C/C++ Library for Evaluate ASM Codes

[Vic]

Hi everyone.

I'm looking for a tiny library in C/C++ (or binding) that able to:

- Evaluate simple x86/x64 assembly codes (execute codes from a string to get output).

- Each asm instruction has callback or hook (at least memory access instruction, for several special purposes, E.g. using ReadProcessMemory to read memory from other process, etc).

Maybe a little bit like a VM.

MOV RAX,$INPUT
ADD RAX,8
MOV RAX,[RAX] # eg. memory access instruction
MOV $OUTPUT,RAX

Hint me. Thanks.

[deepzero]

You are looking for an emulator. Check out e.g. https://www.unicorn-engine.org/

[Vic]

It's not a tiny library. I think it is not needed to write many codes to evaluate a simple asm expression.

Probably, anybody already wrote it. I'm searching more, or I will try to write it myself if not exists.

[deepzero]

Version 1 of the library has no dependency on QEMU, I think. You will find that x86 is surprisingly complex and your tiny library may not end up as tiny as you expect.

[kao]

You should decide what exactly you want to have:

1) engine that supports all x86/64 instructions, all registers, flags and memory accesses. In that case, you're most likely looking for an assembler + emulator.
NASM is quite nice opensource assembler, it takes text like "mov eax, 1234h" and produces x86/x64 code as bytes. https://github.com/netwide-assembler/nasm. Better known alternative is FASM - but it's written in assembly, so maintenance will be painful.
Unicorn is an emulator - it takes bytes, disassembles them to x86/x64 code and then emulates it.
You'll need a combination of both to achieve the desired result ("execute codes from a string to get output")

2) simple scripting engine which supports something-that-looks-like-x86-assembler, with a very limited set of instructions. Then take a look at ODBGScript sources, it's a good place to start.
https://github.com/x64dbg/ODbgScript/blob/master/ODbgScript/OllyLang.cpp
https://github.com/x64dbg/ODbgScript/blob/master/ODbgScript/OllyLangCommands.cpp

 

Edited May 19, 2022 by kao

[Vic]

Sorry for slow reply. Case 2 is satisfied my expect. I have also thought about some open source like:

- AsmJit at https://asmjit.com/

- OllyScript at http://www.openrce.org/downloads/details/182/OllyScript_Source_Code

- x64dbg (ExpressionParser) at https://github.com/x64dbg/x64dbg/blob/c37a4867c93134368397e5c3c4b77136df6bab6e/src/dbg/expressionparser.cpp#L78

Probably I will look at several existing classes in these projects. They released under the GNU and ZLib license.