# Build the kernel

# Folder the generated files will be placed in.
BUILDDIR ?= .build
# Build folder suffixes
OPTTAG = -opt
NOOPTTAG = -noopt
DBGTAG = -dbg
VERBOSETAG = -verbose

# C++
CXX = $(PREFIX)g++

CXXFLAGS_ARCH = -m64

CXXFLAGS_DEFAULT = -std=c++14 -ffreestanding -fno-pic -nodefaultlibs -nostdlib -nostdinc -I. -fno-rtti -fno-exceptions -Wno-write-strings -fno-stack-protector -mno-red-zone -g -gdwarf-2
CXXFLAGS_OPT = -O3 -fomit-frame-pointer
CXXFLAGS_WARNING = -Wall -Wextra -Werror -Wno-error=unused-parameter -Wno-non-virtual-dtor
CXXFLAGS_CLANG = -no-pie -Wno-error=unused-private-field -Wno-implicit-exception-spec-mismatch -Wno-error=unused-const-variable -Wno-unused-command-line-argument -Wno-unused-const-variable -fno-strict-aliasing
CXXFLAGS_GCC = -fno-tree-loop-distribute-patterns -no-pie -nostartfiles -Wstack-usage=1024 -Wno-error=stack-usage= -fno-threadsafe-statics
CXXFLAGS_NOFPU = -mno-mmx -mno-sse -mgeneral-regs-only
CXXFLAGS = $(CXXFLAGS_ARCH) $(CXXFLAGS_DEFAULT) $(CXXFLAGS_OPT) $(CXXFLAGS_NOFPU) $(CXXFLAGS_WARNING)
# Compiler specific flags
ifneq (,$(findstring clang,$(CXX)))
	COMPILER := CLANG
	CXXFLAGS += $(CXXFLAGS_CLANG)
else ifneq (,$(findstring g++,$(CXX)))
	COMPILER := GCC
	# g++ 6 does not support general-regs-only flag
	ifeq "$(shell expr `$(CXX) -dumpversion | cut -f1 -d.` \<= 6)" "1"
		CXXFLAGS := $(filter-out -mgeneral-regs-only,$(CXXFLAGS))
	endif
	CXXFLAGS += $(CXXFLAGS_GCC)
else
	COMPILER :=
endif

# Assembly
ASM = nasm
ASMFLAGS = -f elf64

# Additional build utilities
OBJCOPY = $(PREFIX)objcopy
STRIP = $(PREFIX)strip
AR = $(PREFIX)ar

# C Runtime objects
CRTBEGIN_OBJECT = $(shell $(CXX) $(CXXFLAGS) --print-file-name=crtbegin.o)
CRTEND_OBJECT = $(shell $(CXX) $(CXXFLAGS) --print-file-name=crtend.o)
# GCC library
 # Attention: libgcc.a must not use red-zone!
LIBGCC = $(shell $(CXX) $(CXXFLAGS) -print-libgcc-file-name )

# Subdirectories with sources
VPATH = $(sort $(dir $(CC_SOURCES) $(ASM_SOURCES)))

# Lists of object files that are generated by compilation:
# Note that the variables containing the input files are to be defined by
# the Makefiles prior to including this common.mk.
ifdef CRTI_SOURCE
	CRTI_OBJECT = $(addprefix $(BUILDDIR)/,$(addsuffix .o,$(CRTI_SOURCE)))
else
	CRTI_OBJECT = $(shell $(CXX) $(CXXFLAGS) --print-file-name=crti.o)
endif
ifdef CRTN_SOURCE
	CRTN_OBJECT = $(addprefix $(BUILDDIR)/,$(addsuffix .o,$(CRTN_SOURCE)))
else
	CRTN_OBJECT = $(shell $(CXX) $(CXXFLAGS) --print-file-name=crtn.o)
endif
CC_OBJECTS = $(addprefix $(BUILDDIR)/,$(CC_SOURCES:.cc=.o))
DEP_FILES = $(addprefix $(BUILDDIR)/,$(CC_SOURCES:.cc=.d) $(addsuffix .d,$(ASM_SOURCES)))
ASM_OBJECTS = $(addprefix $(BUILDDIR)/,$(addsuffix .o,$(filter-out $(CRTI_SOURCE) $(CRTN_SOURCE),$(ASM_SOURCES))))

