The DCU32INT utility by Alexei Hmelnov.
Version 1.0

----------------------------------------------------------------------------
E-Mail: alex@monster.icc.ru
http://monster.icc.ru/~alex/DCU/
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Purpose.
--------

Parse Delphi 2.0-5.0 units (DCU) and convert their information into the close 
to Pascal form.

DCU32INT stands for DCU32 INTerface, because this program can't extract 
the complete Pascal source, but the extracted unit interface is almost 
correct (see Compiler Information Loss Limitations section for exceptions).

This program is a by-product of the FlexT project (see 
http://monster.icc.ru/~alex/FlexT/ for details), but 
I have done my best to make it useful.

Usage.
------
DCU32INT <Source file name> <Switches> [<Destination file name>]

Destination file may contain * to be replaced by the unit name or name and 
extension. If * is the last char in the name, it will be replaced by 
<Unit name>.int, else - by <Unit name>.
Destination file = "-" => write to stdout.

Switches (start with "/" or "-"):
 -S<show flag>* - Show flags (-S - show all), default: (+) - on, (-) - off
    I(+) - show Imported names
    T(-) - show Type table
    A(-) - show Address table
    D(-) - show Data block
    F(-) - show fixups
    V(-) - show auxiliary Values
    M(-) - don't resolve class methods
    C(-) - don't resolve constant values
    d(-) - show dot types
    v(-) - show VMT for objects and classes
 -I - interface part only
 -U<paths> = Unit directories
 -N<Prefix> = No Name Prefix ("%" - Scope char)
 -D<Prefix> = Dot Name Prefix ("%" - Scope char)

The Scope char symbol will be replaced in the name by "T" for types "C" for
constants and so on (see source for details).

In general, there are two main ways to run the program:
- without the -S switch - to produce the most close to the original Pascal 
  source output without superfluous details;
- with the -S switch to see a lot of additional information, which reflects 
  the internal structure of the DCU file, e.g. the values of some fields of
  unknown purpose (You can try to guess what they mean), the data structures
  representing the VMT of classes, RTTI of data types or the table of 
  addresses.
Of course, You can always select only a subset of additional information using 
the -S<flags>.

Validity.
---------

The DCU32INT utility have passed successfully the "parse all .\LIB" test 
for all the supported by it Delphi versions, i.e. it have parsed all units 
in the <DELPHI LOCATION>\LIB directory with no errors reported. 
See alllib<N>.bat files for examples of running the DCU32INT to parse
all .\LIB (Drawback: it's a DOS BAT file, so the long unit names will be
replaced by the corresponding 8.3 ones).

This success doesn't mean, however, that the underlying DCU specification is 
absolutely correct. So, please, send me your bug reports (see the section 
"Home page" for details).

History.
--------

In 1996 I first saw Delphi (1.0 and 2.0).

Before that time, in the beginning of 1994 I had a successful experience
of reconstructing the structure of TPU files. I was interested in
the methods used by Borland to effectively compile Pascal programs
(much more effective in the speed of compilation, than C compilers
do). The conclusion I have made then was that it is possible to 
reconstruct an unknown file structure when you have at hand a generator 
of these files (a compiler for the case of the Pascal units).

The structure of 16-bit DCU for Delphi 1.0 is similar (with minor
changes) to the structure of TPU files, so I have easily extended
the TPU viewer program to include the DCU files.

But the structure of 32-bit DCU was completely different, it gave
a reason to believe in the rumors that Borlands have bought somebody's
else technology to compile 32-bit code, and my first impression was
that it would be almost impossible to restore the structure of the
32-bit units. But I haven't had the FlexT system then.

Using FlexT it becomes very easy to experiment with the DCU32 format
specification. All I need to check the existence and correctness of some
data structure is to specify it in FlexT and to parse the test files.
No programming of reading and print procedures and recompiling of the
parse program is required.

So I started from the obvious from a cursory examination of the DCU32
files fact: the file begins with some header and then follows a list of
tagged records of different formats, the structure of which depend on the
tag. To analyze the structure of the record for some particular tag
we can always ask the compiler to generate as many such records as we need.

The fact, which made it very difficult to start the analysis of DCU32
files, is the extensive use of the data structures, which, by analogy with
OBJ files, I call indices. I.e. all the integer fields, which can take
more than 1 byte value, are encoded in the DCU32 file so, that 1s in the
first bits of the first byte (up to 4 bits) indicate, that additional bytes
are used to represent the value. So, the value of 0x12 is represented by one
byte with the value of 0x24, 0x1243 - two bytes: 0x0D 0x49, and so on,
and for the values which require all 4 bytes (more than 28 bits), the high
4 bits of the 1st byte are not used and filled with zeroes, and the value
is represented directly by the next 4 bytes. Subsequently, in Delphi 4.0
the 64-bit integers were introduced, to encode their values the 1st byte
takes the value of 0xFF, and the next 8 bytes represent the value.

So, the size of any data structure may differ depending on the values of
the indices contained in it, and to successfully parse the DCU32 file it is
required to detect these index fields. To do it I have written and analyzed
some test files which contain something like the following code:

const
  c1=$1;
  c12=$12;
  c123=$123;
  c1234=$1234;
  c12345=$12345;
  c123456=$123456;
  c1234567=$1234567;
  c12345678=$12345678;
  cm1=-$1;
  cm12=-$12;
  cm123=-$123;
  cm1234=-$1234;
  cm12345=-$12345;
  cm123456=-$123456;
  cm1234567=-$1234567;
  cm12345678=-$12345678;

The index field can be detected by the changes in its size and by
the fact that it often takes successive even numbers in the successive
records of the same type.

