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Interfacing NASM with g++ and VC++ 2017

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kanito73:
Hello friends

Today is the time to interface NASM with C++ using g++ and VC++ (2017). Do you know of a tutorial that I can use?

The examples in the manual demostrate how to call assembly functions and how to pass numerical arguments, but in particular I need to pass pointers to strings and data buffers from C++ to ASM. And also require to see how to link the object file in Windows using VC++, for Linux it already shows how to do it.

In advance, thanks for your help and comments

sonictk:
Hi there:

I _just_ wrote a tutorial about working with x64 assembly on Windows that covers this topic:

https://sonictk.github.io/asm_tutorial/

You can skip to the "Using assembly in C/C++ programs" section, or take a look at the code samples and build scripts in the accompanying code repository for the tutorial.

Hope this helps!

kanito73:
Hi !!!

Thanks for your response. I just opened the link and the tutorial appears to be pretty complete. I think it will be a good idea to read it entirely.

Thanks!!!

sonictk:

--- Quote from: kanito73 on February 15, 2019, 06:31:52 PM ---Hi !!!

Thanks for your response. I just opened the link and the tutorial appears to be pretty complete. I think it will be a good idea to read it entirely.

Thanks!!!

--- End quote ---

No problem. Feel free to post a comment on the blog or ping me on Twitter if something doesn't make sense!

kanito73:

--- Quote from: sonictk on February 15, 2019, 10:44:35 PM ---
--- Quote from: kanito73 on February 15, 2019, 06:31:52 PM ---Hi !!!

Thanks for your response. I just opened the link and the tutorial appears to be pretty complete. I think it will be a good idea to read it entirely.

Thanks!!!

--- End quote ---

No problem. Feel free to post a comment on the blog or ping me on Twitter if something doesn't make sense!

--- End quote ---


Hello

I'm still reading your tutorial, it is very complete and illustrative, congratulations! Finally reached the "The Microsoft x64 Calling Convention" and I have two doubts.

1. If I pass a pointer from C++ to ASM, is it considered an INTEGER VALUE and it is passed into the registers RCX/RDX/R8/R9 (or the stack if necessary) as a normal number? And if so, is it only the OFFSET and the current DATA SEGMENT is assumed to contain the data?

2. If I need to pass different size arguments (byte, word, dword, qword), are they passed as full 64-bits values and just have to extract the required size, for example CL, CX, ECX or RCX according to the parameter size in C++? And, I suposse that no matter if it is a signed or unsigned value, the assembly function processes the value in the required way depending on the expected data size, let be an unsigned integer or a signed integer (maybe in two's complement if highest bit is set)?

Regards,
and again, congratulations for your tutorial!

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