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Dis51 8051 Hex-file Disassembler
Description
Dis51 is a simple 8051 disassembler for Unix-like systems. It may even
compile under Microsoft Windows, but that has never been tested. It takes
an object file in Intel Hex format as input, and outputs an assembly
language file. This disassembler assumes by default that everything in
memory is data, and nothing is code. It starts at any number of entry
points you give it on the command line, then follows the code through all
branches until no branches are left. It then outputs an assembly language
file which should assemble under any standard 8051 assembler. All data
memory is declared using "DB" directives.
Dis51 uses symbolic names for SFRs it knows about. To be compatible with
as many assemblers as possible, I only defined SFRs that I thought were
common to "standard" 8051s. If you need to add other SFRs (or special
function bits) then the source file to modify is global.c. It should be
self-explanatory how to modify it, I hope.
I wrote Dis51 mostly for fun. It was Labor Day weekend and I felt like
taking a break from studies, so I started sketching out how I would design
a disassembler. I probably spent no more than two weeks from preliminary
design to completion of testing. I have been using the disassembler for a
few months now with no problems. Another reason I created it was because
I spent one afternoon downloading every free 8051 disassembler I could
find on the web, and couldn't find a single one that compiled under
Solaris and successfully disassembled a HEX file. I sincerely believe
that such a program exists, I just couldn't find it. Thus, Dis51.
How to get it
Dis51 is free to download. Get it from
http://home.earthlink.net/~davesullins/software/dis51-0.5.tar.gz. It's
released under the GNU Public License (GPL), which means you can download
the program for free, you get the source code with it, you can change the
source code to suit your needs, and you can redistribute the program with
or without modifications as long as the person you distribute the program
to gets the same rights you were given. If you use some of the code in
your own program, then your own program should also be released under the
GPL.
Compiling Dis51
Dis51 should compile without changes on any Unix-like machine. It
probably even works under Microsoft Windows, but I don't have a compiler
to try it out. Let me know what results you get if you try this.
First you need to download the source code. If you have GNU tar, extract
the file using one of the following commands, depending on what GNU tar is
called on your system:
gtar xvfz dis51-0.5.tar.gz
tar xvfz dis51-0.5.tar.gz
If you do not have GNU tar, you can use the following command to extract
the source code:
cat dis51-0.5.tar.gz | gunzip -c - | tar -xvf -
Now change to the dis51-0.5 directory. Edit the Makefile if necessary.
If you do not have gcc on your system, change the first line from "CC=gcc"
to "CC=cc" or whatever your C compiler is called. Type "make" when you
are done and dis51 will be created.
Alternatively, you can use the libhexfile shared library. Just type "make
shared" instead of "make" to link with libhexfile. If you don't know
whether you have the libhexfile shared library installed then you probably
don't.
That's it! I apologize for the lack of a man page, but luckily it's a
pretty simple program. Copy the executable (called dis51) to a bin
directory and you're ready to go.
How to use it
Dis51 takes a Hex file as stdin and outputs an assembly file to stdout.
In its simplest form, you can use the following command line:
dis51 < file.hex > file.a51
Without any command line options, Dis51 uses the entry point 0. If you
want to use other entry points, list them on the command line. For
example, to disassemble a program starting at address 0 which also uses
the serial port interrupt vector at address 35:
dis51 0 35 < file.hex > file.a51
Optionally, you can give the first command line argument "-l" to output in
list format. To repeat the previous example in list format:
dis51 -l 0 35 < file.hex > file.a51
One problem with Dis51 is that it is unable to determine the target
address of an indirect jump (JMP @A+DPTR). Thus if your program contains
indirect jumps certain parts of code will not be disassembled. The
solution is to search through the disassembled output of dis51 for the JMP
@A+DPTR instruction. If you find this instruction, look for large chunks
of DB directives elsewhere in the program. If you find some DB directives
that you suspect are code and not data, then manually add the addresses of
these directives to the command line of dis51 and run it again. Hint: 80h
is the SJMP command. Lots of DB 80h directives alternated with other data
bytes is likely to be a jump table.
Bugs
Please send me a message at davesullins@earthlink.net if you think you
have found a bug.
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