per-config build output using VPATH

based on https://make.mad-scientist.net/papers/multi-architecture-builds/

example/Makefile

@@ -1,33 +1,48 @@
+# based on https://make.mad-scientist.net/papers/multi-architecture-builds/
+
+_libc := $(if $(LIBC),$(LIBC),gnu)
+ifeq (,$(filter gnu musl,$(_libc)))
+  _link_type := $(error "LIBC has to be set to one of: gnu, musl")
+endif
+
+_link_type := $(if $(LINK),$(LINK),dynamic)
+ifeq (,$(filter dynamic static,$(_link_type)))
+  _link_type := $(error "LINK has to be set to one of: dynamic, static")
+endif
+
+_profile := $(if $(PROFILE),$(PROFILE),release)
+ifeq (,$(filter release debug size-optimized,$(_profile)))
+  _profile := $(error "PROFILE has to be set to one of: debug, release, size-optimized")
+endif
+
+ARCH ?= $(shell uname -m)
+RUST_TARGET := $(ARCH)-unknown-linux-$(_libc)
+
+#----- Begin Boilerplate
+ifeq (,$(filter _out_%,$(notdir $(CURDIR))))
+  include target.mk
+else
+#----- End Boilerplate
+
+VPATH = $(SRCDIR)
+
 CARGO ?= cargo
 STRIP ?= strip
 CC ?= gcc
 
-RUST_ARCH ?= x86_64
-
 FEATURES := ""#"env_logger"
 
 THIS_DIR := $(dir $(realpath $(lastword $(MAKEFILE_LIST))))
 REPO_ROOT := $(realpath $(THIS_DIR)/..)
-export SERVICEPOINT_HEADER_OUT := $(REPO_ROOT)/include
 
 # TODO: check if override is needed
-override _libc := $(if $(MUSL),musl,gnu)
-override _profile := $(if $(PROFILE),$(PROFILE),release)
-override _rust_cli_profile := $(if $(filter $(_profile),debug),dev,$(_profile))
-override _link_type := $(if $(LINK),$(LINK),dynamic)
+_rust_cli_profile := $(if $(filter $(_profile),debug),dev,$(_profile))
 
-# TODO: make LINK=static fails with linker error "undefined reference to `_dl_find_object'" in libgcc_eh.a
-
-_all_profiles := release debug size-optimized
-ifeq (,$(filter $(_all_profiles),$(_profile)))
-  _profile := $(error "PROFILE has to be set to one of: debug, release, size-optimized")
-endif
+# TODO: `make LINK=static` fails with linker error "undefined reference to `_dl_find_object'" in libgcc_eh.a
 
 STRIPFLAGS += -s --strip-unneeded -R .comment -R .gnu.version -R .note -R .note.gnu.build-id -R .note.ABI-tag
 STATIC_LINK_LIBS += -lservicepoint_binding_c
 
-RUST_TARGET := $(RUST_ARCH)-unknown-linux-$(_libc)
-
 size-optimized_CARGOFLAGS += -Zbuild-std="core,std,alloc,proc_macro,panic_abort" \
 	-Zbuild-std-features="panic_immediate_abort"
 CARGOFLAGS += --manifest-path=$(REPO_ROOT)/Cargo.toml \
@@ -35,7 +50,8 @@ CARGOFLAGS += --manifest-path=$(REPO_ROOT)/Cargo.toml \
 	--no-default-features \
 	--features=$(FEATURES) \
 	--target=$(RUST_TARGET) \
-	$($(_profile)_CARGOFLAGS)
+	$($(_profile)_CARGOFLAGS) \
+	--target-dir=cargo
 
