8086 Disassembler Download 90
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In essence, a disassembler is the exact opposite of an assembler. Where an assembler converts code written in an assembly language into binary machine code, a disassembler reverses the process and attempts to recreate the assembly code from the binary machine code.
Since most assembly languages have a one-to-one correspondence with underlying machine instructions, the process of disassembly is relatively straight-forward, and a basic disassembler can often be implemented simply by reading in bytes, and performing a table lookup. Of course, disassembly has its own problems and pitfalls, and they are covered later in this chapter.
Many disassemblers have the option to output assembly language instructions in Intel, AT&T, or (occasionally) HLA syntax. Examples in this book will use Intel and AT&T syntax interchangeably. We will typically not use HLA syntax for code examples, but that may change in the future.
Here we are going to list some commonly available disassembler tools. Notice that there are professional disassemblers (which cost money for a license) and there are freeware/shareware disassemblers. Each disassembler will have different features, so it is up to you as the reader to determine which tools you prefer to use.
Many of the Unix disassemblers, especially the open source ones, have been ported to other platforms, like Windows (mostly using MinGW or Cygwin). Some Disassemblers like otool ([OS X) are distro-specific.
Since data and instructions are all stored in an executable as binary data, the obvious question arises: how can a disassembler tell code from data? Is any given byte a variable, or part of an instruction?
Many interactive disassemblers will give the user the option to render segments of code as either code or data, but non-interactive disassemblers will make the separation automatically. Disassemblers often will provide the instruction AND the corresponding hex data on the same line, shifting the burden for decisions about the nature of the code to the user. Some disassemblers (e.g. ciasdis) will allow you to specify rules about whether to disassemble as data or code and invent label names, based on the content of the object under scrutiny. Scripting your own "crawler" in this way is more efficient; for large programs interactive disassembling may be impractical to the point of being unfeasible.
The general problem of separating code from data in arbitrary executable programs is equivalent to the halting problem. As a consequence, it is not possible to write a disassembler that will correctly separate code and data for all possible input programs. Reverse engineering is full of such theoretical limitations, although by Rice's theorem all interesting questions about program properties are undecidable (so compilers and many other tools that deal with programs in any form run into such limits as well). In practice a combination of interactive and automatic analysis and perseverance can handle all but programs specifically designed to thwart reverse engineering, like using encryption and decrypting code just prior to use, and moving code around in memory.
User defined textual identifiers, such as variable names, label names, and macros are removed by the assembly process. They may still be present in generated object files, for use by tools like debuggers and relocating linkers, but the direct connection is lost and re-establishing that connection requires more than a mere disassembler. Especially small constants may have more than one possible name. Operating system calls (like DLLs in MS-Windows, or syscalls in Unices) may be reconstructed, as their names appear in a separate segment or are known beforehand. Many disassemblers allow the user to attach a name to a label or constant based on his understanding of the code. These identifiers, in addition to comments in the source file, help to make the code more readable to a human, and can also shed some clues on the purpose of the code. Without these comments and identifiers, it is harder to understand the purpose of the source code, and it can be difficult to determine the algorithm being used by that code. When you combine this problem with the possibility that the code you are trying to read may, in reality, be data (as outlined above), then it can be even harder to determine what is going on. Another challenge is posed by modern optimising compilers; they inline small subroutines, then combine instructions over call and return boundaries. This loses valuable information about the way the program is structured.
Akin to Disassembly, Decompilers take the process a step further and actually try to reproduce the code in a high level language. Frequently, this high level language is C, because C is simple and primitive enough to facilitate the decompilation process. Decompilation does have its drawbacks, because lots of data and readability constructs are lost during the original compilation process, and they cannot be reproduced. Since the science of decompilation is still young, and results are "good" but not "great", this page will limit itself to a listing of decompilers, and a general (but brief) discussion of the possibilities of decompilation. Compared to disassemblers a decompiler generates code that doesnot require that one is familiar at the processor at hand. It may even be that the decompiled code can be compiled on a different processor, or give a reasonable starting point to reproduce the program on a different processor.
From a human disassembler's point of view, this is a nightmare, although this is straightforward to read in the original Assembly source code, as there is no way to decide if the db should be interpreted or not from the binary form, and this may contain various jumps to real executable code area, triggering analysis of code that should never be analysed, and interfering with the analysis of the real code (e.g. disassembling the above code from 0000h or 0001h won't give the same results at all).
See the Sourceforge download page for the last released version including source and binary packages for Linux - amd64, Microsoft Windows - x86, Microsoft Windows - amd64 and Mac OS X - ppc and amd64.
Major Linux distributions take care of SDCC installation packages themselves and you will find SDCC in their repositories. Unfortunately SDCC packages included in Linux disributions are often outdated. In this case users are encouraged to compile the latest official SDCC release or a recent snapshot build by themselves or download the pre-compiled binaries from Sourceforge download page.
