptr FAT32_bpb_t fat32_bpb
 ALIGN 4, db 0x90
 main:
     lea ax, [bp - 2]
     mov [boot_drive_ptr], ax
+
     lea ax, [bp - 4]
     mov [partition_offset_ptr], ax      ; setup pointers to boot_drive and partition offset on stack
 
     mov byte [bp - 2], dl               ; boot_drive (probably 0x80)
     mov word [bp - 4], si               ; partition_offset
-
+    mov word [bp - 6], bx               ; partition_table
+    mov word [bp - 8], dx               ; fat32_bpb
+.check_sig:
     mov eax, dword [STAGE2_SIG]
     cmp eax, 0xDEADBEEF
-    je main.signature_present
+    je main.stage2_main
     ERROR STAGE2_SIGNATURE_MISSING
+.stage2_main:
+    mov ax, PartTable_t_size
+    push ax
+    mov ax, [bp - 6]                                    ; ptr partition_table
+    mov ax, partition_table                                  
+    push ax
+    call kmemcpy                                       ; copy partition table data
+    add sp, 0x6
+                                          
+    mov ax, (FAT32_bpb_t_size + FAT32_ebpb_t_size)         ; size in byte
+    push ax
+    mov ax, [bp - 8]                                    ; start of bpb - 0x3 for the jump short main at the start
+    push ax
+    mov ax, fat32_bpb                                  ; defined in memory.inc, destination
+    push ax
+    call kmemcpy                                       ; copy bpb & ebpb to memory
+    add sp, 0x6
 
-.signature_present:
     call SetTextMode
     call disable_cursor
     print_string HelloPrompt_cstr
@@ -121,6 +191,7 @@ main:
     call InitFATDriver
     print_string InitFATSYS_OK_cstr
 
+    ERROR STEVIA_DEBUG_HALT
     ;
     ; Find first cluster of bootable file
     ;
@@ -136,27 +207,6 @@ hcf:
     hlt
     jmp short (hcf - $$)
 
-; ###############
-;
-; FAT32 Driver
-;
-; ###############
-
-boot_drive_ptr:
-    dw 0x0000
-partition_offset_ptr:
-    dw 0x0000
-
-%include 'fat32/FAT32_SYS.inc'
-
-; ###############
-;
-; BIOS functions
-;
-; ###############
-
-%include 'BIOS/BIOS_SYS.inc'
-
 ; ##############################
 ;
 ; SYSTEM CONFIGURATION FUNCTIONS
@@ -280,14 +330,16 @@ EnterUnrealMode:
     push ss
 
     push cs                               ; save real mode code selector
+    xor ax, ax                            ;
     pop ax                                ; save cs to ax to setup far jump
-    mov word [ds:__UNREAL_SEGMENT], ax    
+    mov word [__UNREAL_SEGMENT], ax    
+
+    lgdt [((__STAGE2_SEGMENT << 4) + unreal_gdt_info)]                 ; load unreal gdt
 
-    lgdt [unreal_gdt_info]
     mov eax, cr0                          
     or al,1                               ; set pmode bit
     mov cr0, eax                          ; switch to pmode
-    jmp $+2                               ; clear instruction cache
+    jmp short $+2
 
     ;jmp far 0x0008:EnterUnrealMode.load_cs
     db 0xEA                               ; jmp far imm16:imm16
@@ -304,7 +356,7 @@ EnterUnrealMode:
     
     and al,0xFE                           ; toggle bit 1 of cr0
     mov cr0, eax                          ; back to realmode
-    jmp $+2                     ; clear instruction cache again
+    jmp short $+2
     
     ;jmp far 0x0008:EnterUnrealMode.unload_cs
     db 0xEA                               ; jmp far imm16:imm16
@@ -367,58 +419,33 @@ IntToHex_table:
     db '0123456789ABCDEF'
 
