CC=gcc
CFLAGS=-lm

ODIR=obj
BINDIR=bin

HOST_OS   := $(shell uname -s 2>/dev/null | tr "[:upper:]" "[:lower:]")
TARGET_OS ?= $(HOST_OS)

HOST_ARCH   := $(shell uname -m)
TARGET_ARCH ?= $(HOST_ARCH)

ifeq ($(TARGET_ARCH),x86_64)
    TARGET_ARCH = amd64
endif

all: $(BINDIR)/helloworld-$(TARGET_OS)-$(TARGET_ARCH)

$(ODIR)/%.o: %.c
	mkdir -p $(ODIR)
	$(CC) -c -o $@ $^ $(CFLAGS)

$(BINDIR)/%-$(TARGET_OS)-$(TARGET_ARCH): $(ODIR)/%.o
	mkdir -p $(BINDIR)
	$(CC) -o $@ $^ $(CFLAGS)

clean:
	rm -rf $(ODIR) $(BINDIR)