Detecting the record structure doesn't mean detecting its semantics.
The values of some indices remain uninterpreted. The criterion for
correctness is the successful parsing of the test file, without breaks
in the sequence of tagged records caused by the wrong size detected
for some record.

The results of this analysis are represented in the DCU32.rfi FlexT file.
Unfortunately, not all the information can now be represented in FlexT.
In particular, it can't represent the fact that some tagged records are
enumerated by the two number sequences: the sequence of data types and
the sequence of addresses, with the data type declaration being a member
of both sequences (the address for data type is reserved for its TypeInfo).
A lot of indices in the DCU32 records are references to addresses and data
types using these sequence numbers.

So, to completely restore the structure of DCU32 files, it was anyway
required to write the specialized program DCU32INT, which extracts almost
all the information in readable and close to Pascal syntax form. I call
this program DCU32INT and not DCU32PAS, because it is always possible
to extract an interface part of a DCU32 file, but I doesn't claim yet
that it can extract a Pascal file, which can be immediately compiled
to obtain the same DCU (a lot of work should be done to make it possible).

All the rest of the reconstruction of the DCU32 format had been done using
the DCU32INT program, but the FlexT parse results were still used when
something went wrong. The most complex thing here was to understand the
rules of assignment of the numbers in the sequence of addresses.

The Compiler Information Loss Limitations.
------------------------------------------

There are two kinds of limitations of the DCU32INT program:

1. The ones caused by some disadvantages in its implementation,
  which can be overcome later;
2. The ones caused by information loss in DCU after compiling Pascal
  source, which are inevitable.

Here we'll consider some of the latter limitations.

While converting Pascal source into DCU, Delphi compiler extracts from
source and stores into DCU only the information, which is necessary to
produce later an executable file and also, if required, a debug
information for this file. During this process the compiler performs
some simplifications, which cause information loss.

Examples:

1. Identifiers declared in implementation part and subroutines are discarded
  if the debug info checkbox doesn't checked.

2. Evaluation of expressions. Constant expressions are replaced by their
  values, so one can't determine, e.g. that CDM_FIRST = WM_USER+100,
  it will have the fixed value of $0464.
  
3. Resolution of rename types. The rename types (types, which are defined
  by declarations like THandle = integer), are replaced by their reference
  type, so all the references to the THandle type in the source code are
  replaced by the System.Integer type.
  
4. Merge of fields in the records with variants. The declaration like

  TVarRec = record
    case Byte of
      vtInteger:    (VInteger: Integer; VType: Byte);
      vtBoolean:    (VBoolean: Boolean);
    -----------------------------------------
  end;

  Is stored as

  TVarRec{88,7F9FF4C2}=record
    VInteger: Integer{F:2 Ofs:0};
    VType: Byte{F:2 Ofs:4};
    VBoolean: Boolean{F:2 Ofs:0};
    ----------------------------------
  end;

  where Ofs:_ is a field offset information. Of course, we can group
  the fields into cases according to their order and offsets (future work),
  but the information about case labels is lost here completely, and it can't
  be used, e.g. to display safely (Delphi version independent) the Variant
  type value using the TVarRec definition.

All the above mentioned limitations can be demonstrated by Delphi
browser and evaluator (those utilities are also limited by them).

So, the extracted Pascal code can cause some problems, if used in other
version of Delphi, than that, which produced the DCU.

Home page.
----------

The latest version of this program and all the related news will be available
at http://monster.icc.ru/~alex/DCU/

Please, send me (e-mail: alex@monster.icc.ru) bug reports (including the units 
which were not parsed correctly), but first check:
  1. that you have the latest version of DCU32INT,
  2. that this bug was not already reported at 
     http://monster.icc.ru/~alex/DCU/FAQ.htm (projected page name).

Collaboration.
--------------

If you'll create something useful using my program or information contained
in its source, or will substantially improve this program, please, send me 
your results. I'll publish all such programs, which I'll consider to be 
useful, at my site (including the links to their home pages, if available,
and/or other author information).

I can propose the following lines of improvements, which I'm not going to
develop myself in the nearest future:

1. The DCU32INT is a console application, but it would be interesting to 
  create some kind of DCU Browser as a GUI application.

2. The disassembler, which is used in DCU32INT, is VERY simple, it would be 
  useful to improve it. 

3. The ideal final result for this kind of program would be to restore 
  completely the Pascal source from DCU. Of course this problem 
  is VERY hard. More simple problem, but still VERY hard, is to produce
  the Pascal source, where all the procedures are ASSEMBLER. The easier 
  approach is to produce assembler procedures which could have incorrect
  semantics (e.g. DB instead of some opcodes), but still could be compiled 
  to produce correct executable. 

4. Compiler discards some names, and other information. We could create
  additional input file for DCU32INT, which could contain some additional 
  guess information for the DCU being parsed, e.g. names of unnamed local 
  variables or types, entry points in the procedure code or even additional 
  type declarations (which could be compiled using DCC32 into additional DCU
  and then extracted from it).

5. Personally, I prefer to use Delphi and not C++ Builder, but it could be 
  interesting to modify this program to enable it generate its output in 
  the close to C++ Builder syntax form (C++ syntax + Borland's extensions) 
  instead of Pascal. 
  
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                             IMPORTANT NOTE:

This software is provided 'as-is', without any expressed or implied warranty.
In no event will the author be held liable for any damages arising from the
use of this software.
Permission is granted to anyone to use this software for any purpose,
including commercial applications, and to alter it and redistribute it
freely, subject to the following restrictions:
1. The origin of this software must not be misrepresented, you must not
   claim that you wrote the original software.
2. Altered source versions must be plainly marked as such, and must not
   be misrepresented as being the original software.
3. This notice may not be removed or altered from any source
   distribution.
