Hello all, here I am again with something that I can't quite figure out.
I'm starting my barebones kernel over again, in an attempt to get things working right with a proper toolchain. I'm attempting to build the "bare bones" tutorial version of the kernel just to get everything working before I start porting old code over. Trouble is, I can't seem to find any proper documentation on the FASM assembler syntax, and/or I'm not sure how to perform the conversion from the given NASM and GAS syntax files. I understand what the files are supposed to do, but I don't understand how to represent those files in FASM syntax.
Could someone point me toward a resource that would help me understand how to actually port this code over? The main reason I ask is that, although I personally have nothing against any particular assembler, all the folks here who have provided help so far have done so using FASM code, and I feel that it is the standard that should be used. I'd like to get my kernel's loader compiling with FASM and linking in with my C code, but I can't even tell from the documentation if FASM supports that kind of operation. Can someone shed some light on the subject? Thanks.
A very confused beginner,
-Nick
Starting Out with FASM
Re: Starting Out with FASM
Fasm and nasm are very much alike with just small differancs
Example, here the bootload bootprog written in nasm
Here it is converted to fasm
Example, here the bootload bootprog written in nasm
Code: Select all
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; ;;
;; "BootProg" Loader v 1.2 by Alexei A. Frounze (c) 2000 ;;
;; ;;
;; ;;
;; Contact Information: ;;
;; ~~~~~~~~~~~~~~~~~~~~ ;;
;; E-Mail: [email protected] ;;
;; Homepage: http://alexfru.chat.ru ;;
;; Mirror: http://members.xoom.com/alexfru ;;
;; ;;
;; ;;
;; Thanks: ;;
;; ~~~~~~~ ;;
;; Thanks Thomas Kjoernes (aka NowhereMan) for his excelent idea ;;
;; ;;
;; ;;
;; Features: ;;
;; ~~~~~~~~~ ;;
;; - FAT12 supported ;;
;; ;;
;; - Loads particular COM or EXE file placed to the root directory of a disk;;
;; ("ProgramName" variable holds name of a file to be loaded) ;;
;; ;;
;; - Provides simple information about errors occured during load process ;;
;; ("RE" message stands for "Read Error", ;;
;; "NF" message stands for "file Not Found") ;;
;; ;;
;; ;;
;; Known Limitations: ;;
;; ~~~~~~~~~~~~~~~~~~ ;;
;; - Works only on the 1st MBR partition which must be a PRI DOS partition ;;
;; with FAT12 (File System ID: 1) ;;
;; ;;
;; ;;
;; Known Bugs: ;;
;; ~~~~~~~~~~~ ;;
;; - All bugs are fixed as far as I know. The boot sector tested on the ;;
;; following types of diskettes: 360KB 5"25, 1.2MB 5"25, 1.44MB 3"5. ;;
;; ;;
;; ;;
;; Memory Map: ;;
;; ~~~~~~~~~~~ ;;
;; ������������Ŀ ;;
;; Interrupt Vector Table 0000 ;;
;; ������������Ĵ ;;
;; BIOS Data Area 0040 ;;
;; ������������Ĵ ;;
;; PrtScr Status / Unused 0050 ;;
;; ������������Ĵ ;;
;; Image Load Address 0060 ;;
;; ������������Ĵ ;;
;; Available Memory nnnn ;;
;; ������������Ĵ ;;
;; 2KB Boot Stack A000 - 512 - 2KB ;;
;; ������������Ĵ ;;
;; Boot Sector A000 - 512 ;;
;; ������������Ĵ ;;
;; A000 ;;
;; ;;
;; ;;
;; Boot Image Startup (register values): ;;
;; ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ;;
;; dl = boot drive number ;;
;; cs:ip = program entry point ;;
;; ss:sp = program stack (don't confuse with boot sector's stack) ;;
;; COM program defaults: cs = ds = es = ss = 50h, sp = 0, ip = 100h ;;
;; EXE program defaults: ds = es = 50h, other stuff depends on EXE header ;;
;; ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
[BITS 16]
? equ 0
ImageLoadSeg equ 60h
[SECTION .text]
[ORG 0]
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Boot sector starts here ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
jmp short start
nop
bsOemName DB "BootProg" ; 0x03
;;;;;;;;;;;;;;;;;;;;;
;; BPB starts here ;;
;;;;;;;;;;;;;;;;;;;;;
