1 dis88
2 Beta Release
3 87/09/01
4 ---
5 G. M. HARDING
6 POB 4142
7 Santa Clara CA 95054-0142
8
9
10 "Dis88" is a symbolic disassembler for the Intel 8088 CPU,
11 designed to run under the PC/IX operating system on an IBM XT
12 or fully-compatible clone. Its output is in the format of, and
13 is completely compatible with, the PC/IX assembler, "as". The
14 program is copyrighted by its author, but may be copied and re-
15 distributed freely provided that complete source code, with all
16 copyright notices, accompanies any distribution. This provision
17 also applies to any modifications you may make. You are urged
18 to comment such changes, giving, as a miminum, your name and
19 complete address.
20
21 This release of the program is a beta release, which means
22 that it has been extensively, but not exhaustively, tested.
23 User comments, recommendations, and bug fixes are welcome. The
24 principal features of the current release are:
25
26 (a) The ability to disassemble any file in PC/IX object
27 format, making full use of symbol and relocation information if
28 it is present, regardless of whether the file is executable or
29 linkable, and regardless of whether it has continuous or split
30 I/D space;
31
32 (b) Automatic generation of synthetic labels when no sym-
33 bol table is available; and
34
35 (c) Optional output of address and object-code informa-
36 tion as assembler comment text.
37
38 Limitations of the current release are:
39
40 (a) Numeric co-processor (i.e., 8087) mnemonics are not
41 supported. Instructions for the co-processor are disassembled
42 as CPU escape sequences, or as interrupts, depending on how
43 they were assembled in the first place. This limitation will be
44 addressed in a future release.
45
46 (b) Symbolic references within the object file's data
47 segment are not supported. Thus, for example, if a data segment
48 location is initialized to point to a text segment address, no
49 reference to a text segment symbol will be detected. This limi-
50 tation is likely to remain in future releases, because object
51 code does not, in most cases, contain sufficient information to
52 allow meaningful interpretation of pure data. (Note, however,
53 that symbolic references to the data segment from within the
54 text segment are always supported.)
55
56 As a final caveat, be aware that the PC/IX assembler does
57 not recognize the "esc" mnemonic, even though it refers to a
58 completely valid CPU operation which is documented in all the
59 Intel literature. Thus, the corresponding opcodes (0xd8 through
60 0xdf) are disassembled as .byte directives. For reference, how-
61 ever, the syntactically-correct "esc" instruction is output as
62 a comment.
63
64 To build the disassembler program, transfer all the source
65 files, together with the Makefile, to a suitable (preferably
66 empty) PC/IX directory. Then, simply type "make".
67
68 To use dis88, place it in a directory which appears in
69 your $PATH list. It may then be invoked by name from whatever
70 directory you happen to be in. As a minimum, the program must
71 be invoked with one command-line argument: the name of the ob-
72 ject file to be disassembled. (Dis88 will complain if the file
73 specified is not an object file.) Optionally, you may specify
74 an output file; stdout is the default. One command-line switch
75 is available: "-o", which makes the program display addresses
76 and object code along with its mnemonic disassembly.
77
78 The "-o" option is useful primarily for verifying the cor-
79 rectness of the program's output. In particular, it may be used
80 to check the accuracy of local relative jump opcodes. These
81 jumps often target local labels, which are lost at assembly
82 time; thus, the disassembly may contain cryptic instructions
83 like "jnz .+39". As a user convenience, all relative jump and
84 call opcodes are output with a comment which identifies the
85 physical target address.
86
87 By convention, the release level of the program as a whole
88 is the SID of the file disrel.c, and this SID string appears in
89 each disassembly. Release 2.1 of the program is the first beta
90 release to be distributed on Usenet.
91