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Text File | 1990-12-22 | 19.5 KB | 397 lines

O B J A S M An object file to assembly language file conversion utility INTRODUCTION ------------ Under normal compilation procedures, most programs are converted into an intermediate notation before being converted into executable code. This notation simplifies the process of managing large programs by allowing the programmer to divide a program into many modules. When changes are made to a module, the programmer need only compile that module rather than the entire program. For most 80x86 and compatible processors, this notation is stored in a .OBJ file. After compilation, the .OBJ file must be converted into a machine executable form. At this stage the various modules must be combined and any inter-module dependencies must be resolved. This process is called linking and is accomplished by LINK, LINK86, or PLINK86 (depending on which vendor you purchase it from). In order to accomplish this resolving, the inter-module dependancy information must be stored in the .OBJ file. This information normally consists of routine names, variable names, and other globally known quantities. For the most part, once a program has been compiled into its .OBJ file, there is no going back. There is no way to convert the .OBJ file back into its appropriate language. It is for that reason that many companies who wish to sell thier proprietary routines to programmers, do so in the .OBJ file form. Normally these companies send out a library file (.LIB). .LIB files contain one or more .OBJ files. The program which groups .OBJ files into an .LIB file is known as LIB, LIB86, or PLIB86. This method of distribution has made routine vendors happy for many years. But this distribution of encoded routines has meant headaches for programmers. Programmers who discovered bugs in the routines, or wanted to make enhancements had to contact the vendor and plead for help. The programmers were at the mercy of the routine vendors. Fortunately, OBJASM came along. OBJASM is a utility which can convert .OBJ files back into assembly language, much like a dis-assembler. Unlike a dis-assembler however, OBJASM is able to determine the names of the routines that it is dis-assembling. Globally known data names can be determined as well. OBJASM is also able to determine the segments of the original routines. Segments are logical/physical divisions of sections of routines, normal segments are code, data, stack, etc. With this additional knowledge, OBJASM is able to produce an assembly language listing which is easier to read, easier to understand, and easier to modify than normal dis-assembler output. OBJASM output is compatible with MASM version 4.0 or later. It runs under MS-DOS version 3.0 or later although it is able to process .OBJ files (as specified by INTEL, document order no. 121748-001) from many other 80x86 operating systems such as CPM-86, XENIX 80x86, OS/2 and more. I believe that the format for UNIX (it has .o files) is completely different. COMPILING OBJASM ---------------- OBJASM was written for Microsoft C version 4.0 or later, and there is a supplied 'make' file for that environment. To execute the 'make' file, set-up your Microsoft C environment and go to the directory which contains the OBJASM source files. Make sure that you have the Microsoft C utility programs reachable using your 'PATH' environment variable, and type 'MAKE O' from the dos prompt. The compilation will proceed to compile OBJASM for the large model. One of the modules (ouinsert.c) will give a compiler warning message, or may fail depending how picky you have set your compiler. The message has something to do with 'casting far pointer to long' or vice-versa. Make sure your compiler gives only a warning message and proceeds with the compilation process. The warning message can be ignored. Data structure fanatics: the program uses threaded balanced binary trees for many internal lists and the ouinsert module is the insert-into-a-list function. The root node of each tree has the tree's height (an integer) stored into one of the structures pointer type members. This is non-portable C code, but it's ok for most C compilers. These threaded balanced binary tree routines were taken from a set of generic list handling functions. The modules contained in OBJASM are as follows: omain.c main() processes command line and passes through input file oprocess.c dis-assembly/dumping controlling routines odisasm.c routines to dis-assembly the various kinds of 80x86 instructions oreport.c routines to display some of the internal lists (publics and externals) ooutput.c routines to display various pieces of the dis-assembled .OBJ routine orXXXXXX.c (all except oreport.c) routines to process the various INTEL standard .OBJ record formats oubuff.c buffer I/O routines for the input file ouinsert.c list insertion routine oufind.c list searching routine ounewtre.c list creation routine ouinitre.c initialize all lists oufmterr.c .OBJ format error handling routine ouget.c input file formating (into chars,ints,longs,etc) routines oumalloc.c internal memory allocation routine (with check for out of memory error) oustruct.c assembly language structure routines oextra.c additional information file processing routines In addition, some of the modules (omain for example) have some debugging statements conditionally compiled. If OBJASM exhibits strange behavior and you wish to trace it down, re-compile these modules with the /DDEBUG option (for MSC). This will define the preprocessor variable DEBUG, which will enable the conditionally compiled debugging statements. EXECUTING OBJASM ---------------- OBJASM is executed from the command line as: OBJASM -options