Hey, I'm making a ... specialty ... disassembler, but I need to figure out a nice, stable instruction set that it will work with. I have disasmed several HLL programs (with Olly) and see that many include some libraries from who-knows-where that have quite a bit of FPU workings.

This project is in it's early stages of planning, and what I really need to do is make a list (smaller preferably) of instructions that will cover the majority of programs, but my main roadblock is FPU. I haven't used it before, and if you have could you please list the most common instructions used in FPU, that will cover 90% of FPU-using programs?

No more giving back...

Hmm, okay. I decided that I will only length-disassemble FPU instructions, but that clears things up. Thanks!

A bit of advertisement

All x87 FPU instructions:

http://ref.x86asm.net/coder32.html#xD8

The column that goes right before the mnemonic column indicates if the instruction pops the stack (p), or pushes (s), or pops twice (P).

Hmm, thank you MazeGen.

My current step is to list all of the instructions that I will support, along with every possible form and thus opcodes that the disassembler will have to look for.

I decided to split it up into a length disassembler (to catch instructions that I don't support, marking them non-mutatable for next step), then processing the opcodes that I do know. Should work fine.

Why reinvent wheel? Use some existing disassembler. There is great one free opensource (BSD license) called DiStorm, google it.

Not a disassembler per-se, but its a debugger that includes disassembly support (they all need it), made by Feryno. It is 64-bit, but since this is for intel, it has to support all the 32-bit instructions too (except maybe push r32, i dont think your allowed to do any 32-bit push/pop in 64-bit), but anyway.. its just something for you to read over if you want, and the source is all fasm syntax.

http://board.flatassembler.net/topic.php?t=5045

We all have to start learning somewhere. I saw this as a way for AlexP to get a feel for the CPU instructions and disassemblers etc. I see nothing wrong with writing some code and learning.

Why reinvent the car? The Ford model-T was cheap and reliable, just buy one and stop the car makers from wasting their time to reinvent.

As for learning, it is a very good lesson of course, I too learnt instruction encoding by writing disassembler.

But if he wants to "get program done", not learn, in that case I suggest to use existing disasm.

By the way, there is very little i could imagine that could be improved in DiStorm.

Exactly, plus it's not something that I can use a normal disassembler for. Maybe it would help me develop the main loop, but the nature of the beast is that it can be as un-optimized as I want.

The only catch is I cannot use any tables. this shouldn't be a problem at all, because the only disasmers I've seen with tables used were all LDE's. Again, I cannot use any existing disassembler, it is a limited set plus it will not be ... how should I say ... disasmed to something for humans.

It is part of a much larger project, but it is a very important part and I really like your suggestions. I have been looking at sources such as Olly's disasmer (in C, kind of odd style) and some LDE's. If I can agree on a good instr. set that will cover most programs (the disasmer will not cover anything but general-purpose instr.s), then all should go well.