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