bpbBytesPerSector DW ? ; 0x0B
bpbSectorsPerCluster DB ? ; 0x0D
bpbReservedSectors DW ? ; 0x0E
bpbNumberOfFATs DB ? ; 0x10
bpbRootEntries DW ? ; 0x11
bpbTotalSectors DW ? ; 0x13
bpbMedia DB ? ; 0x15
bpbSectorsPerFAT DW ? ; 0x16
bpbSectorsPerTrack DW ? ; 0x18
bpbHeadsPerCylinder DW ? ; 0x1A
bpbHiddenSectors DD ? ; 0x1C
bpbTotalSectorsBig DD ? ; 0x20
;;;;;;;;;;;;;;;;;;;
;; BPB ends here ;;
;;;;;;;;;;;;;;;;;;;
bsDriveNumber DB ? ; 0x24
bsUnused DB ? ; 0x25
bsExtBootSignature DB ? ; 0x26
bsSerialNumber DD ? ; 0x27
bsVolumeLabel DB "NO NAME " ; 0x2B
bsFileSystem DB "FAT12 " ; 0x36
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Boot sector code starts here ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
start:
cld
;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; How much RAM is there? ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;
int 12h ; get conventional memory size (in KBs)
shl ax, 6 ; and convert it to paragraphs
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Reserve some memory for the boot sector and the stack ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
sub ax, 512 / 16 ; reserve 512 bytes for the boot sector code
mov es, ax ; es:0 -> top - 512
sub ax, 2048 / 16 ; reserve 2048 bytes for the stack
mov ss, ax ; ss:0 -> top - 512 - 2048
mov sp, 2048 ; 2048 bytes for the stack
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Copy ourself to top of memory ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
mov cx, 256
mov si, 7C00h
xor di, di
mov ds, di
rep movsw
;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Jump to relocated code ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;
push es
push word main
retf
main:
push cs
pop ds
mov [bsDriveNumber], dl ; store boot drive number
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Reserve some memory for a FAT12 image (6KB max) and load it whole ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
mov ax, [bpbBytesPerSector]
shr ax, 4 ; ax = sector size in paragraphs
mov cx, [bpbSectorsPerFAT] ; cx = FAT size in sectors
mul cx ; ax = FAT size in paragraphs
mov di, ss
sub di, ax
mov es, di
xor bx, bx ; es:bx -> buffer for the FAT
mov ax, [bpbHiddenSectors]
mov dx, [bpbHiddenSectors+2]
add ax, [bpbReservedSectors]
adc dx, bx ; dx:ax = LBA
call ReadSector
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Reserve some memory for a root directory and load it whole ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
mov bx, ax
mov di, dx ; save LBA to di:bx
mov ax, 32
mov si, [bpbRootEntries]
mul si
div word [bpbBytesPerSector]
mov cx, ax ; cx = root directory size in sectors
mov al, [bpbNumberOfFATs]
cbw
mul word [bpbSectorsPerFAT]
add ax, bx
adc dx, di ; dx:ax = LBA
push es ; push FAT segment (2nd parameter)
push word ImageLoadSeg
pop es
xor bx, bx ; es:bx -> buffer for root directory
call ReadSector
add ax, cx
adc dx, bx ; adjust LBA for cluster data
push dx
push ax ; push LBA for data (1st parameter)
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Look for a COM/EXE program to be load and run ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
mov di, bx ; es:di -> root entries array
mov dx, si ; dx = number of root entries
mov si, ProgramName ; ds:si -> program name
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Looks for a file with particular name ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Input: DS:SI -> file name (11 chars) ;;
;; ES:DI -> root directory array ;;
;; DX = number of root entries ;;
;; Output: SI = cluster number ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
FindName:
mov cx, 11
FindNameCycle:
cmp byte [es:di], ch
je FindNameFailed ; end of root directory
pusha
repe cmpsb
popa
je FindNameFound
add di, 32
dec dx
jnz FindNameCycle ; next root entry
FindNameFailed:
jmp ErrFind
FindNameFound:
mov si, [es:di+1Ah] ; si = cluster no.
