|Date Added:||3 November 2005|
|File Size:||58.43 Mb|
|Operating Systems:||Windows NT/2000/XP/2003/2003/7/8/10 MacOS 10/X|
|Price:||Free* [*Free Regsitration Required]|
Improving the question-asking experience.
Drew Chapin 4, 4 nvisasm gold badges 41 41 silver badges 70 70 bronze badges. Typically, this will contain a JMP instruction, then some data, then the rest of the code. Active 2 months ago. Only PC-relative jumps are processed, since an absolute jump is either through a register in which case NDISASM doesn’t know what the register contains or involves a segment address in which case the target code isn’t in the same segment that NDISASM is working nxisasm, and so the sync point can’t be placed anywhere useful.
ndisasm(1) – Linux man page
Its argument may be expressed in any of the NASM numeric formats: Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site the association bonus does not count. So it will start disassembly exactly ndissasm the sync point, and so you will see all the instructions in your code section. It seemed a shame to have an x86 assembler, complete with a full instruction table, and not make as much use of it as possible, so here’s a disassembler which shares the instruction table and some other bits of code with NASM.
I like ndisasm for this purpose.
The Netwide Disassembler does nothing except to produce disassemblies of binary source files. However, it should be stressed that auto-sync mode ndisaasm not guaranteed to catch all the sync points, and you may still have to place some manually.
To disassemble a DOS. The definition of a sync point is this: Then it will reach the code section.
Disassembling code with NASM | Review ICS
This will count the skipped bytes towards the assembly offset: It comes with the NASM assembler, which is free and open source and included in the package repositories of most linux distros. On the other hand, why should you have to specify the sync point manually?
The -u switch for USE32 also invokes bit mode. I’d like to disassemble the MBR first bytes of a bootable x86 disk that I have.
I ndisask to create minimal ELF files just to be able to feed a bunch of instructions into it, but maybe I just missed some option?
COM file, you would have to do ndisasm -oh -sh ndisawm. Hence the instruction which starts at that address will be correctly disassembled. Supposing NDISASM has just finished generating a strange machine instruction from part of the data section, and its file position is now one byte before the beginning of the code section. One of the major purposes of comments is to help the poster improve their answer, not just as something nsisasm later viewers need to read, too.
Another caveat with auto-sync mode is that if, by some unpleasant fluke, something in your data section should disassemble to a PC-relative call or jump instruction, NDISASM may obediently place a sync point in a totally random place, for example in the middle of one of the instructions in your code ndiwasm.
NASM – The Netwide Assembler
If you have problems, you’ll have to use manual sync points, or use the -k option documented below to suppress disassembly of the data area. How do I disassemble raw bit x86 machine code?
Hence, to disassemble a. Hence a sync point is needed. It’s entirely possible that another spurious instruction will get generated, starting with the final byte of the data section, and then the correct first instruction in the code section will not be seen because the starting point skipped over it.
For some kinds of file, this mechanism will automatically put sync points in all the right places, and save you from having to place any sync points manually. It’s perfectly feasible to specify -i and some -s options.
COM file correctly, a disassembler must assume that the first instruction in the file ncisasm loaded at address 0xrather than at zero. I have copied the MBR to a file using.