# Dependency files
$(BUILDDIR)/%.d : %.cc $(MAKEFILE_LIST)
	@echo "DEP		$<"
	@mkdir -p $(@D)
	$(VERBOSE) $(CXX) $(CXXFLAGS) -MM -MT $(BUILDDIR)/$*.o -MF $@ $<

$(BUILDDIR)/%.asm.d : %.asm $(MAKEFILE_LIST)
	@echo "DEP		$<"
	@mkdir -p $(@D)
	$(VERBOSE) $(ASM) $(ASMFLAGS) -M -MT $(BUILDDIR)/$*.asm.o -MF $@ $<

# Object files
$(BUILDDIR)/%.o : %.cc $(MAKEFILE_LIST)
	@echo "CXX		$<"
	@mkdir -p $(@D)
	$(VERBOSE) $(CXX) -c $(CXXFLAGS) -o $@ $<

$(BUILDDIR)/%.asm.o : %.asm $(MAKEFILE_LIST)
	@echo "ASM		$<"
	@mkdir -p $(@D)
	$(VERBOSE) $(ASM) $(ASMFLAGS) -o $@ $<

# The standard target 'clean' removes the whole generated system, the object files, and the dependency files.
clean::
	@echo "RM		$(BUILDDIR)"
	$(VERBOSE) rm -rf "$(BUILDDIR)" "$(BUILDDIR)$(OPTTAG)" "$(BUILDDIR)$(NOOPTTAG)" "$(BUILDDIR)$(DBGTAG)" "$(BUILDDIR)$(VERBOSETAG)"

# Target issuing a nested call to make generating a fully optimized systems without assertions.
%$(OPTTAG):
	$(VERBOSE) $(MAKE) BUILDDIR="$(BUILDDIR)$(OPTTAG)" ISODIR="$(ISODIR)$(OPTTAG)" CXXFLAGS_OPT="-Ofast -fomit-frame-pointer -flto -march=westmere -DNDEBUG" $*

# Target issuing a nested call to make generating a non-optimized system.
%$(NOOPTTAG):
	$(VERBOSE) $(MAKE) BUILDDIR="$(BUILDDIR)$(NOOPTTAG)" ISODIR="$(ISODIR)$(NOOPTTAG)" CXXFLAGS_OPT="-O0" $*

# Target issuing a nested call to make generating a system optimized for debugging.
%$(DBGTAG):
	$(VERBOSE) $(MAKE) BUILDDIR="$(BUILDDIR)$(DBGTAG)" ISODIR="$(ISODIR)$(DBGTAG)" CXXFLAGS_OPT="-Og -fno-omit-frame-pointer" $*

# Target issuing a nested call to make generating a system with verbose output.
%$(VERBOSETAG):
	$(VERBOSE) $(MAKE) BUILDDIR="$(BUILDDIR)$(VERBOSETAG)" ISODIR="$(ISODIR)$(VERBOSETAG)" CXXFLAGS_OPT="-DVERBOSE" $*

# Documentation
help::
	@/bin/echo -e "" \
		"All targets exist in different flavours in addition to \e[2;3m<name>\e[0m:\n" \
		"\e[2;3m<name>\e[0;3m-noopt\e[0m, \e[2;3m<name>\e[0;3m-opt\e[0m, \e[2;3m<name>\e[0;3m-dbg\e[0m, and \e[2;3m<name>\e[0;3m-verbose\e[0m.\n" \
		"Targets suffixed with \e[3m-noopt\e[0m are compiled without optimizations,\n" \
		"\e[3m-opt\e[0m targets produce a highly optimized binary, while\n" \
		"\e[3m-dbg\e[0m targets only use optimizations not hindering debugging.\n" \
		"Targets suffixed with \e[3m-verbose\e[0m generate binaries including\n" \
		"verbose output (via \e[3mDBG_VERBOSE\e[0m), making such targets useful for debugging.\n" \
		"To get a verbose make output, clear VERBOSE, e.g. \e[3mmake VERBOSE=\e[0m.\n" \
		"The following targets are available (each target can be suffixed by \e[3m-noopt\e[0m\n" \
		"and \e[3m-verbose\e[0m):\n\n" \
		"	\e[3mall\e[0m      Builds $(PROJECT), generating an ELF binary\n\n"

# Print warnings, if appropriate
ifeq (,$(COMPILER))
$(warning Unknown (and potentially unsupported) compiler "$(CXX)"!)
endif

# Include dependency files (generated via gcc flag -MM)
ifneq ($(MAKECMDGOALS),clean)
-include $(DEP_FILES)
endif

# Phony targets
.PHONY: clean help