;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Load entire a program ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;
ReadNextCluster:
call ReadCluster
cmp si, 0FF8h
jc ReadNextCluster ; if not End Of File
;;;;;;;;;;;;;;;;;;;
;; Type checking ;;
;;;;;;;;;;;;;;;;;;;
cli ; for stack adjustments
mov ax, ImageLoadSeg
mov es, ax
cmp word [es:0], 5A4Dh ; "MZ" signature?
je RelocateEXE ; yes, it's an EXE program
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Setup and Run COM program ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
mov ax, es
sub ax, 10h ; "org 100h" stuff :)
mov es, ax
mov ds, ax
mov ss, ax
xor sp, sp
push es
push word 100h
jmp Run
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Relocate, setup and run EXE program ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
RelocateEXE:
mov ds, ax
add ax, [ds:08h] ; ax = image base
mov cx, [ds:06h] ; cx = reloc items
mov bx, [ds:18h] ; bx = reloc table pointer
jcxz RelocationDone
ReloCycle:
mov di, [ds:bx] ; di = item ofs
mov dx, [ds:bx+2] ; dx = item seg (rel)
add dx, ax ; dx = item seg (abs)
push ds
mov ds, dx ; ds = dx
add [ds:di], ax ; fixup
pop ds
add bx, 4 ; point to next entry
loop ReloCycle
RelocationDone:
mov bx, ax
add bx, [ds:0Eh]
mov ss, bx ; ss for EXE
mov sp, [ds:10h] ; sp for EXE
add ax, [ds:16h] ; cs
push ax
push word [ds:14h] ; ip
Run:
mov dl, [cs:bsDriveNumber] ; let program know boot drive
sti
retf
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Reads a FAT12 cluster ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Inout: ES:BX -> buffer ;;
;; SI = cluster no ;;
;; Output: SI = next cluster ;;
;; ES:BX -> next addr ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
ReadCluster:
mov bp, sp
lea ax, [si-2]
xor ch, ch
mov cl, [bpbSectorsPerCluster]
; cx = sector count
mul cx
add ax, [ss:bp+1*2]
adc dx, [ss:bp+2*2]
; dx:ax = LBA
call ReadSector
mov ax, [bpbBytesPerSector]
shr ax, 4 ; ax = paragraphs per sector
mul cx ; ax = paragraphs read
mov cx, es
add cx, ax
mov es, cx ; es:bx updated
mov ax, 3
mul si
shr ax, 1
xchg ax, si ; si = cluster * 3 / 2
push ds
mov ds, [ss:bp+3*2] ; ds = FAT segment
mov si, [ds:si] ; si = next cluster
pop ds
jnc ReadClusterEven
shr si, 4
ReadClusterEven:
and si, 0FFFh ; mask cluster value
ReadClusterDone:
ret
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Reads a sector using BIOS Int 13h fn 2 ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Input: DX:AX = LBA ;;
;; CX = sector count ;;
;; ES:BX -> buffer address ;;
;; Output: CF = 1 if error ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
ReadSector:
pusha
ReadSectorNext:
mov di, 5 ; attempts to read
ReadSectorRetry:
pusha
div word [bpbSectorsPerTrack]
; ax = LBA / SPT
; dx = LBA % SPT = sector - 1
mov cx, dx
inc cx
; cx = sector no.
xor dx, dx
div word [bpbHeadsPerCylinder]
; ax = (LBA / SPT) / HPC = cylinder
; dx = (LBA / SPT) % HPC = head
mov ch, al
; ch = LSB 0...7 of cylinder no.
shl ah, 6
or cl, ah
; cl = MSB 8...9 of cylinder no. + sector no.
mov dh, dl
; dh = head no.
mov dl, [bsDriveNumber]
; dl = drive no.
mov ax, 201h
; al = sector count
; ah = 2 = read function no.
