source: trunk/minix/boot/mkfhead.s@ 20

!       Mkfhead.s - DOS & BIOS support for mkfile.c     Author: Kees J. Bot
!                                                               9 May 1998
!
! This file contains the startup and low level support for the MKFILE.COM
! utility.  See doshead.ack.s for more comments on .COM files.
!
.sect .text; .sect .rom; .sect .data; .sect .bss
.sect .text

.define _PSP
_PSP:
        .space  256                     ! Program Segment Prefix

mkfile:
        cld                             ! C compiler wants UP
        xor     ax, ax                  ! Zero
        mov     di, _edata              ! Start of bss is at end of data
        mov     cx, _end                ! End of bss (begin of heap)
        sub     cx, di                  ! Number of bss bytes
        shr     cx, 1                   ! Number of words
 rep    stos                            ! Clear bss

        xor     cx, cx                  ! cx = argc
        xor     bx, bx
        push    bx                      ! argv[argc] = NULL
        movb    bl, (_PSP+0x80)         ! Argument byte count
0:      movb    _PSP+0x81(bx), ch       ! Null terminate
        dec     bx
        js      9f
        cmpb    _PSP+0x81(bx), 0x20     ! Whitespace?
        jbe     0b
1:      dec     bx                      ! One argument character
        js      2f
        cmpb    _PSP+0x81(bx), 0x20     ! More argument characters?
        ja      1b
2:      lea     ax, _PSP+0x81+1(bx)     ! Address of argument
        push    ax                      ! argv[n]
        inc     cx                      ! argc++;
        test    bx, bx
        jns     0b                      ! More arguments?
9:      movb    _PSP+0x81(bx), ch       ! Make a null string
        lea     ax, _PSP+0x81(bx)
        push    ax                      ! to use as argv[0]
        inc     cx                      ! Final value of argc
        mov     ax, sp
        push    ax                      ! argv
        push    cx                      ! argc
        call    _main                   ! main(argc, argv)
        push    ax
        call    _exit                   ! exit(main(argc, argv))

! int creat(const char *path, mode_t mode)
!       Create a file with the old creat() call.
.define _creat
_creat:
        mov     bx, sp
        mov     dx, 2(bx)               ! Filename
        xor     cx, cx                  ! Ignore mode, always read-write
        movb    ah, 0x3C                ! "CREAT"
dos:    int     0x21                    ! ax = creat(path, 0666);
        jc      seterrno
        ret

seterrno:
        mov     (_errno), ax            ! Set errno to the DOS error code
        mov     ax, -1
        cwd                             ! return -1L;
        ret

! int open(const char *path, int oflag)
!       Open a file with the oldfashioned two-argument open() call.
.define _open
_open:
        mov     bx, sp
        mov     dx, 2(bx)               ! Filename
        movb    al, 4(bx)               ! O_RDONLY, O_WRONLY, O_RDWR
        movb    ah, 0x3D                ! "OPEN"
        jmp     dos

! int close(int fd)
!       Close an open file.
.define _close
_close:
        mov     bx, sp
        mov     bx, 2(bx)               ! bx = file handle
        movb    ah, 0x3E                ! "CLOSE"
        jmp     dos

! void exit(int status)
! void _exit(int status)
!       Return to DOS.
.define _exit, __exit, ___exit
_exit:
__exit:
___exit:
        pop     ax
        pop     ax                      ! al = status
        movb    ah, 0x4C                ! "EXIT"
        int     0x21
        hlt

! ssize_t read(int fd, void *buf, size_t n)
!       Read bytes from an open file.
.define _read
_read:
        mov     bx, sp
        mov     cx, 6(bx)
        mov     dx, 4(bx)
        mov     bx, 2(bx)
        movb    ah, 0x3F                ! "READ"
        jmp     dos

! ssize_t write(int fd, const void *buf, size_t n)
!       Write bytes to an open file.
.define _write
_write:
        mov     bx, sp
        mov     cx, 6(bx)
        mov     dx, 4(bx)
        mov     bx, 2(bx)
        movb    ah, 0x40                ! "WRITE"
        jmp     dos

! off_t lseek(int fd, off_t offset, int whence)
!       Set file position for read or write.
.define _lseek
_lseek:
        mov     bx, sp
        movb    al, 8(bx)               ! SEEK_SET, SEEK_CUR, SEEK_END
        mov     dx, 4(bx)
        mov     cx, 6(bx)               ! cx:dx = offset
        mov     bx, 2(bx)
        movb    ah, 0x42                ! "LSEEK"
        jmp     dos

!
! $PchId: mkfhead.ack.s,v 1.3 1999/01/14 21:17:06 philip Exp $