如何找出是什么引入了 AVX 标志

Question

I have a quite large x64 c++ program that is compiled with Visual Studio. There are two ways how do we compile it - one is with sln solution file (from IDE or through msbuild), another is through Makefile in VS command prompt (which then internally uses Visual Studio's cl.exe and link.exe).

Somehow I got into situation that binary build through Makefile produces executable with /AVX instructions enabled, and I don't want that , so I want to find out how to get rid of it.

I try to compile and link it without any parameters (especially without /arch:AVX). I hope that I compile and link the same sources and libs in both sln and Makefile.

What is the easy way how to find out where the AVX comes from? Project includes dozens of h/cpp files, around 40 own libs, 10 windows libs. How would you proceed?

Answer 1

The simple way, find an old PC without AVX, run your app in debugger, it'll crash with invalid instruction runtime error and will trap to debugger. This way you'll immediately find out what code compiled into that instruction.

Another, harder way, write a C# console app that disassembles the compiled DLL or EXE, and searches for AVX instruction. You'll need Gee.External.Capstone nuget package for disassembling, PeNet package for parsing into sections. Also this code to disassemble . The disassembleStreamEx method will return you the stream of the instructions. Search for X86InstructionGroup.AVX or X86InstructionGroup.AVX2 instructions, print addresses, then use eg WinDBG + PDB file to translate addresses into source code location.

Update: before doing that, search your codebase for files containing _mm256_ , and *.asm files. If you're lucky you won't have to do anything else.