Below is the full 8086/8088 instruction set of Intel (81 instructions total). Most if not all of these instructions are available in 32-bit mode; they just operate on 32-bit registers (eax, ebx, etc.) and values instead of their 16-bit (ax, bx, etc.) counterparts. The updated instruction set is also grouped according to architecture (i386, i486, i686) and more generally is referred to as (32-bit) x86 and (64-bit) x86-64 (also known as AMD64).
Causes #UD in Real mode and Virtual 8086 Mode - Windows 95 and OS/2 2.x are known to make extensive use of this #UD to use the 63 opcode as a one-byte breakpoint to transition from Virtual 8086 Mode to kernel mode.[2][3]
The VIA PadLock instructions are instructions designed to apply cryptographic primitives in bulk, similar to the 8086 repeated string instructions. As such, unless otherwise specified, they take, as applicable, pointers to source data in ES:rSI and destination data in ES:rDI, and a data-size or count in rCX. Like the old string instructions, they are all designed to be interruptible.
Free software, uploaded by the author. Index A B C D E F G H I J [K] L M N O P Q R S T U V W X Y Z KVL29EOSSummary:Hires graphics library for Eclipse (adv. GUI)License:FreewareAuthor:Grzegorz KowalEmail:kojak@yoyo.plDownload:kvl29eos.zip(Apr 7 2000, 115.9K)Description:Kojak's VESA Library 2.9 is a set of functions useful for the simplecreation of 32-bit GUI DOS programs under the Eclipse Operating System(DOS Extender). It supports VESA 1.x or 2.x BIOS in 640x480x256,800x600x256 and 1024x768x256 modes. The library implements macros andfunctions providing support for block, line and pixel operations,pallette manipulation, GIF, Color-IX bitmaps, text, filtered input,advanced graphic user interface, and more. Index A B C D E F G H I J K [L] M N O P Q R S T U V W X Y Z LOADEMSSummary:ASM example of load & execute from EMS memoryDownload:loadems.zip(Feb 25 1990, 3.1K) LW 8086/80186Summary:Pop-up help for instruction setDownload:lw86.zip(Nov 20 1986, 14.3K) Index A B C D E F G H I J K L [M] N O P Q R S T U V W X Y Z M68DISVersion:2.0Summary:Intelligent MC6800/6802 disassembler,License:FreewareDownload:m68dis20.zip(Nov 26 2000, 11K)Description:The M68DIS program is a disassembler for MC6800/6802. It's operationis controlled by a command file, which tells it what binary code imagefile(s) to load, the addresses for code entry points such as RST, NMI,etc. (optional), and the addresses for any code or subroutines whichmay not be explicitly called within the MC6800/6802 code. The programthen processes the code, tracing execution paths and identifying jumplocations, subroutines and data tables. The program output is normallyin "list" format, with an address column at the start of each line,however, this address column is omitted if the specified output filename ends in ".ASM". MAC 8080Summary:TASM macros to assemble codeDownload:mac8080.zip(Nov 24 1991, 9.9K) MASM_CN 6Summary:Converts v6.x .ASM to v5.x formatLicense:SharewareEmail:john.augustine@gmiibbs.comDownload:masm_cn3.zip(May 31 1997, 8K)Description:MASM converter converts the MASM v6.x Assembly Source Code (.ASM) to the format used by the older MASM v5.x assemblers. This allows you to assemble, after the conversion, the new source code with an older assembler (the author uses MASM v5.1). The new source code comes from such sources as a disk when you purchase an assembly related book, software distributors, etc. MASM32 V9.0Summary:32 bit MASM assembler from MicrosoftDownload: m32v9r.zip(3,455K) MASM ReferenceSummary:Microsoft MASM assembler reference manualDownload: MASMReference.pdf(646K) MD 8086Summary:Masterful Disassembler for Intel programsDownload:md86.zip(Jun 24 1990, 153.4K) MMXTASMSummary:Turbo Assembler macros for MMX programmingLicense:FreewareAuthor:Normand LeclercEmail:lecn1306@ele.etsmtl.caDownload:mmxtasm0.zip(Mar 14 1998, 6.8K)Description:Now TASM users can code for MMx processors with TASM. Based on Intel's iammx.inc file, I managed to create a new set of macros using Ideal programming mode. I have also included an example on how to use them and how they are transparent. The example is MSDOS based and I did not include a pre-compiled version, instead, I included a makefile for easy creation. The example uses case-sensitivity compilation but the macros will work well without it. This is still a beta release. I expect to have some bugs even if I tested every instructions. MODES 013hSummary:Switch to mode/03h without BIOS - ASM srcDownload:modes.zip(Jan 27 1997, 6.1K) MODEXSummary:High performance ASM video routinesDownload:modex105.zip(May 22 1996, 258.7K) MOUSEAPI Docs on the interrupt functions used to control the mouse in DOS. Download 2b1af7f3a8