int 13h ; read sectors
jnc ReadSectorDone ; CF = 0 if no error
xor ah, ah ; ah = 0 = reset function
int 13h ; reset drive
popa
dec di
jnz ReadSectorRetry ; extra attempt
jmp short ErrRead
ReadSectorDone:
popa
dec cx
jz ReadSectorDone2 ; last sector
add bx, [bpbBytesPerSector] ; adjust offset for next sector
add ax, 1
adc dx, 0 ; adjust LBA for next sector
jmp short ReadSectorNext
ReadSectorDone2:
popa
ret
;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Error Messaging Code ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;
ErrRead:
mov si, MsgErrRead
jmp short Error
ErrFind:
mov si, MsgErrFind
Error:
mov ah, 0Eh
mov bx, 7
lodsb
int 10h ; 1st char
lodsb
int 10h ; 2nd char
jmp short $ ; hang
;;;;;;;;;;;;;;;;;;;;;;
;; String constants ;;
;;;;;;;;;;;;;;;;;;;;;;
MsgErrRead db "RE"
MsgErrFind db "NF"
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Fill free space with zeroes ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
times (512-13-($-$$)) db 0
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Name of a program to be load and run ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
ProgramName db "STARTUP BIN" ; name and extension must be padded
; with spaces (11 bytes total)
;;;;;;;;;;;;;;;;;;;;;;;;;;
;; End of the sector ID ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;
dw 0AA55h
Code: Select all
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; ;;
;; "BootProg" Loader v 1.2 by Alexei A. Frounze (c) 2000 ;;
;; ;;
;; ;;
;; Contact Information: ;;
;; ~~~~~~~~~~~~~~~~~~~~ ;;
;; E-Mail: [email protected] ;;
;; Homepage: http://alexfru.chat.ru ;;
;; Mirror: http://members.xoom.com/alexfru ;;
;; ;;
;; ;;
;; Thanks: ;;
;; ~~~~~~~ ;;
;; Thanks Thomas Kjoernes (aka NowhereMan) for his excelent idea ;;
;; ;;
;; ;;
;; Features: ;;
;; ~~~~~~~~~ ;;
;; - FAT12 supported ;;
;; ;;
;; - Loads particular COM or EXE file placed to the root directory of a disk;;
;; ("ProgramName" variable holds name of a file to be loaded) ;;
;; ;;
;; - Provides simple information about errors occured during load process ;;
;; ("RE" message stands for "Read Error", ;;
;; "NF" message stands for "file Not Found") ;;
;; ;;
;; ;;
;; Known Limitations: ;;
;; ~~~~~~~~~~~~~~~~~~ ;;
;; - Works only on the 1st MBR partition which must be a PRI DOS partition ;;
;; with FAT12 (File System ID: 1) ;;
;; ;;
;; ;;
;; Known Bugs: ;;
;; ~~~~~~~~~~~ ;;
;; - All bugs are fixed as far as I know. The boot sector tested on the ;;
;; following types of diskettes: 360KB 5"25, 1.2MB 5"25, 1.44MB 3"5. ;;
;; ;;
;; ;;
;; Memory Map: ;;
;; ~~~~~~~~~~~ ;;
;; ������������Ŀ ;;
;; Interrupt Vector Table 0000 ;;
;; ������������Ĵ ;;
;; BIOS Data Area 0040 ;;
;; ������������Ĵ ;;
;; PrtScr Status / Unused 0050 ;;
;; ������������Ĵ ;;
;; Image Load Address 0060 ;;
;; ������������Ĵ ;;
;; Available Memory nnnn ;;
;; ������������Ĵ ;;
;; 2KB Boot Stack A000 - 512 - 2KB ;;
;; ������������Ĵ ;;
;; Boot Sector A000 - 512 ;;
;; ������������Ĵ ;;
;; A000 ;;
;; ;;
;; ;;
;; Boot Image Startup (register values): ;;
;; ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ;;
;; dl = boot drive number ;;
;; cs:ip = program entry point ;;
;; ss:sp = program stack (don't confuse with boot sector's stack) ;;
;; COM program defaults: cs = ds = es = ss = 50h, sp = 0, ip = 100h ;;
;; EXE program defaults: ds = es = 50h, other stuff depends on EXE header ;;
;; ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
use16
? equ 0
ImageLoadSeg equ 60h
ORG 0
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Boot sector starts here ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
jmp start
nop
bsOemName DB "BootProg" ; 0x03
;;;;;;;;;;;;;;;;;;;;;
;; BPB starts here ;;
;;;;;;;;;;;;;;;;;;;;;
bpbBytesPerSector DW ? ; 0x0B
bpbSectorsPerCluster DB ? ; 0x0D
bpbReservedSectors DW ? ; 0x0E
bpbNumberOfFATs DB ? ; 0x10
bpbRootEntries DW ? ; 0x11
bpbTotalSectors DW ? ; 0x13
bpbMedia DB ? ; 0x15
bpbSectorsPerFAT DW ? ; 0x16
bpbSectorsPerTrack DW ? ; 0x18
