[CMake] Toolchain file for TI in CMake 3.10: how do I override compiler options and specify tools?

[Cristian Adam]

On Sat, Feb 23, 2019 at 8:49 AM Jason Heeris <jason.heeris at gmail.com> wrote:

> I am trying to use CMake (3.10) to build an ANSI C project that may be
> compiled on PC with eg. GCC, but also needs to compile with Texas
> Instruments' compilers for their microprocessors. So I have about a million
> questions.
>
> According to[1] it seems like the way to do this is via a toolchain file.
> So I'm trying to write a toolchain file to use TI's compiler/linker/etc,
> which do not (always) take the same arguments as eg. GCC or Clang.
>
> Is there a complete list of tools I can override in a toolchain file?
> Specifically, I want to set the C compiler, C++ compiler, assembler and
> linker. I know about CMAKE_C(XX)_COMPILER, but what about the others? Are
> they documented anywhere? (I could guess, but I don't think that's wise.)
>
> As I mentioned, TI's tools aren't the same as GCC, so I need to pare back
> a lot of options and start from almost-scratch (there are some
> commonalities). Options like "-D" and "-I" are fine, which is good because
> then eg. target_include_directories() still works. But certain other flags
> are just going to cause errors. How do I completely remove all compile
> flags from the generated Makefiles and replace them with my own? I can do
> this:
>
> set(CMAKE_C_FLAGS ${MINIMAL_FLAGS} CACHE STRING "" FORCE)
> set(CMAKE_C_FLAGS_DEBUG ${MINIMAL_FLAGS} CACHE STRING "" FORCE)
> set(CMAKE_C_FLAGS_RELEASE ${MINIMAL_FLAGS} CACHE STRING "" FORCE)
> set(CMAKE_C_FLAGS_RELWITHDEBINFO ${MINIMAL_FLAGS} CACHE STRING "" FORCE)
> set(CMAKE_C_FLAGS_MINSIZEREL ${MINIMAL_FLAGS} CACHE STRING "" FORCE)
>
> But I *still* see flags in the generated makefiles that I didn't put there
> such as "--compile_only" and "--c_file=...". How do I get rid of these and
> specify what's correct for my toolchain? (Also, why do I need the CACHE
> STRING "" FORCE options? I pulled that out of various Stackoverflow posts
> but I have no idea why it's necessary. Is that documented? What about the
> configurations... where are they listed? Do I have them all?)
>
>
Regarding the CMAKE_<LANG>_FLAGS_<CONFIG> have a look at this blog post:
https://cristianadam.eu/20190223/modifying-the-default-cmake-build-types/

You "just" need to modify the CMAKE_<LANG>_FLAGS_<CONFIG>_INIT variables,
no need to force the cache entries.

The "Modules" CMake folder is your friend, you can see how CMake handles
other compilers.
For debugging use CMake's "--trace-expand" command line parameter.

Cheers,
Cristian.
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