ARM GNU Makefile folder dependency timestamp issue - makefile

Question

I would like to develop a little kernel for my new raspberry pi and used this course : http://www.cl.cam.ac.uk/projects/raspberrypi/tutorials/os/
to understand it. Well when I download a example from this site with more than one source file it compiles the first correctly and then tell me the following: make *** no rule to build target 'build/', needed by 'build/gpio.o'.Stop.
Let me explain. There is a folder sources which contains all source files.In the makefile these files are compiled to .o files in the build folder, but the build folder is ALSO set as dependency when compiling a assembler file. So when the first file is compilied and the build folder created, the folders timestamp is outdated and the second compiling file cant use this directory as a dependency. That is the problem to solve, but I have no idea how.
Here is the makefile:
ARMGNU ?= arm-none-eabi
# The intermediate directory for compiled object files.
BUILD = build/
# The directory in which source files are stored.
SOURCE = source/
# The name of the output file to generate.
TARGET = kernel.img
# The name of the assembler listing file to generate.
LIST = kernel.list
# The name of the map file to generate.
MAP = kernel.map
# The name of the linker script to use.
LINKER = kernel.ld
# The names of all object files that must be generated. Deduced from the
# assembly code files in source.
OBJECTS := $(patsubst $(SOURCE)%.s,$(BUILD)%.o,$(wildcard $(SOURCE)*.s))
# Rule to make everything.
all: $(TARGET) $(LIST)
# Rule to remake everything. Does not include clean.
rebuild: all
# Rule to make the listing file.
$(LIST) : $(BUILD)output.elf
$(ARMGNU)-objdump -d $(BUILD)output.elf > $(LIST)
# Rule to make the image file.
$(TARGET) : $(BUILD)output.elf
$(ARMGNU)-objcopy $(BUILD)output.elf -O binary $(TARGET)
# Rule to make the elf file.
$(BUILD)output.elf : $(OBJECTS) $(LINKER)
$(ARMGNU)-ld --no-undefined $(OBJECTS) -Map $(MAP) -o $(BUILD)output.elf -T $(LINKER)
# Rule to make the object files.
$(BUILD)%.o: $(SOURCE)%.s $(BUILD)
$(ARMGNU)-as -I $(SOURCE) $< -o $#
$(BUILD):
mkdir $#
# Rule to clean files.
clean :
-rm -rf $(BUILD)
-rm -f $(TARGET)
-rm -f $(LIST)
-rm -f $(MAP)
PS::
YEEAAYY I've got it.Are working for that for days but now :)
Look again at the page with this example: `OBJDIR := objdir
OBJS := $(addprefix $(OBJDIR)/,foo.o bar.o baz.o)
$(OBJDIR)/%.o : %.c
$(COMPILE.c) $(OUTPUT_OPTION) $<
all: $(OBJS)
$(OBJS): | $(OBJDIR)
$(OBJDIR):
mkdir $(OBJDIR)`
I just deleted the $(BUILD) folder dependency from the targets and wrote:
$(OBJECTS): | $(BUILD)
So now it works perfect here the few lines I changed:
$(BUILD)%.o: $(SOURCE)%.s
$(ARMGNU)-as -I $(SOURCE) $< -o $#
$(OBJECTS): | $(BUILD)

Answer 1

What you want to do is make $(BUILD) an order-only prerequisite:
$(BUILD)%.o: $(SOURCE)%.s | $(BUILD)