title: Need help understanding Makefile in xv6
body: <p>I have been reading the makefile of xv6 project. I want to put all the user programs into a folder to keep the project tidy. I can not find where it compiles the user programs. I know that when i run: make fs.img; it will compile the user programs, but i can not find any commands to do so. I also want all the kernel code to go into a directory called &quot;kernel&quot;.<br />
  Is there a feature in make that allows automatic compilation or is there just something I'm not seeing. And could anyone suggest any make docs to help me understand this makefile.</p>
  <p>My Makefile:</p>
  <pre><code>OBJS = \
      bio.o\
      console.o\
      exec.o\
      file.o\
      fs.o\
      ide.o\
      ioapic.o\
      kalloc.o\
      kbd.o\
      lapic.o\
      log.o\
      main.o\
      mp.o\
      picirq.o\
      pipe.o\
      proc.o\
      sleeplock.o\
      spinlock.o\
      string.o\
      swtch.o\
      syscall.o\
      sysfile.o\
      sysproc.o\
      trapasm.o\
      trap.o\
      uart.o\
      vectors.o\
      vm.o\
  
  # Cross-compiling (e.g., on Mac OS X)
  # TOOLPREFIX = i386-jos-elf
  
  # Using native tools (e.g., on X86 Linux)
  #TOOLPREFIX = 
  
  # Try to infer the correct TOOLPREFIX if not set
  ifndef TOOLPREFIX
  TOOLPREFIX := $(shell if i386-jos-elf-objdump -i 2&gt;&amp;1 | grep '^elf32-i386$$' &gt;/dev/null 2&gt;&amp;1; \
      then echo 'i386-jos-elf-'; \
      elif objdump -i 2&gt;&amp;1 | grep 'elf32-i386' &gt;/dev/null 2&gt;&amp;1; \
      then echo ''; \
      else echo &quot;***&quot; 1&gt;&amp;2; \
      echo &quot;*** Error: Couldn't find an i386-*-elf version of GCC/binutils.&quot; 1&gt;&amp;2; \
      echo &quot;*** Is the directory with i386-jos-elf-gcc in your PATH?&quot; 1&gt;&amp;2; \
      echo &quot;*** If your i386-*-elf toolchain is installed with a command&quot; 1&gt;&amp;2; \
      echo &quot;*** prefix other than 'i386-jos-elf-', set your TOOLPREFIX&quot; 1&gt;&amp;2; \
      echo &quot;*** environment variable to that prefix and run 'make' again.&quot; 1&gt;&amp;2; \
      echo &quot;*** To turn off this error, run 'gmake TOOLPREFIX= ...'.&quot; 1&gt;&amp;2; \
      echo &quot;***&quot; 1&gt;&amp;2; exit 1; fi)
  endif
  
  # If the makefile can't find QEMU, specify its path here
  # QEMU = qemu-system-i386
  
  # Try to infer the correct QEMU
  ifndef QEMU
  QEMU = $(shell if which qemu &gt; /dev/null; \
      then echo qemu; exit; \
      elif which qemu-system-i386 &gt; /dev/null; \
      then echo qemu-system-i386; exit; \
      elif which qemu-system-x86_64 &gt; /dev/null; \
      then echo qemu-system-x86_64; exit; \
      else \
      qemu=/Applications/Q.app/Contents/MacOS/i386-softmmu.app/Contents/MacOS/i386-softmmu; \
      if test -x $$qemu; then echo $$qemu; exit; fi; fi; \
      echo &quot;***&quot; 1&gt;&amp;2; \
      echo &quot;*** Error: Couldn't find a working QEMU executable.&quot; 1&gt;&amp;2; \
      echo &quot;*** Is the directory containing the qemu binary in your PATH&quot; 1&gt;&amp;2; \
      echo &quot;*** or have you tried setting the QEMU variable in Makefile?&quot; 1&gt;&amp;2; \
      echo &quot;***&quot; 1&gt;&amp;2; exit 1)
  endif
  
  CC = $(TOOLPREFIX)gcc
  AS = $(TOOLPREFIX)gas
  LD = $(TOOLPREFIX)ld
  OBJCOPY = $(TOOLPREFIX)objcopy
  OBJDUMP = $(TOOLPREFIX)objdump
  CFLAGS = -fno-pic -static -fno-builtin -fno-strict-aliasing -O2 -Wall -MD -ggdb -m32 -Werror -fno-omit-frame-pointer
  CFLAGS += $(shell $(CC) -fno-stack-protector -E -x c /dev/null &gt;/dev/null 2&gt;&amp;1 &amp;&amp; echo -fno-stack-protector)
  ASFLAGS = -m32 -gdwarf-2 -Wa,-divide
  # FreeBSD ld wants ``elf_i386_fbsd''
  LDFLAGS += -m $(shell $(LD) -V | grep elf_i386 2&gt;/dev/null | head -n 1)
  