 ; see docs/gdt.txt for a quick refresher on GDT 
-ALIGN 4, db 0
+ALIGN 16, db 0
 unreal_gdt_info:
     unreal_gdt_size: dw (unreal_gdt_end - unreal_gdt_start) - 1
-    unreal_gdt_ptr:  dd unreal_gdt_start
+    unreal_gdt_ptr:  dd ((__STAGE2_SEGMENT << 4) + unreal_gdt_start)
-
 unreal_gdt_start:
-    ; entry 0
+    ; entry 0 (null descriptor)
     dq 0                    ; first entry is null
 
-    ; entry 1 (4 GiB flat code map)
+    ; entry 1 (16bit code 64KiB limit)
-    dw 0xFFFF            ; Segment Limit 15:0 (Same large limit as data segment)
+    dd 0x0000FFFF        ; Base Address(15:0) 31:16, Segment Limit(15:0) 15:0
-    dw 0x0000            ; Base Address 15:0
     db 0x00              ; Base Address 23:16
-    db 1001_1010b        ; Access Byte: 1001_1010b for executable code
+    db 1001_1010b        ; Access Byte: Present, ring0, S = 1, executable (1), non-conforming, readable, Accessed
-    db 1000_1111b        ; Flags and Segment Limit 19:16 (Same as data segment)
+    db 0000_0000b        ; Flags: GR = 4KiB, attr = <DB/L/Avl>, Granularity = 4KiB & 16:19 of limit
     db 0x00              ; Base Address 31:24
 
-    ; entry 2 (4 GiB flat data map)
+    ; entry 2 (16bit data segment with 4 GiB flat mapping)
-    dw 0xFFFF               ; 0:15 limit
+    dd 0x0000FFFF        ; Base Address(15:0) 31:16, Segment Limit(15:0) 15:0
-    dw 0x0000               ; 0:15 base
+    db 0x00              ; Base Address(23:16)
-    db 0x00                 ; 16:23 base
+    db 1001_0010b        ; Access Byte: Present, ring0, S = 1, data (0), non-confirming, writable, present
-    db 1001_0010b            ; bit 0:4 = S/Type, [1, DC, RW, Ac] <code> or [0, E, RW, Ac] <data>
+    db 1000_1111b        ; Flags: GR = 4KiB, attr = <16-bit/?/?>, Granularity = 4KiB & 16:19 of limit
-                            ; bit 5:6 = Privl
+    db 0x00              ; Base Address(31:24)
-                            ; bit 7   = Present
-
-    db 1000_1111b            ; bit 0:3 = 16:19 of Limit
-                            ; bit 4 = Availible to software bit
-                            ; bit 5 = Reserved (?)
-                            ; bit 6 = D/B bit, depending on if this is code/data 1 = 32 bit operands or stack size
-                            ; bit 7 = Granularity bit. 1 = multiply limit by 4096
-    db 0x00                 ; base 24:31
-    ; at the end of the day...
-    ; base = 0x00000000
-    ; limit = 0xFFFFF
-    ; Accessed = 0, ignore this field
-    ; RW = 1, data is Read/Write
-    ; E = 0, Expand up, valid data is from base -> limit, if 1 valid data is from (limit + 1) -> base
-    ; C/D = 0, Segment is a data segment
-    ; S = 1, Segment is a system segment
-    ; Privl = 00b, Ring0 segment
-    ; Pr = 1, segment is present
-    ; AVL = 0, ignore this field
-    ; D/B bit = 0, 16bit code/stack
-    ; Gr = 1, multiply limit by 4096 
 unreal_gdt_end:
 
-ALIGN 4, db 0
+ALIGN 16, db 0
 gdt32_info:
     gdt32_size: dw (gdt32_end - gdt32_start) - 1
-    gdt32_ptr:  dd gdt32_start
+    gdt32_ptr:  dd ((__STAGE2_SEGMENT << 4) + gdt32_start)
-
-; check above for detailed information
 gdt32_start:
     dq 0
     .gdt32_code:
@@ -465,15 +492,58 @@ end_data:
 