bpbHeadsPerCylinder DW ? ; 0x1A
bpbHiddenSectors DD ? ; 0x1C
bpbTotalSectorsBig DD ? ; 0x20
;;;;;;;;;;;;;;;;;;;
;; BPB ends here ;;
;;;;;;;;;;;;;;;;;;;
bsDriveNumber DB ? ; 0x24
bsUnused DB ? ; 0x25
bsExtBootSignature DB ? ; 0x26
bsSerialNumber DD ? ; 0x27
bsVolumeLabel DB "NO NAME " ; 0x2B
bsFileSystem DB "FAT12 " ; 0x36
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Boot sector code starts here ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
start:
cld
;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; How much RAM is there? ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;
int 12h ; get conventional memory size (in KBs)
shl ax, 6 ; and convert it to paragraphs
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Reserve some memory for the boot sector and the stack ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
sub ax, 512 / 16 ; reserve 512 bytes for the boot sector code
mov es, ax ; es:0 -> top - 512
sub ax, 2048 / 16 ; reserve 2048 bytes for the stack
mov ss, ax ; ss:0 -> top - 512 - 2048
mov sp, 2048 ; 2048 bytes for the stack
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Copy ourself to top of memory ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
mov cx, 256
mov si, 7C00h
xor di, di
mov ds, di
rep movsw
;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Jump to relocated code ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;
push es
push word main
retf
main:
push cs
pop ds
mov [bsDriveNumber], dl ; store boot drive number
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Reserve some memory for a FAT12 image (6KB max) and load it whole ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
mov ax, [bpbBytesPerSector]
shr ax, 4 ; ax = sector size in paragraphs
mov cx, [bpbSectorsPerFAT] ; cx = FAT size in sectors
mul cx ; ax = FAT size in paragraphs
mov di, ss
sub di, ax
mov es, di
xor bx, bx ; es:bx -> buffer for the FAT
mov eax, [bpbHiddenSectors]
mov edx, [bpbHiddenSectors+2]
add ax, [bpbReservedSectors]
adc dx, bx ; dx:ax = LBA
call ReadSector
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Reserve some memory for a root directory and load it whole ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
mov bx, ax
mov di, dx ; save LBA to di:bx
mov ax, 32
mov si, [bpbRootEntries]
mul si
div word [bpbBytesPerSector]
mov cx, ax ; cx = root directory size in sectors
mov al, [bpbNumberOfFATs]
cbw
mul word [bpbSectorsPerFAT]
add ax, bx
adc dx, di ; dx:ax = LBA
push es ; push FAT segment (2nd parameter)
push word ImageLoadSeg
pop es
xor bx, bx ; es:bx -> buffer for root directory
call ReadSector
add ax, cx
adc dx, bx ; adjust LBA for cluster data
push dx
push ax ; push LBA for data (1st parameter)
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Look for a COM/EXE program to be load and run ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
mov di, bx ; es:di -> root entries array
mov dx, si ; dx = number of root entries
mov si, ProgramName ; ds:si -> program name
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Looks for a file with particular name ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Input: DS:SI -> file name (11 chars) ;;
;; ES:DI -> root directory array ;;
;; DX = number of root entries ;;
;; Output: SI = cluster number ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
FindName:
mov cx, 11
FindNameCycle:
cmp byte [es:di], ch
je FindNameFailed ; end of root directory
pusha
repe cmpsb
popa
je FindNameFound
add di, 32
dec dx
jnz FindNameCycle ; next root entry
FindNameFailed:
jmp ErrFind
FindNameFound:
mov si, [es:di+1Ah] ; si = cluster no.
;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Load entire a program ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;
ReadNextCluster:
call ReadCluster
cmp si, 0FF8h
jc ReadNextCluster ; if not End Of File
;;;;;;;;;;;;;;;;;;;
;; Type checking ;;
;;;;;;;;;;;;;;;;;;;
cli ; for stack adjustments
mov ax, ImageLoadSeg
mov es, ax
cmp word [es:0], 5A4Dh ; "MZ" signature?
