Dynamic conditions in makefile - makefile

Question

I maintain a fairly complex makefile for Arduino.
In the makefile, I have target to build *.hex file from *.cpp file. After the *.hex file is generated, I want to check whether the hex size of the file is less than the flash memory of the microcontroller.
To do that, I have added another target called verify_size which touches a *.sizeok file if the hex size is less.
Following is the relevant code
$(TARGET_HEX).sizeok: $(TARGET_HEX)
ifneq ($(strip $(HEX_MAXIMUM_SIZE)),1)
ifeq ($(shell expr `$(call avr_size,$(TARGET_HEX)) | grep Program | awk '{print $$2}'` '<' $(HEX_MAXIMUM_SIZE)), 1)
touch $#
endif
else
#$(ECHO) Maximum Hex size is not specified. Make sure the hex file that you are going to upload is less than microcontrollers flash memory
endif
verify_size: $(TARGET_HEX) $(TARGET_HEX).sizeok
The problem I am facing is that when the makefile is run for the very first time, I get a error saying that the hex file doesn't exist.
After some debugging I found that makefile first goes through the entire file before executing it. When it does this initial pass, the hex file not created yet and therefore the statements which does the parsing of hex file is not executed at all.
Is there a way by which I add dynamic conditions in makefile so that I can find the size of the hex file that was just generated?
Edit:
Based on #beta 's suggestion I changed the code to
$(OBJDIR)/%.hex: $(OBJDIR)/%.elf $(COMMON_DEPS)
$(OBJCOPY) -O ihex -R .eeprom $< $#
#$(ECHO)
$(call avr_size,$<,$#)
ifneq ($(strip $(HEX_MAXIMUM_SIZE)),)
if [ `$(SIZE) $# | awk 'FNR == 2 {print $$2}'` -le $(HEX_MAXIMUM_SIZE) ]; then touch $#.sizeok ; fi
else
#$(ECHO) Maximum Hex size is not specified. Make sure the hex file that you are going to upload is less than microcontrollers flash memory
endif
and it is working. But there is one small issue though.
In the above code, I am using a variable defined in makefile $(SIZE). But when this shell script executes, the value is not replaced. Instead it just replaces it with an empty value.
It works if I hardcode the value, but I am not able to use the value of the variable defined in makefile. Is it possible to access it?
Edit2:
I have posted a separate question for variable expansion issue.

Answer 1

If HEX_MAXIMUM_SIZE hasn't been set, Make should not update the sizeok file, and we shouldn't have a rule that can't actually rebuild its target. And we should update the sizeok file only when we rebuild the hex file. So instead of a rule for $(TARGET_HEX).sizeok, let's just make it a command within the $(TARGET_HEX) rule. (You haven't shown us avr_size, so I can't figure out your method for measuring the size of the hex file, so I'll just use ls and assume you aren't using pathological file names.)
$(TARGET_HEX): %.hex : %.cpps
# Commands to build the target file
if [ `ls -l $# | awk '{print $$5}'` -le $(HEX_MAXIMUM_SIZE) ]; then touch $#.sizeok ; fi
Now we can add a condition, in case HEX_MAXIMUM_SIZE hasn't been set correctly:
$(TARGET_HEX): %.hex : %.cpps
# Commands to build the target file
ifneq ($(strip $(HEX_MAXIMUM_SIZE)),1)
if [ `ls -l $# | awk '{print $$5}'` -le $(HEX_MAXIMUM_SIZE) ]; then touch $#.sizeok
else
#echo Maximum Hex size is not specified. Make sure that $# is small enough for the microcontroller\'s flash memory.
endif
EDIT:
This may take a few iterations. Replace this line:
if [ `$(SIZE) $# | awk 'FNR == 2 {print $$2}'` -le $(HEX_MAXIMUM_SIZE) ]; then touch $#.sizeok ; fi
with this:
$(SIZE) $# | awk 'FNR == 2 {print $$2}'
and tell us the result.