Decompilation of programs
Revive the old program!
Many have long been initiated projects idle. Authors,
forever leaving a Down throw their utility, and spit on the
user and erase the source. Your soul is aching for these
programs? Sometimes not enough seemingly small things
differently, written Mountains code re-do the same thing
offensively ...
So, long ago there is an opportunity to revive anyone ever
written ZX Spectrum for the project!
Not much emphasis is given to the fact
that (and because many do not know or do not represent in
volume) now existing sources ALASM, PT3, PkUnZip, UnRar, RIP,
Pusher - decompiled. Version of the ZX Word, adapted ZS'om from
Samara, based on the author's decompiled code that ZS, however,
does not spread. ZIP-depakera engine in his own MMCM player is
also based on decompiled code, which is too long
not distributed (by Volga Soft). JPEGIF
laboratory of Sam Style began with decompilation JPEG viewer by
Alien Factory. AND so on. Sometimes decompile occurred
due to a misunderstanding of the fact that the source
were considered lost (in the JPEG engine JPEGIF,
UnRar). Authors rarely recovers its
program accidentally overwritten (Pusher). Sometimes the old
sources because of the greed of their holders proved obsolete,
because program many times and broke the finishing straight to
machine code, without source (ALASM). In the latter case is
Tip: if something appends to
machine code, ogranizuyte all these changes in the form of
source code (INCBIN original code, then a lot of ORG with
pieces of programs) and even then they all will not find when
you are camping this source!
Generally, the source may be
most strange events - such as my source Worms demo once
transferred from MASM in ALASM manual copying on paper, then
with a piece of paper. Sometimes, disappears one module of
source code on the disk of the author (EWS v1.1, STS v5.2). Or,
again, the author no one knows where the source is lost entirely
(Hrip) ...
Decompilation of the dump.
Interrupt the boot the desired program
After unpacking all the code blocks, unload the main block of
code (the program as any) to the desired starting address. This
block you will decompile. How to stop boot - another
tema.Obychno system programs are not protected enough to load
BASIC in the STS, to find the entrance and exit, then put a
breakpoint on the exit. If you have a shadow debugger (STS in
the ROM shadow service minitor or Unreal Speccy), it is even
easier. Program during the better not to upload - it can be in
this while defective, with the destruction of the
initialization, wrong content variables, etc.
If a program uses sophisticated
structures that are likely to lie outside of the program (for
example, the headline format, which operates the program - both
in PT3), add zeros to the end of this code block. And that then
have to manually search for all references to variables outside
of the program, elementary possible some miss, and the
structure becomes unmovable!
Get the code block in the ZX Turbo Disassembler (ZXD) by
Alex Inozemtsev. There are 2 versions ZXD: 1.0 (authoring,
unloads a ZX-ASM, more precisely, in the text with tabs,
special for ZX-ASM) and 1.1 (cracked by Viper / TL - unloads in
ascii, but I do not like there colors). I tried
use the first, for example, to decompile Mr Gluk Reset Service,
and the second - to decompile Pefrect Commander. STS'om
and DASM'om (by Jaguar / PHD) is better not to try - that
memory for the label came to an end, you will be very
unpleasant to find out when you already typed all the addresses
of data blocks in program.
So, what I mean. Mark means ZXD all the data (single-byte
DEFB, double-byte DEFW and long loadable INCL), to distinguish
them from the code Z80.
After the first crude arrangement of press
Make Labels on the menu, and on labels for certain
be able to find errors in your razbienii.Chem
the more you fix them back in ZXD, the less the need to
manually transfer from assembler code, and vice versa on the
next steps in ALASM.
Save the project just in case (there
and will lie your way to the partition) and the decompiled
program to disk.
If you enjoyed ZXD 1.0, then the texts
need to be translated into normal form, replacing
Custom ZX-ASM'ovskie tabs with spaces. This can be done in
ACEdit (I did therein).
Renewal of the dump.
Received a lot of texts to download
ALASM teams impOrt. It is advisable to load them into memory
all at once. Each file takes slightly less than half
ALASM'ovskoy pages, but combine them with the reserve -
approximately half the file on the page,
as they swell to comment and long labels. Cut on the Limits of
the procedures.
More procedures, which will find (if
not initially clear, then all tags
standing after RET absolute and unconditional JR / JP), mark
the "bookmarked" by separating label procedures to
stroki.Perehodit between They can be the cursor in Ext + L.
While you are walking on the program from end to end, notice
neoptimizirovannosti, Unused parts and repetitions, was
isolated from the line shift to the right (this I select the
right, and you can differently).
