OBJ2ASM: Object File Disassembler
obj2asm disassembles object (.obj) files in Intel OMF, Microsoft 32 and 64 bit COFF format, Linux ELF or Mac OS X Mach-O format, and writes out the corresponding assembler source code. (dmc++ generates Intel OMF format object files.) It works with the dmd D compiler, too.
16, 32 and 64 bit Intel x86 instruction sets are supported.
obj2asm automatically recognizes the object file format and instruction set to be disassembled.
Looking at the assembly language output of the compiler is highly useful for:
- Understanding how various language constructs are compiled.
- Trying various ways of expressing an algorithm to see which ones produce faster code.
- If a particular function needs to be rewritten in inline assembly and hand optimized for maximum speed, the obj2asm output forms a good starting point.
- Due to the large number of function calling conventions supported, sometimes it is necessary to verify that the correct convention is being used.
- Verifying correct code generation.
- Comparing output with other compilers.
- Learning assembly language.
Compiling the file with the -gl option embeds line number information in the object file, enabling obj2asm to match the source code up with the generated assembler instructions. Compiling the file with the -g option embeds debug records in the object file, which obj2asm will format and output.
Syntax
obj2asm commands have the following format:
obj2asm [-l -o -x] objectfile[.obj] [sourcefile] [-coutfile[.cod]]
| Arguments | Description |
|---|---|
| objectfile | the object file to disassemble. The extension defaults to .obj |
| sourcefile | the file compiled to produce the object file. Use this if the source file name embedded in the object file is missing or incorrect |
| -l | omit code labels in the assembly language file generated. Useful when comparing two object files; helping highlight the differences between them |
| -o | emit object code for each assembly language instruction |
| -x | emit code segment offset for each instruction |
| -coutfile | write output to outfile instead of the standard output. The default extension for outfile is .cod |
Example
To see the code generated by compiling test.cpp, use the following commands:
dmc -c -gl test obj2asm test
Note: Although the output of obj2asm is in masm format, it usually requires a little editting before masm will accept it.
File Formats Supported
- Tool Interface Standards (TIS) Relocatable Object Module Format (OMF) Specification Version 1.1
- Microsoft Codeview 4.0 Symbolic Debug Information Specification
- D programming language extensions to Codeview
- Microsoft COFF
- Tool Interface Standard (TIS) Executable and Linking Format (ELF) Specification Version 1.2
- Mac OS X Mach-O
Getting Obj2asm
obj2asm comes as part of the C/C++ Development System or the Extended Utility Package.