je RelocateEXE ; yes, it's an EXE program
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Setup and Run COM program ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
mov ax, es
sub ax, 10h ; "org 100h" stuff :)
mov es, ax
mov ds, ax
mov ss, ax
xor sp, sp
push es
push word 100h
jmp Run
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Relocate, setup and run EXE program ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
RelocateEXE:
mov ds, ax
add ax, [ds:08h] ; ax = image base
mov cx, [ds:06h] ; cx = reloc items
mov bx, [ds:18h] ; bx = reloc table pointer
jcxz RelocationDone
ReloCycle:
mov di, [ds:bx] ; di = item ofs
mov dx, [ds:bx+2] ; dx = item seg (rel)
add dx, ax ; dx = item seg (abs)
push ds
mov ds, dx ; ds = dx
add [ds:di], ax ; fixup
pop ds
add bx, 4 ; point to next entry
loop ReloCycle
RelocationDone:
mov bx, ax
add bx, [ds:0Eh]
mov ss, bx ; ss for EXE
mov sp, [ds:10h] ; sp for EXE
add ax, [ds:16h] ; cs
push ax
push word [ds:14h] ; ip
Run:
mov dl, [cs:bsDriveNumber] ; let program know boot drive
sti
retf
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Reads a FAT12 cluster ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Inout: ES:BX -> buffer ;;
;; SI = cluster no ;;
;; Output: SI = next cluster ;;
;; ES:BX -> next addr ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
ReadCluster:
mov bp, sp
lea ax, [si-2]
xor ch, ch
mov cl, [bpbSectorsPerCluster]
; cx = sector count
mul cx
add ax, [ss:bp+1*2]
adc dx, [ss:bp+2*2]
; dx:ax = LBA
call ReadSector
mov ax, [bpbBytesPerSector]
shr ax, 4 ; ax = paragraphs per sector
mul cx ; ax = paragraphs read
mov cx, es
add cx, ax
mov es, cx ; es:bx updated
mov ax, 3
mul si
shr ax, 1
xchg ax, si ; si = cluster * 3 / 2
push ds
mov ds, [ss:bp+3*2] ; ds = FAT segment
mov si, [ds:si] ; si = next cluster
pop ds
jnc ReadClusterEven
shr si, 4
ReadClusterEven:
and si, 0FFFh ; mask cluster value
ReadClusterDone:
ret
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Reads a sector using BIOS Int 13h fn 2 ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Input: DX:AX = LBA ;;
;; CX = sector count ;;
;; ES:BX -> buffer address ;;
;; Output: CF = 1 if error ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
ReadSector:
pusha
ReadSectorNext:
mov di, 5 ; attempts to read
ReadSectorRetry:
pusha
div word [bpbSectorsPerTrack]
; ax = LBA / SPT
; dx = LBA % SPT = sector - 1
mov cx, dx
inc cx
; cx = sector no.
xor dx, dx
div word [bpbHeadsPerCylinder]
; ax = (LBA / SPT) / HPC = cylinder
; dx = (LBA / SPT) % HPC = head
mov ch, al
; ch = LSB 0...7 of cylinder no.
shl ah, 6
or cl, ah
; cl = MSB 8...9 of cylinder no. + sector no.
mov dh, dl
; dh = head no.
mov dl, [bsDriveNumber]
; dl = drive no.
mov ax, 201h
; al = sector count
; ah = 2 = read function no.
int 13h ; read sectors
jnc ReadSectorDone ; CF = 0 if no error
xor ah, ah ; ah = 0 = reset function
int 13h ; reset drive
popa
dec di
jnz ReadSectorRetry ; extra attempt
jmp ErrRead
ReadSectorDone:
popa
dec cx
jz ReadSectorDone2 ; last sector
add bx, [bpbBytesPerSector] ; adjust offset for next sector
add ax, 1
adc dx, 0 ; adjust LBA for next sector
jmp ReadSectorNext
ReadSectorDone2:
popa
ret
;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Error Messaging Code ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;
ErrRead:
mov si, MsgErrRead
jmp Error
ErrFind:
mov si, MsgErrFind
Error:
mov ah, 0Eh
mov bx, 7
lodsb
int 10h ; 1st char
lodsb
int 10h ; 2nd char
jmp $ ; hang
;;;;;;;;;;;;;;;;;;;;;;
;; String constants ;;
;;;;;;;;;;;;;;;;;;;;;;
MsgErrRead db "RE"
MsgErrFind db "NF"
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Name of a program to be load and run ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
ProgramName db "KERNEL32EXE" ; name and extension must be padded
; with spaces (11 bytes total)
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Fill free space with zeroes ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
times 510- ($-0) db 0
;;;;;;;;;;;;;;;;;;;;;;;;;;
;; End of the sector ID ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;
dw 0xaa55
Re: Starting Out with FASM
Post the stuff you are having trouble with and I'm sure someone will be able to help you out with it. Other than that, the official manual from the website should have everything you need.