Changes nothing in the program will now!
On the contrary, periodically check that the code block that
you get when you assemble, identical to the one you dumped on
the ground etape.Dlya There are several programs "File
Comparer". I take such a program from Mayhem. Previously,
compared with writing a piece of code with XOR (Inconvenient,
when the unit takes more than half the memory). PT3 (most of my
first decompilation), I did not compare. Because of this
retained more than a hundred versions of the intermediate
decompiled source code (Hard to suddenly
into misery or something - where to get, with what
check?) Then during the heap versions shoveled errors. The
lesson to me and you.
Separately from the previous step (before
or after, but not both - distracted, as if chasing two hares)
translate all the constants in a convenient and understandable
form. If the constant is used in Playing as a character, then
let it be the letter (ZXD default does so), otherwise the
number. Sometimes decimal understandable 16-ary. On
amateur - binary. Naturally, the extra
zeros after the # is also no good.
In ZXD error - negative bias
for IX and IY had increased by 256. Not
surprised if will not compile. May still need to replace the XH
HX and the like.
To find out what all the encountered tag frequency
ispolzovaniya.Eto done as follows: replace the symbol L in the
label name to something another, and recompile. (You can
for several labels, if compiled for a long time. An emulator
with the turbo button things quickly.) then recover, as it was.
Result (how many times have popped up an error)
that he was not gone, write over metkoy.Vot
as follows:
3
L867F
2 error "not defined" and "wrong short"
should be considered for one. If the error
eye for more than 10, then write "many", it is
easier than figuring out how many exactly. If
number is small, then the mark may be
local to this procedure (check
replacing it with the name of the place and the immediate
appeals and recompile), then mark it as follows:
_867F
(And remove the number - it was not for local
useful). For non-local labels figure
1 or 2 may mean that the procedure is highlighted in the
process uneconomical. But in each If necessary to estimate and
compare the length code subroutine outside a subroutine and
contributed by inline (instead of calling for CALL simply write
its contents).
Tags, which are completely understood (such as
CLS procedures and DHL), rename, replace
all calls through a search and replace.
Can run into the mark, standing with the imperfect is not
the topic. They were there:
a) due to the fact that you have transferred manually
piece of code in the data;
b) due to the fact that some programs do not work melts with
those addresses (DISP);
c) due to the fact that part of the program zati raetsya
during the data;
d) due to the fact that it does not address and Cons tantalum
(like # 7ffd);
e) ...
In general, each case requires review.
Out in ALASM is a function of the text search.
Just look for circulation to the label on all
program modules. If it's still DISP,
place an appropriate site as DISPENT, and labels will have to
place (drag the program from other places because they
Logically already somewhere defined) manually.
Sometimes, the label is used exclusively
in unused procedures of the program (they
could be in the code accidentally, even with
other system addresses! For example, the author does not
clear the memory when compiling), in which case tick mark
somehow, then it can be removed. For example, all such labels,
as well as addresses of data external to to the program, I put
at the beginning of the first (main) source.
Variables in the body of the program ZXD draws as follows:
LD BC, 0
L67B4 EQU $ - # 0002
L67B5 EQU $ - # 0001
Them, I usually corrects for this:
L67B4 = $ +1
L67B5 = $ +2
LD BC, 0
However, the label L67B5, if it is used in the program only
once, it is better to this place is replaced by the expression
L67B4 +1. Similarly, for external data (where the adjacent
addresses can be identified, for example, when cleaning
LDIR'om. It makes sense to call labeled only at this address
less cleaning).
In no case can automate these processes. Because at the time
they you become acquainted with programmoy.Programma thing
thin. Program must be understood.
As a result, you will probably be moved (check by running
with different number of NOP'ov in different places), however,
obscure ishodnik.No, since he had already issued convenient to
use (similar to a program, not the dump), to understand it
better. Usually at spaced markers in the middle Programme for
7000 lines (somewhere 900 marks) takes a couple of weeks. This
is quite a creative process, but it almost always is. Can leave
some procedures without a name, if your planned changes in
program must be in other places. Then he will understand, in
the optimization process (Because you are some stations have
already tagged shift to the right - to optimize?) and
navorachivaniya.
All changes in the initial stage (when
you are still not very understand the program and
it may worsen) mark, for example,
shift lines to the left. Again, this is my
personal way, but it paid off. I mark the shifts and changes in
their own programs, and retracts the line back then, when sure
of their correctness and optimality.
A month later, the decompiled source code
no one is distinguished by the type of avtorskogo.Zhelatelno
its spread, as you yourself can also score for the project as a
writer.
A. Coder
