Re: someone make me understand make please

[Paul Smith]

On Sun, 2007-08-05 at 21:35 +0100, Martin Knappe wrote:
> To be honest, I've tried so many combinations of $, `` and stuff that I 
> just didn't know which of all the version (that didn't work out) I 
> should have posted :-) They all had different bugs..
> Yeah, sorry, 512.bin depends on boot.bin, not on boot.bin.bin (typo)
> Couldnt you just tell me how YOU would write the Makefile to do what I 
> want so I can see clearer ,please?

Please reply to the list, not to me privately: if you send it to the
list others besides me can help, plus other people reading the archives
can see the entire thread.

This is how I would write it:

        # How we compute the size of the boot file
        BOOT_SIZE = `stat -c %s boot.bin`
        
        512.bin: 512.asm Makefile boot.bin
                -rm $@
                BOOT_SIZE=$(BOOT_SIZE) nasm -f bin $< -o $@
        
        boot.bin: main.o video.o utilities.o Makefile
                ld $(filter %.o,$^) -e start -N -M > boot.mem -o $@ --oformat 
binary -T script
                ndisasm -b 32 $@ > boot.ndisasm
                size=$(BOOT_SIZE); blocks=`expr $$size / 512`; \
                        dd if=/dev/null of=gdt.bin seek=`expr $$blocks + 1` 
count=1

If you know for a fact that your /bin/sh will be POSIX compliant, and
will grok the POSIX $(...) alternative to ``, then you can simplify
things a bit:

        # How we compute the size of the boot file
        BOOT_SIZE = $$(stat -c %s boot.bin)
        
        512.bin: 512.asm Makefile boot.bin
                -rm $@
                BOOT_SIZE=$(BOOT_SIZE) nasm -f bin $< -o $@
        
        boot.bin: main.o video.o utilities.o Makefile
                ld $(filter %.o,$^) -e start -N -M > boot.mem -o $@ --oformat 
binary -T script
                ndisasm -b 32 $@ > boot.ndisasm
                dd if=/dev/null of=gdt.bin seek=$$(expr $$(expr $(BOOT_SIZE) / 
512) + 1) count=1

And, if you know that your /bin/sh will be a POSIX shell, and will grok
the POSIX $(( ... )) math expression, you can do even better:

        # How we compute the size of the boot file
        BOOT_SIZE = $$(stat -c %s boot.bin)
        
        512.bin: 512.asm Makefile boot.bin
                -rm $@
                BOOT_SIZE=$(BOOT_SIZE) nasm -f bin $< -o $@
        
        boot.bin: main.o video.o utilities.o Makefile
                ld $(filter %.o,$^) -e start -N -M > boot.mem -o $@ --oformat 
binary -T script
                ndisasm -b 32 $@ > boot.ndisasm
                dd if=/dev/null of=gdt.bin seek=$$(( ($(BOOT_SIZE) / 512) + 1 
)) count=1

-- 
-------------------------------------------------------------------------------
 Paul D. Smith <address@hidden>          Find some GNU make tips at:
 http://www.gnu.org                      http://make.paulandlesley.org
 "Please remain calm...I may be mad, but I am a professional." --Mad Scientist