filename OBJASM -options filename.OBJ If you are dis-assembling a .LIB file, then you must use your LIB, LIB86, or PLIB86 utility to extract the .OBJ files. All output is sent to standard output (normally the console), but can be re- directed using the '>' symbol. A normal OBJASM execution would look like this: OBJASM OMAIN >OMAIN.ASM The output would then be stored in the file omain.asm. Output contains tab (control-I) characters to seperate the various assembly language columns. A normal line format would appear as: [LABEL]: (tab) [INSTRUCTION] (tab) [OPERANDS] (tab) ;[COMMENT] start: mov ds,ax ; dummy comment The options currently available for OBJASM are as follows: Option Description ------ --------------------------------------------------------------- -4 Make MASM v4.0 compatible output (No retf) -a Add labels for better output (use with EXEOBJ) -h Add hex comments showing bytes dis-assembled -r Make RASM86 compatible output (special segment directives, etc) -c Set the minimum size in a code segment, this option is followed by a number which represents the new value. Eg. -c20 -s Set the minimum size in a data segment, this option is followed by a number which represents the new value. Eg. -s10 -f Specifies an additional information file. The additional information file must be given in parenthesis. Eg. -f(myfile) The additional information file's default extension is ".add", as in the example above, the file specified would be "myfile.add". For more information see the ADDITIONAL INFORMATION FILE section. Technical Information --------------------- Most information used in writing OBJASM was taken from the following public documents: INTEL 8086 RELOCATABLE OBJECT MODULE FORMATS (Order No. 121748-001) MICROSOFT OMF Specification (Dated February 18,1986; this is an edited copy of the INTEL document) MS-DOS ENCYCLOPEDIA These documents describe the .OBJ file format. Here is a quick summarization of the format. Each .OBJ file contains one or more records. Each record has a record type (which specifies its purpose), a record length, and record data (which depends on the record type). INTEL outlines 30 different record types, most of which are never used. MICROSOFT added to these record types and removed the ones which it didn't need. The record types which OBJASM supports are listed below. Record Type Type Name Description ----------- ----------- ----------------------------------- 80h THEADR Module Header Record 88h COMENT Comment Record 8Ah MODEND End of Module Record 8Ch EXTDEF External Dependancy Definition 90h PUBDEF Public Value Definition 96h LNAMES List of Internally Referenced Names 98h GRPDEF Group Definition 9Ah SEGDEF Segment Definition 9Ch FIXUPP Dependancy Fixing-up Record A0h LEDATA (Logically) Enumerated Data Record A2h LIDATA (Logically) Iterated Data Record B0h COMDEF Communal Value Definition B4h LEXTDEF Local External Definitions (C static routines) B6h LPUBDEF Local Public Definitions (??) B7h LPUBDF2 Local Public Definitions (?? Another case? ) B8h LCOMDEF Local Communal Value Definitions (??) The C modules which handle the records of the above formats are named by placing the characters "OR" before the type name and have a .C extension. For example, the module named "ORSEGDEF.C" contains the C routine to handle the segment definition records. INTEL defines these other record types which are not supported by OBJASM. Record Type Type Name Description ----------- ----------- ----------------------------------- 6Eh RHEADR R-Module Header Record 70h REGINT Register Initialization Record 72h REDATA Relocatable Enumerated Data Record 74h RIDATA Relocatable Iterated Data Record 76h OVLDEF Overlay Definition Record 78h ENDREC End Record 7Ah BLKDEF Block Definition Record 7Ch BLKEND Block End Record 7Eh DEBSYM Debug Symbols Record 82h LHEADR L-Module Header Record 84h PEDATA Physically Enumerated Data Record 86h PIDATA Physically Iterated Data Record 8Eh TYPDEF Type Definition Record 92h LOCSYM Line Numbers Record 94h LINNUM Line Number Record A4h LIBHED Library Header Record A6h LIBNAM Library Module Names Record A8h LIBLOC Library Module Locations Record AAh LIBDIC Library Value Dictionary MICROSOFT documents an obsolete method for generating communal records using the TYPDEF record. This obsolete method is not handled by OBJASM. The dis-assembler portion of OBJASM is a two pass process. The first determines where local labels and symbols need to be placed, and the second outputs the dis-assembled instructions (with the labels and symbols). To determine whether to dis-assemble instructions or data, OBJASM performs a look ahead operation on each byte of the data records. If the byte is a printable character, then successive bytes are checked as well. The main module has a two variables called 'code_string' and 'data_string' which are used to specify the minimum length of a string. The 'code_string' value is used in code segments while the 'data_string' value is used in data segments. If this minimum length of printable characters is exceeded, then the bytes will be output as a string. OBJASM is shipped with a value of 20 for 'code_string' and 3 for 'data_string'. They work well for most .OBJ files. Bytes which are not contained in strings are checked against an instruction lookup and processing routine. If it is determined that this byte will generate a valid instruction, then it is output as an instruction. All other bytes are output as simple data bytes. Some assemblers and compilers will generate .OBJ records which contain a portion of a string or instruction in one record and the remainder in the next .OBJ record. OBJASM does not handle this very well. Strings spanning more than one record will be divided. Instructions spanning more