  # Disable PIE when possible (for Ubuntu 16.10 toolchain)
  ifneq ($(shell $(CC) -dumpspecs 2&gt;/dev/null | grep -e '[^f]no-pie'),)
  CFLAGS += -fno-pie -no-pie
  endif
  ifneq ($(shell $(CC) -dumpspecs 2&gt;/dev/null | grep -e '[^f]nopie'),)
  CFLAGS += -fno-pie -nopie
  endif
  
  xv6.img: bootblock kernel
      dd if=/dev/zero of=xv6.img count=10000
      dd if=bootblock of=xv6.img conv=notrunc
      dd if=kernel of=xv6.img seek=1 conv=notrunc
  #
  xv6memfs.img: bootblock kernelmemfs
      dd if=/dev/zero of=xv6memfs.img count=10000
      dd if=bootblock of=xv6memfs.img conv=notrunc
      dd if=kernelmemfs of=xv6memfs.img seek=1 conv=notrunc
  #
  bootblock: bootasm.S bootmain.c
      $(CC) $(CFLAGS) -fno-pic -O -nostdinc -I. -c bootmain.c
      $(CC) $(CFLAGS) -fno-pic -nostdinc -I. -c bootasm.S
      $(LD) $(LDFLAGS) -N -e start -Ttext 0x7C00 -o bootblock.o bootasm.o bootmain.o
      $(OBJDUMP) -S bootblock.o &gt; bootblock.asm
      $(OBJCOPY) -S -O binary -j .text bootblock.o bootblock
      ./sign.pl bootblock
  #
  entryother: entryother.S
      $(CC) $(CFLAGS) -fno-pic -nostdinc -I. -c entryother.S
      $(LD) $(LDFLAGS) -N -e start -Ttext 0x7000 -o bootblockother.o entryother.o
      $(OBJCOPY) -S -O binary -j .text bootblockother.o entryother
      $(OBJDUMP) -S bootblockother.o &gt; entryother.asm
  #
  initcode: initcode.S
      $(CC) $(CFLAGS) -nostdinc -I. -c initcode.S
      $(LD) $(LDFLAGS) -N -e start -Ttext 0 -o initcode.out initcode.o
      $(OBJCOPY) -S -O binary initcode.out initcode
      $(OBJDUMP) -S initcode.o &gt; initcode.asm
  
  kernel: $(OBJS) entry.o entryother initcode kernel.ld
      $(LD) $(LDFLAGS) -T kernel.ld -o kernel entry.o $(OBJS) -b binary initcode entryother
      $(OBJDUMP) -S kernel &gt; kernel.asm
      $(OBJDUMP) -t kernel | sed '1,/SYMBOL TABLE/d; s/ .* / /; /^$$/d' &gt; kernel.sym
  
  # kernelmemfs is a copy of kernel that maintains the
  # disk image in memory instead of writing to a disk.
  # This is not so useful for testing persistent storage or
  # exploring disk buffering implementations, but it is
  # great for testing the kernel on real hardware without
  # needing a scratch disk.
  
  #MEMFSOBJS = $(filter-out ide.o,$(OBJS)) memide.o
  #kernelmemfs: $(MEMFSOBJS) entry.o entryother initcode kernel.ld fs.img
  #   $(LD) $(LDFLAGS) -T kernel.ld -o kernelmemfs entry.o  $(MEMFSOBJS) -b binary initcode entryother fs.img
  #   $(OBJDUMP) -S kernelmemfs &gt; kernelmemfs.asm
  #   $(OBJDUMP) -t kernelmemfs | sed '1,/SYMBOL TABLE/d; s/ .* / /; /^$$/d' &gt; kernelmemfs.sym
  #
  #tags: $(OBJS) entryother.S _init
  #   etags *.S *.c
  
  vectors.S: vectors.pl
      ./vectors.pl &gt; vectors.S
  
  ULIB = ulib.o usys.o printf.o umalloc.o
  
  #
  _%: %.o $(ULIB)
      $(LD) $(LDFLAGS) -N -e main -Ttext 0 -o $@ $^
      $(OBJDUMP) -S $@ &gt; $*.asm
      $(OBJDUMP) -t $@ | sed '1,/SYMBOL TABLE/d; s/ .* / /; /^$$/d' &gt; $*.sym
  
  _forktest: forktest.o $(ULIB)
      # forktest has less library code linked in - needs to be small
      # in order to be able to max out the proc table.
      $(LD) $(LDFLAGS) -N -e main -Ttext 0 -o _forktest forktest.o ulib.o usys.o
      $(OBJDUMP) -S _forktest &gt; forktest.asm
  
  mkfs: mkfs.c fs.h
      gcc -Werror -Wall -o mkfs mkfs.c
  
  # Prevent deletion of intermediate files, e.g. cat.o, after first build, so
  # that disk image changes after first build are persistent until clean.  More
  # details:
  # http://www.gnu.org/software/make/manual/html_node/Chained-Rules.html
  .PRECIOUS: %.o
  
