File specific compiler options

[NicoHood]

Regarding #21 I generally want to enable LTO. However some files need to be compiled without LTO (you can use -fno-lto). However this is impossible with dmbs it seems. Do you know how to change/add compilation flags for single files? The only solution I can think of is to create multiple makefiles, which is a really bad idea, I already tried that.

Maybe a special target can be written for that file that can add additonal flags?

More details for my particular issue:
I got an inline asm function _micros Which I want to call with an inline asm call _micros. However the symbol name changes to this, when LTO is used. So I need to disabled LTO for this file. I did not found any other way. The number is also random:

00000000 l    d  .gnu.lto__micros.3cfd9897f8dbd587	00000000 .gnu.lto__micros.3cfd9897f8dbd587

Solution

gcc.mk (same for .c/.S files)

# Compiles an input C++ source file and generates a linkable object file for it
$(OBJDIR)/%.o: %.cpp $(MAKEFILE_LIST)
	@echo $(MSG_COMPILE_CMD) Compiling C++ file \"$(notdir $<)\"
	$(CROSS)-g++ -c $(BASE_CC_FLAGS) $(BASE_CPP_FLAGS) $(CC_FLAGS) $(CPP_FLAGS) $($(notdir $<)_FLAGS) -MMD -MP -MF $(@:%.o=%.d) $< -o $@

Makefile:

FastLED_compat.c_FLAGS = -fno-lto

Since every file must be unique #12 this should not be a problem if we do it like that.