than one record will not be recognized. Output would look this this: String: db 'This is all o' it should be db 'This is all one string' db 'ne string' Instruction: db 0BBh it should be mov bx,MYSYMBOL dw MYSYMBOL OBJASM attempts to accomodates for this by keeping a 16 byte overlap area. This overlap area is checked before processing the end of a record. This helps alleviate the problem for objects which are smaller that 16 bytes, something which is true for all normal instructions. For some other interesting quirks in OBJASM, please read the sections titled "Differences in .OBJ files which cannot be detected" and "Features allowable in .OBJ format which are not translatable into MASMable code". ADDITIONAL INFORMATION FILE --------------------------- The additional information file, specified with the -f option, is another method of specifying information to OBJASM. Lines in this file take one of the following formats: Format: Example: SEG segname segtype SEG DRIVER CODE This specifies that the segment named "segname" should be considered either data or code. The segtype should be either CODE or DATA indicating which type is desired. Normally OBJASM determines the segment using the segment's name, but specifying the segment name and segment type in this way allows overiding this determination. Format: Example: var = segname : offset TableY = DRIVER : 128 TableX = DRIVER : 200h This specifies that a label should be placed within the segment "segname" at the offset "offset". This can be used to add labels to the dis-assembled code, and can also be used to overide the internal labels generated by OBJASM. Format: Example: segname : offset : datatype DRIVER : 200h : DW DRIVER : 202h : DD This directs OBJASM to avoid the instruction/string look-ahead process and output data of a specified type. OBJASM outputs a data directive within the specified segment named "segname", at the offset "offset". The "datatype" can be any of these values: DB, DW, DD, DF, DQ, or DT. These correspond to the MASM base data types. Although this last format allows direct control of how OBJASM outputs data, care must be taken to put OBJASM into a state where it can actually use this information. If OBJASM is processing data as an instuction, it cannot be directed to output a data directive in the middle of that instruction. For example: Additional information: .OBJ FILE: SOME_SEGMENT: 1 : DW 8B360200 MOV SI,[0002] this would direct OBJASM to output a word in the middle of the MOV instruction. In-order to accomplish this, the addtional information file would have to direct that the first byte of the MOV instruction was also a data byte. To get it to work, you would have to have this: Additional information: .OBJ FILE: SOME_SEGMENT: 0 : DB 8B db 08Bh SOME_SEGMENT: 1 : DW 3602 dw 0236h 00 ... Other ----- Yes, there always is a section which defies categorization... The OBJASM program being continually refined. If you have any comments about its execution, wish to add features to it, or need to report a bug(s), please contact: Robert F. Day 19906 Filbert Drive Bothell, WA 98012 (206) 481-8431 The following section is a list of bugs that could not be fixed before shipping OBJASM. Please read the bug and problems lists to familiarize yourself with the known bugs and problem situations. The design notes are included to help you help me in refining OBJASM. If you need (or want) to add features to OBJASM, please contact me. We may be working on a similar addition and we may be able to save you some time. ------------------- Bugs to Dec 14 1990 ------------------- 1. TYPDEF records are ingored (I had some Digital Research Libraries which used TYPDEF records, but Microsoft doesn't use them). 2. Some languages generate segment names which are the same as the names of labels within the segment. MASM won't allow this. Please rename the segment, if possible. -------------------------------------------------- Differences in .OBJ files which cannot be detected -------------------------------------------------- (1) if label2 = label1 + 010h MOV AX,label1 + 0010h ; Might have been like this and MOV AX,label2 ; OBJASM will generate this ; (Evaluates to equivalent address) Reason: Public labels are resolved in local code before being sent to the linker. Although the .OBJ specifications allow two places to store symbol addition information (above, the 0010h), MASM only uses one of them. This is a probable source of some other .OBJ differences. MASM automatically computes the offset of the public symbol and creates a fixup record indicating that the offset of the segment added to the offset of the public within the segment should be used (rather than just a fixup indicating that the offset of the public should be used). Handling: When resolving a reference to an address which is not equal to a public symbol, a new local symbol is created. ------------------------------------------------------------------------------- Features allowable in .OBJ format which are not translatable into MASMable code ------------------------------------------------------------------------------- (1) A piece of code like: DW _labeln - $ ; Relative (data form of local jmp/call) Reason: MASM will not compile the above line. It is an equivalent data representations for relative 'JMP's and 'CALL's where _labeln is the label to jump or call to. Handling: If OBJASM detects this type of code (almost all .OBJ files have it) then the data output function will substitute an actual value for the $ operator. This will be noted by a nasty comment. The dis-assembly output function will still work if they are truly 'JMP's or 'CALL's (Relative addressing is proceeded by the jump short or call short opcodes). ----------------- End of OBJASM.DOC