A make file:

BIT = 32  # could override in commandline

ARCH_PLATFORM:sh = /usr/bin/uname -p  # invokes sh cmd: output:sparc
ARCH_sparc       = sparc-$BIT
ARCH_DIR         = $(ARCH_$(ARCH_PLATFORM)) # Two macros nesting OK.
RELEASE:sh        = /usr/bin/uname -r | sed 's/^5/2/' | cut -d\. -f1,2

opt       :=   VARIANT = opt
clean-opt :=   VARIANT = clean-opt # Assign macros depending on target
%.i       :=   VARIANT = cpp   # If the target is any file.i

bits64 := OBJ_DEST_DIR  = sparcv9
bits32 := OBJ_DEST_DIR  = .

# use TOP_DIR or WS_ROOT or VTS_BASE

# the individual make files provide these as follows:
SOURCE = a.c b.c c.c
BINARY = a.out

TARG = $(BIN)

# The macros manipulate this as follows:
OBJS  = $(SOURCE:%.c=$(OBJ_DEST_DIR)/%.o)
BIN   = $(BINARY:%=$(OBJ_DEST_DIR)/%)

$(BIN) : $$(OBJS)
	# The rule of making binary goes here...

# You can say a set of .o files could be compiled from local .c file:
sparcv9/%.o ./%.o : %.c
	$(CC) -c $< -o $@

sparcv9/a.o ./b.o : %.c   # This will fail. The target should have %
	$(CC) -c $< -o $@

OBJ_FORM = sparcv9/%.o ./%.o

$(OBJ_FORM) : %.c
	$(CC)  -c $< -o $@
#

OBJ = $(SOURCE:.c=.o) # replaces the suffix
OBJ = $(SOURCE:%.c=sparcv9/%.o) # produces sparcv9/a.o, etc. 

DIRS = opt/sparcv9 debug/sparcv9
BIN_TARGS.c = $(DIRS:%=%/bin/$(BINARY.c)) #what does this mean ?