 CFLAGS += -Wall -Wextra -pedantic -fwhole-program -fPIE -pie
 _no_debug_cflags := -ffunction-sections -fdata-sections -Wl,--gc-sections
@@ -53,7 +69,7 @@ size-optimized_CFLAGS += -Oz \
 	-fno-exceptions \
 	$(_no_debug_cflags)
 release_CFLAGS += -O2 \
-    $(_no_debug_cflags)
+	$(_no_debug_cflags)
 debug_CFLAGS += -Og
 static_CFLAGS += -static $(STATIC_LINK_LIBS)
 dynamic_CFLAGS += -Wl,-Bstatic $(STATIC_LINK_LIBS) -Wl,-Bdynamic
@@ -70,16 +86,19 @@ ifneq ($(_profile), debug)
 	RUSTFLAGS += -C link-arg=-s -C link-arg=-Wl,--gc-sections
 endif
 
-CFLAGS += $($(_libc)_CFLAGS) $($(_profile)_CFLAGS) $($(_link_type)_CFLAGS)
+CARGO_OBJDIR := cargo/$(RUST_TARGET)/$(_profile)
+_servicepoint_cflags := -I $(REPO_ROOT)/include -L $(CARGO_OBJDIR)
+
+CFLAGS += $($(_libc)_CFLAGS) $($(_profile)_CFLAGS) $($(_link_type)_CFLAGS) $(_servicepoint_cflags)
 ifeq ($(LTO), 1)
 	CFLAGS += -flto
 endif
 
-RUST_TARGET_DIR := $(REPO_ROOT)/target/$(RUST_TARGET)/$(_profile)
-
-_c_src := $(wildcard ./src/*.c)
+# TODO: wildcard does not work with VPATH
+_c_src := src/announce.c src/brightness_tester.c src/header_logger.c \
+	src/moving_line.c src/random_stuff.c src/wiping_clear.c
 _programs := $(basename $(notdir $(_c_src)))
-_bins := $(addprefix out/, $(_programs))
+_bins := $(_programs)
 _unstripped_bins := $(addsuffix _unstripped, $(_bins))
 _run_programs := $(addprefix run_, $(_programs))
 
@@ -87,42 +106,19 @@ _run_programs := $(addprefix run_, $(_programs))
 
 all: $(_bins)
 
-clean: clean-c clean-rust
-
-clean-c:
-	rm -r out || true
-
-clean-rust:
-	rm $(SERVICEPOINT_HEADER_OUT)/servicepoint.h || true
-	cargo clean
-
 .PHONY: all clean sizes $(_run_programs) clean-c clean-rust build-rust help FORCE
 
-$(_unstripped_bins): out/%_unstripped: src/%.c src/helpers.h build-rust
-	mkdir -p out || true
-	$(CC) $< \
-		-I $(SERVICEPOINT_HEADER_OUT) \
-		-L $(RUST_TARGET_DIR) \
-		$(CFLAGS) \
-		-o $@
+$(_unstripped_bins): %_unstripped: src/%.c src/helpers.h build-rust
+	$(CC) $< $(CFLAGS) -o $@
 
-$(_bins): out/%: out/%_unstripped
+$(_bins): %: %_unstripped
 	$(STRIP) $(STRIPFLAGS) $^ -o $@
 
 build-rust: FORCE
-	mkdir -p $(SERVICEPOINT_HEADER_OUT) || true
 	# generate servicepoint header and library to link against
 	$(CARGO) rustc $(CARGOFLAGS) -- $(RUSTFLAGS)
 
 FORCE: ;
 
-help:
-	@echo "You have the choice of the following parameters:"
-	@echo ""
-	@echo "Variable | Description                       | Default   | Values"
-	@echo "---------+-----------------------------------+-----------+---------------------------"
-	@echo "CARGO    | which cargo binary to use         | 'cargo'   | 'rustup run nightly cargo'"
-	@echo "CC       | which C compiler to use           | 'gcc'     | 'musl-gcc'"
-	@echo "STRIP    | which strip command to use        | 'strip'   | -"
-	@echo "MUSL     | if set, use musl instead of glibc | unset     | '1'"
-	@echo "PROFILE  | Compilation profile               | 'release' | 'debug' or 'size-optimized'"
+#----- Begin Boilerplate
+endif