 ; section start location needs to be a 'critical expression'
 ; 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
 
 section .bss follows=.sign
-align 512
+align 512, resb 1
 begin_bss:
-buffer1 resb 512
+stack_bottom:
-buffer2 resb 512
+    resb 4096
-buffer3 resb 512
+stack_top:
-buffer4 resb 512
+stage2_main_redzone:
+    resb 32
+
+align 16, resb 1
+partition_table resb PartTable_t_size
+
+align 16, resb 1
+fat32_bpb resb FAT32_bpb_t_size
+fat32_ebpb resb FAT32_ebpb_t_size
+
+align 16, resb 1
+fat32_nc_data resb 16
+
+align 16, resb 1
+lba_packet resb LBAPkt_t_size
+
+align 16, resb 1
+SteviaInfo:
+    resd 4
+align 16, resb 1
+fat32_state:
+    resb FAT32_State_t_size
+
+align 16, resb 1
+mbr_sector_data:
+    resb 512
+vbr_sector_data:
+    resb 512
+
+align 16, resb 1
+disk_buffer:
+    resb 512
+fat_buffer:
+    resb 512
+dir_buffer:
+    resb 512
+fat_fsinfo:
+    resb 512
+
+align 16, resb 1
+%define BIOSMemoryMap_SIZE 2048
+BIOSMemoryMap:
+    resb 2048
+
 end_bss:

src/vbr/vbr.nasm

@@ -24,12 +24,11 @@
 [WARNING -reloc-abs-word]
 [map all vbr.map]                   ; Yes, we use absolute addresses. surpress these warnings.
 %define __STEVIA_VBR
-
+section .text
 __ENTRY:
     jmp short (init - $$)
     nop
 
-phy_bpb_start:
 ; fill BPB area with 0x00 since we skip writing this part to disk
 ; but we need it for the 'jmp short entry; nop' above
 times 33 db 0x00
@@ -47,35 +46,43 @@ times 54 db 0x00
 %include "cdecl16.inc"
 %include "entry.inc"
 %include "config.inc"
-%include "mem.inc"
+%include "early_mem.inc"
 %include "error_codes.inc"
+%include "partition_table.inc"
+%include "fat32/fat32_structures.inc"
 %include "fat32/bpb_offset_bx.inc"
-
+;
-; ###############
+; dl = boot_drive
-; End Section
+; si = part_offset
-; ###############
+; bx = partition_table location from mbr
-
+ALIGN 4
-ALIGN 4, db 0x90
 init:
     cli                             ; We do not want to be interrupted
+    xor ax, ax                      
+    mov ds, ax                      ; Set segment registers to 0x0000
+    mov es, ax
 
-    xor ax, ax                  ; 0 AX
+    ; zero bss section
-    mov ds, ax                  ; Set segment registers to 0
+    mov cx, (end_bss - begin_bss)     ; count = bss length                    
+    mov ax, begin_bss
+    mov di, ax                        ; es:di is dest
+    xor ax, ax
+    cld
+    rep stosb                         
 
+    xor ax, ax
     mov ss, ax                      ; Set Stack Segment to 0
-    mov sp, EARLY_STACK_START   ; Setup stack
+    mov sp, stack_top               ; Setup stack
     mov bp, sp                      ; base ptr = stack ptr
-    sub sp, 0x20                ; local varible space
+    sub sp, 0x10                    ; local varible space
 
-    mov bx, VBR_ENTRY           ; move Bx to the new start of the initial boot sector
+    mov cx, bx                      ; mov partition_table locaiton to cx
     sti                             ; all done with inital setup and relocation, reenable interupts
 
     jmp 0:main                      ; fix up cs:ip just in case and jump to relocated code
 
 ; ###############
-;
 ; Extra/Shared Functions
-;
 ; ###############
 
 %include "util/kmem_func.nasm"
@@ -85,27 +92,41 @@ init:
 ; End Section
 ; ###############
 