  UPROGS=\
      _cat\
      _echo\
      _forktest\
      _grep\
      _init\
      _kill\
      _ln\
      _ls\
      _mkdir\
      _rm\
      _sh\
      _stressfs\
      _usertests\
      _wc\
      _zombie\
      _login\
      _cp\
      _head\
      _bedit\
      _clear\
      _tail\
      _sleep\
      _date\
  
  
  fs.img: mkfs README $(UPROGS)
      ./mkfs fs.img README $(UPROGS) simple.txt
  
  -include *.d
  
  clean: 
      rm -f *.tex *.dvi *.idx *.aux *.log *.ind *.ilg \
      *.o *.d *.asm *.sym vectors.S bootblock entryother \
      initcode initcode.out kernel xv6.img fs.img kernelmemfs \
      xv6memfs.img mkfs .gdbinit \
      $(UPROGS)
  
  # make a printout
  FILES = $(shell grep -v '^\#' runoff.list)
  PRINT = runoff.list runoff.spec README toc.hdr toc.ftr $(FILES)
  
  #xv6.pdf: $(PRINT)
  #   ./runoff
  #   ls -l xv6.pdf
  
  #print: xv6.pdf
  
  # run in emulators
  
  #bochs : fs.img xv6.img
  #   if [ ! -e .bochsrc ]; then ln -s dot-bochsrc .bochsrc; fi
  #   bochs -q
  
  # try to generate a unique GDB port
  GDBPORT = $(shell expr `id -u` % 5000 + 25000)
  # QEMU's gdb stub command line changed in 0.11
  QEMUGDB = $(shell if $(QEMU) -help | grep -q '^-gdb'; \
      then echo &quot;-gdb tcp::$(GDBPORT)&quot;; \
      else echo &quot;-s -p $(GDBPORT)&quot;; fi)
  ifndef CPUS
  CPUS := 2
  endif
  QEMUOPTS = -drive file=fs.img,index=1,media=disk,format=raw -drive file=xv6.img,index=0,media=disk,format=raw -smp $(CPUS) -m 512 $(QEMUEXTRA)
  
  qemu: fs.img xv6.img
      $(QEMU) -serial mon:stdio $(QEMUOPTS)
  
  #qemu-memfs: xv6memfs.img
  #   $(QEMU) -drive file=xv6memfs.img,index=0,media=disk,format=raw -smp $(CPUS) -m 256
  
  #qemu-nox: fs.img xv6.img
  #   $(QEMU) -nographic $(QEMUOPTS)
  
  #.gdbinit: .gdbinit.tmpl
  #   sed &quot;s/localhost:1234/localhost:$(GDBPORT)/&quot; &lt; $^ &gt; $@
  
  #qemu-gdb: fs.img xv6.img .gdbinit
  #   @echo &quot;*** Now run 'gdb'.&quot; 1&gt;&amp;2
  #   $(QEMU) -serial mon:stdio $(QEMUOPTS) -S $(QEMUGDB)
  
  #qemu-nox-gdb: fs.img xv6.img .gdbinit
  #   @echo &quot;*** Now run 'gdb'.&quot; 1&gt;&amp;2
  #   $(QEMU) -nographic $(QEMUOPTS) -S $(QEMUGDB)
  
  # CUT HERE
  # prepare dist for students
  # after running make dist, probably want to
  # rename it to rev0 or rev1 or so on and then
  # check in that version.
  
  EXTRA=\
      mkfs.c ulib.c user.h cat.c echo.c forktest.c grep.c kill.c\
      ln.c ls.c mkdir.c rm.c stressfs.c usertests.c wc.c zombie.c\
      printf.c umalloc.c\
      README dot-bochsrc *.pl toc.* runoff runoff1 runoff.list\
      .gdbinit.tmpl gdbutil\
  
  dist:
      rm -rf dist
      mkdir dist
      for i in $(FILES); \
      do \
          grep -v PAGEBREAK $$i &gt;dist/$$i; \
      done
      sed '/CUT HERE/,$$d' Makefile &gt;dist/Makefile
      echo &gt;dist/runoff.spec
      cp $(EXTRA) dist
  
  dist-test:
      rm -rf dist
      make dist
      rm -rf dist-test
      mkdir dist-test
      cp dist/* dist-test
      cd dist-test; $(MAKE) print
      cd dist-test; $(MAKE) bochs || true
      cd dist-test; $(MAKE) qemu
  
  # update this rule (change rev#) when it is time to
  # make a new revision.
  #tar:
  #   rm -rf /tmp/xv6
  #   mkdir -p /tmp/xv6
  #   cp dist/* dist/.gdbinit.tmpl /tmp/xv6
  #   (cd /tmp; tar cf - xv6) | gzip &gt;xv6-rev10.tar.gz  # the next one will be 10 (9/17)
  #
  
  .PHONY: dist-test dist
  </code></pre>
  <p>Edit:
  what I want to do is put all my UPROGS programs into a directory called programs. How would i change the makefile to do so.</p>