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I've been doing C++ for a long long time, but I come from the land of Windows.

I've been handed a project that uses CMake. I've googled around trying to learn it.

I run cmake . I assume it always looks for CMakeLists.txt and generates makefiles.

This creates a bunch more cmake files and make files. I was then instructed to run make package. I assume package is just a target name that could be anything.

I then get errors:

c++: error: unrecognized command line option ‘-mthumb-interwork’ c++: error: unrecognized command line option ‘-mfloat-abi=hard’ c++: error: unrecognized command line option ‘-mfpu=neon’

I think those are due to the fact that I am trying to compile for a different architecture then the one I am on. I assume all the cmake files would set that up correctly for me. I also assume that nothing there is proprietary.

I see the line in the CMakeLists.txt

SET(CMAKE_CXX_FLAGS "-march=armv7-a -mthumb-interwork -mfloat-abi=hard -mfpu=neon -mtune=cortex-a9 -std=c++11 -O3")

If I look at the official cmake documentation, it says, and I quote "Flags for all build types." ....Not very helpful

I am thinking it isn't using the correct compiler, but I also don't see where in the CMakeLists.txt the compiler is specified at all.

The question is: Why would these flags be unrecognized?

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    Dear downvoters. Maybe you'd like to specify your reasoning for downvoting a perfectly legitimate question where efforts were described and obviosuly made, such that the poster can form a better question? Otherwise, we'll end up with the exact same thing posted yet again. Commented Jul 18, 2018 at 19:57
  • The question appears to be a run-on. It is not readily apparent what the problem or question is. Commented Jul 18, 2018 at 19:59
  • Ok, edited to be one single black and white question. Commented Jul 18, 2018 at 20:02
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    The flags are not recognized because you're invoking the wrong compiler. Have you tried make package VERBOSE=1? That should show you the command line calls. You may have to do something like CXX=<path-to-gcc-arm-cross-compiler> cmake <remaining-args> Commented Jul 18, 2018 at 20:19
  • VERBOSE=1 is the bees knees! Commented Jul 18, 2018 at 20:32

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In the Linux world, it's often assumed that you don't need to specify the compiler by name; instead you arrange for c++ to refer to the compiler. That may involve setting PATH, creating a shell alias or a symbolic link.

Apparently you already did so, as your compiler is being called and is complaining about standard GCC flags - clearly your compiler isn't GCC.

The CMakeLists.txt file however is very much assuming it's intended for GCC. Don't blame CMake for that. CMake is the tool, CMakeLists.txt are project-specific instructions. This is a problem of whoever created the particular CMakeLists.txt file.

There's no easy fix. There is a real possibility that the -mfpu=neon option to gcc was necessary for the program, and it's anyone's guess what you'll need on the other compiler.

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Standard makefiles assume that the compiler is specified by the CXX variable - that's the normal way to specify a cross-compiler.

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