boot/mkfhead.s

   1 !       Mkfhead.s - DOS & BIOS support for mkfile.c     Author: Kees J. Bot
   2 !                                                               9 May 1998
   3 !
   4 ! This file contains the startup and low level support for the MKFILE.COM
   5 ! utility.  See doshead.ack.s for more comments on .COM files.
   6 !
   7 .sect .text; .sect .rom; .sect .data; .sect .bss
   8 .sect .text
   9
  10 .define _PSP
  11 _PSP:
  12         .space  256                     ! Program Segment Prefix
  13
  14 mkfile:
  15         cld                             ! C compiler wants UP
  16         xor     ax, ax                  ! Zero
  17         mov     di, _edata              ! Start of bss is at end of data
  18         mov     cx, _end                ! End of bss (begin of heap)
  19         sub     cx, di                  ! Number of bss bytes
  20         shr     cx, 1                   ! Number of words
  21  rep    stos                            ! Clear bss
  22
  23         xor     cx, cx                  ! cx = argc
  24         xor     bx, bx
  25         push    bx                      ! argv[argc] = NULL
  26         movb    bl, (_PSP+0x80)         ! Argument byte count
  27 0:      movb    _PSP+0x81(bx), ch       ! Null terminate
  28         dec     bx
  29         js      9f
  30         cmpb    _PSP+0x81(bx), 0x20     ! Whitespace?
  31         jbe     0b
  32 1:      dec     bx                      ! One argument character
  33         js      2f
  34         cmpb    _PSP+0x81(bx), 0x20     ! More argument characters?
  35         ja      1b
  36 2:      lea     ax, _PSP+0x81+1(bx)     ! Address of argument
  37         push    ax                      ! argv[n]
  38         inc     cx                      ! argc++;
  39         test    bx, bx
  40         jns     0b                      ! More arguments?
  41 9:      movb    _PSP+0x81(bx), ch       ! Make a null string
  42         lea     ax, _PSP+0x81(bx)
  43         push    ax                      ! to use as argv[0]
  44         inc     cx                      ! Final value of argc
  45         mov     ax, sp
  46         push    ax                      ! argv
  47         push    cx                      ! argc
  48         call    _main                   ! main(argc, argv)
  49         push    ax
  50         call    _exit                   ! exit(main(argc, argv))
  51
  52 ! int creat(const char *path, mode_t mode)
  53 !       Create a file with the old creat() call.
  54 .define _creat
  55 _creat:
  56         mov     bx, sp
  57         mov     dx, 2(bx)               ! Filename
  58         xor     cx, cx                  ! Ignore mode, always read-write
  59         movb    ah, 0x3C                ! "CREAT"
  60 dos:    int     0x21                    ! ax = creat(path, 0666);
  61         jc      seterrno
  62         ret
  63
  64 seterrno:
  65         mov     (_errno), ax            ! Set errno to the DOS error code
  66         mov     ax, -1
  67         cwd                             ! return -1L;
  68         ret
  69
  70 ! int open(const char *path, int oflag)
  71 !       Open a file with the oldfashioned two-argument open() call.
  72 .define _open
  73 _open:
  74         mov     bx, sp
  75         mov     dx, 2(bx)               ! Filename
  76         movb    al, 4(bx)               ! O_RDONLY, O_WRONLY, O_RDWR
  77         movb    ah, 0x3D                ! "OPEN"
  78         jmp     dos
  79
  80 ! int close(int fd)
  81 !       Close an open file.
  82 .define _close
  83 _close:
  84         mov     bx, sp
  85         mov     bx, 2(bx)               ! bx = file handle
  86         movb    ah, 0x3E                ! "CLOSE"
  87         jmp     dos
  88
  89 ! void exit(int status)
  90 ! void _exit(int status)
  91 !       Return to DOS.
  92 .define _exit, __exit, ___exit
  93 _exit:
  94 __exit:
  95 ___exit:
  96         pop     ax
  97         pop     ax                      ! al = status
  98         movb    ah, 0x4C                ! "EXIT"
  99         int     0x21
 100         hlt
 101
 102 ! ssize_t read(int fd, void *buf, size_t n)
 103 !       Read bytes from an open file.
 104 .define _read
 105 _read:
 106         mov     bx, sp
 107         mov     cx, 6(bx)
 108         mov     dx, 4(bx)
 109         mov     bx, 2(bx)
 110         movb    ah, 0x3F                ! "READ"
 111         jmp     dos
 112
 113 ! ssize_t write(int fd, const void *buf, size_t n)
 114 !       Write bytes to an open file.
 115 .define _write
 116 _write:
 117         mov     bx, sp
 118         mov     cx, 6(bx)
 119         mov     dx, 4(bx)
 120         mov     bx, 2(bx)
 121         movb    ah, 0x40                ! "WRITE"
 122         jmp     dos
 123
 124 ! off_t lseek(int fd, off_t offset, int whence)
 125 !       Set file position for read or write.
 126 .define _lseek
 127 _lseek:
 128         mov     bx, sp
 129         movb    al, 8(bx)               ! SEEK_SET, SEEK_CUR, SEEK_END
 130         mov     dx, 4(bx)
 131         mov     cx, 6(bx)               ! cx:dx = offset
 132         mov     bx, 2(bx)
 133         movb    ah, 0x42                ! "LSEEK"
 134         jmp     dos
 135
 136 !
 137 ! $PchId: mkfhead.ack.s,v 1.3 1999/01/14 21:17:06 philip Exp $