stnolting/neorv32

[feature request] Makefile: Additional CXX_USER_FLAGS only for C++ Compilation

jpf91 opened this issue · 3 comments

jpf91 commented

Is your feature request related to a problem? Please describe.

When compilling C++ code, I sometimes need flags which are not valid for C code, for example -fno-rtti -fno-use-cxa-atexit -fno-threadsafe-statics. I can just pass them to USER_FLAGS, but then they also get passed when compiling C files. in that case, GCC complains with warnings:
cc1: warning: command-line option '-fno-rtti' is valid for C++/D/ObjC++ but not for C

Describe the solution you'd like
Split CC_OPTS into C_OPTS and CXX_OPTS. Introduce CXX_USER_FLAGS and only use those for CXX_OPTS and in cpp compilation.

Though I guess there are other options to implement this as well. In the end, anything that allows specifying flags in the user Makefile that only get passed to the C++ compiler should work.

jpf91 commented

In addition, it would be nice to have a variable only affecting link flags. AFAIK -fwhole-program behaves differently at compile and link time.

stnolting commented

Hey @jpf91!

Sounds like a good idea! However, I am not an experienced C++ user... 🙈 Would you draft a PR so we can see which way this is going? 😉

jpf91 commented

Hey @stnolting

I've drafted a PR in #862 . It seems those variables even have somewhat standardized names, I always thought it's just a convention.

I didn't any flags yet, as that is a completely different and probably controversial topic :-)
For example, I recently experimented with -flto and -fwhole-program which worked fine when executing code from IRAM but broke execution in XIP mode. I still don't know why ;-)

But this change alone should enable users to specify any C++ and/or linker flags by themselves. I guess we can continue the discussion in #862

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