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thegamefreak0134
- Posts: 14
- Joined: Thu Jan 08, 2009 1:54 am
Re: Starting Out with FASM
Thanks to this example, I think I can port over most of my NASM format code. However, and I searched the official docs for this too, how do I link it with C code? Namely, how do I call C functions from assembly using FASM syntax, and how to I expose assembly routines so that C can call assembly functions if needed? I would do this in NASM using global and extern respectively, but I can't seem to find the equivalent statements for FASM.
Also, I noticed that the FASM example that you gave (which is amazing, btw, thanks a bunch for that) doesn't specify the sections. Is that because it's a pure assembly program and the sections aren't technically needed? If so, how do I specify those sections (and do I even need to) for linking with a C (gcc) program using ld?
Forgive my inexperience here. I understand assembly on the x86 for the most part, I'm just not as familiar with the link step as I need to be. This project will end up getting me *very* used to the link step, especially when I start needing to load .elf programs with the kernel. ^_^
Thanks
Also, I noticed that the FASM example that you gave (which is amazing, btw, thanks a bunch for that) doesn't specify the sections. Is that because it's a pure assembly program and the sections aren't technically needed? If so, how do I specify those sections (and do I even need to) for linking with a C (gcc) program using ld?
Forgive my inexperience here. I understand assembly on the x86 for the most part, I'm just not as familiar with the link step as I need to be. This project will end up getting me *very* used to the link step, especially when I start needing to load .elf programs with the kernel. ^_^
Thanks
Re: Starting Out with FASM
For combining C and ASM your best to ask in the fasm forum, as i am a 100% only programmer, but theres Clib examples in the fasm source code its self, also you can use something like this, in fasm
It all depend on the output format you want.
Sorry can not help with C, but remember not only is fasm the best assembler for OS Dev, (it was made in the first place to write a OS), but also its the esiest to port, once your OS can load and save files, along with base print function etc, it will take less than half a hour.
Code: Select all
section '.text' executable align 16
Sorry can not help with C, but remember not only is fasm the best assembler for OS Dev, (it was made in the first place to write a OS), but also its the esiest to port, once your OS can load and save files, along with base print function etc, it will take less than half a hour.
Re: Starting Out with FASM
This part may be different for you depending on your toolchain. To link an assembly file with LD you should the following at the beginning of the assembly file. Then do tell fasm to output the file as a .o file. Then just add the new file to the list for LD. Again this part may vary depending on your toolchain.
Calling a C Function from Assembly
Assembly file
It also works for data.
Calling an Assembly function from C
Assembly file
C File
Code: Select all
FORMAT ELF
Assembly file
Code: Select all
extrn symbol_name
;then
jmp symbol_name or
call symbol_name
Calling an Assembly function from C
Assembly file
Code: Select all
public symbol_name
symbol_name:
ret
Code: Select all
// example function prototype
void func( int num ); or
extern void func( int num );
then call with func( 5 );
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thegamefreak0134
- Posts: 14
- Joined: Thu Jan 08, 2009 1:54 am
Re: Starting Out with FASM
frank wrote:Calling a C Function from AssemblyCode: Select all
FORMAT ELF
Assembly fileIt also works for data.Code: Select all
extrn symbol_name ;then jmp symbol_name or call symbol_name
I was using "extern" but the FASM syntax is "extrn". Darn my proper spelling habit, it's going to kick me a few times on this road.
Well, I made an "oh duh" while I was doing all of this: I realized that the assembly bit isn't even necessary in the Bare Bones tutorial, which I was basing my skeleton on. Basically, all the assembly bit does is pass in the multiboot header and set up a stack. Trouble is, GRUB will already happily do this for you if you compile to ELF format instead, and since the tutorial uses GRUB I can't fathom why it would be so redundant. I see its point, really I do, since it makes the code truly multi-boot compliant, but in the end I'm planning on ditching GRUB and writing my own bootloader anyway, which defeats the purpose really. So at this point, I'm tucking it away on the backburner in case I decide that I need it later.
That said, it's still extremely useful to now be able to link against FASM-generated code, now I can ditch NASM for good. You're all been a great help and I'm happy to report that I have nothing more to ask on this front for now. Thanks again!
-Nick