+;
+; byte boot_drive @ bp - 2
+; word part_offset @ bp - 4
+; ptr partition_table
 ALIGN 4, db 0x90
 main:
     mov byte [bp - 2], dl                 ; boot_drive
-    mov [bp - 4], si                 ; part_offset
+    mov word [bp - 4], si                 ; part_offset
+    mov word [bp - 6], cx                 ; partition_table
 
+.load_fs_data:
+    mov ax, PartTable_t_size
+    push ax
+    mov ax, [bp - 6]                                    ; ptr partition_table
+    mov ax, partition_table                                  
+    push ax
+    call kmemcpy                                       ; copy partition table data
+    add sp, 0x6
+                                          
+    mov ax, (FAT32_bpb_t_size + FAT32_ebpb_t_size)     ; size in byte
+    push ax
+    mov ax, __ENTRY                                    
+    push ax
+    mov ax, fat32_bpb                                  ; 
+    push ax
+    call kmemcpy                                       ; copy bpb & ebpb to memory
+    add sp, 0x6
+
+    mov bx, fat32_bpb                                  ; bx now points to aligned memory structure
 .check_FAT_size:                     ; we only support a very specific setup of FAT32
     cmp dword [bsSectorHuge], 0      ; SectorsHuge will not be set if FAT12/16
     ja main.load_stage2
     ERROR VBR_ERROR_WRONG_FAT_SIZE
-.load_stage2:                                          ; read sectors 1-63 to stage2 entry point
+.load_stage2:
-    mov ax, (fat32_bpb_SIZE + fat32_ebpb_SIZE)         ; size in byte
+    ; read sectors 1-(MAX_STAGE2_BYTES / 512) to stage2 entry point
-    push ax
-    mov ax, (phy_bpb_start - 0x3)                      ; start of bpb - 0x3 for the jump short main at the start
-    push ax
-    mov ax, fat32_bpb                                  ; defined in memory.inc, destination
-    push ax
-    call kmemcpy                                       ; copy bpb to memory
-    add sp, 0x6
-
-    mov bx, fat32_bpb                                  ; bx now points to aligned memory structure
-
     movzx ax, byte [bp - 2]
     push ax                                            ; drive_num
 
@@ -115,32 +136,23 @@ main:
     mov dword eax, 0x1
     push dword eax                                     ; lba
 
-    xor ax, ax
-    push ax                                            ; offset = 0
-
-    ; 07E0:0 = 0x00007e00
     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, 
     ;                         uint32_t lba,
     ;                         uint16_t count, uint16_t drive_num)
     call read_disk_raw
     add sp, 0xC
-
+.enter_stage2:
-.check_sig:
+    mov dl, byte [bp - 2]               ; boot_drive
-    mov ax, 0x7E0
+    mov si, word [bp - 4]               ; part_offset
-    mov fs, ax
+    mov bx, partition_table
-    cmp dword [fs:0x7FFC], 0xDEADBEEF
+    mov dx, fat32_bpb
-    je main.sig_ok
+    jmp word 0x0000:STAGE2_ENTRY
-
-    ERROR VBR_ERROR_NO_SIGNATURE          ; no signature present in stage2
-    
-.sig_ok:
-    mov si, word [bp - 4]
-    mov dl, byte [bp - 2]
-    jmp 0:0x7E00
 
 ; ###############
 ; Required BIOS function(s)
@@ -155,3 +167,26 @@ times (510 - ($ - $$)) nop     ; Fill the rest of sector with nop
 
 BootSig:
     dw 0xAA55                    ; Add boot signature at the end of bootloader
+
+section .bss follows=.text
+begin_bss:
+
+align 16, resb 1
+partition_table resb PartTable_t_size
+
+align 16, resb 1
+fat32_bpb resb FAT32_bpb_t_size
+fat32_ebpb resb FAT32_ebpb_t_size
+
+align 16, resb 1
+fat32_nc_data resb 16
+
+align 16, resb 1
+lba_packet resb LBAPkt_t_size
+
+align 512, resb 1
+stack_bottom resb 1024                  ; 1Kib stack early on
+
+stack_top:
+vbr_redzone resb 32
+end_bss: