dis88 Beta Release 87/09/01 --- G. M. HARDING POB 4142 Santa Clara CA 95054-0142 "Dis88" is a symbolic disassembler for the Intel 8088 CPU, designed to run under the PC/IX operating system on an IBM XT or fully-compatible clone. Its output is in the format of, and is completely compatible with, the PC/IX assembler, "as". The program is copyrighted by its author, but may be copied and re- distributed freely provided that complete source code, with all copyright notices, accompanies any distribution. This provision also applies to any modifications you may make. You are urged to comment such changes, giving, as a miminum, your name and complete address. This release of the program is a beta release, which means that it has been extensively, but not exhaustively, tested. User comments, recommendations, and bug fixes are welcome. The principal features of the current release are: (a) The ability to disassemble any file in PC/IX object format, making full use of symbol and relocation information if it is present, regardless of whether the file is executable or linkable, and regardless of whether it has continuous or split I/D space; (b) Automatic generation of synthetic labels when no sym- bol table is available; and (c) Optional output of address and object-code informa- tion as assembler comment text. Limitations of the current release are: (a) Numeric co-processor (i.e., 8087) mnemonics are not supported. Instructions for the co-processor are disassembled as CPU escape sequences, or as interrupts, depending on how they were assembled in the first place. This limitation will be addressed in a future release. (b) Symbolic references within the object file's data segment are not supported. Thus, for example, if a data segment location is initialized to point to a text segment address, no reference to a text segment symbol will be detected. This limi- tation is likely to remain in future releases, because object code does not, in most cases, contain sufficient information to allow meaningful interpretation of pure data. (Note, however, that symbolic references to the data segment from within the text segment are always supported.) As a final caveat, be aware that the PC/IX assembler does not recognize the "esc" mnemonic, even though it refers to a completely valid CPU operation which is documented in all the Intel literature. Thus, the corresponding opcodes (0xd8 through 0xdf) are disassembled as .byte directives. For reference, how- ever, the syntactically-correct "esc" instruction is output as a comment. To build the disassembler program, transfer all the source files, together with the Makefile, to a suitable (preferably empty) PC/IX directory. Then, simply type "make". To use dis88, place it in a directory which appears in your $PATH list. It may then be invoked by name from whatever directory you happen to be in. As a minimum, the program must be invoked with one command-line argument: the name of the ob- ject file to be disassembled. (Dis88 will complain if the file specified is not an object file.) Optionally, you may specify an output file; stdout is the default. One command-line switch is available: "-o", which makes the program display addresses and object code along with its mnemonic disassembly. The "-o" option is useful primarily for verifying the cor- rectness of the program's output. In particular, it may be used to check the accuracy of local relative jump opcodes. These jumps often target local labels, which are lost at assembly time; thus, the disassembly may contain cryptic instructions like "jnz .+39". As a user convenience, all relative jump and call opcodes are output with a comment which identifies the physical target address. By convention, the release level of the program as a whole is the SID of the file disrel.c, and this SID string appears in each disassembly. Release 2.1 of the program is the first beta release to be distributed on Usenet.