1. GUN Make
Reference: O’Reilly – Managing Projects with GNU Make 3th.
Eric Hsieh

2. Outline
• Rule
• Variable and macro
• Functions

3. Introduction
• Why do we need GUN Make?
• Source -> Object -> Executable
• Goal: The make program is intended to
automate the mundane aspects of
transforming source code into an executable.
• Base on timestamp.

4. Rule
Target: Prereq1 Prereq2 …
<Tab> commands1
<Tab> commands2
Example:
hello: hello.c
gcc hello.c –o hello

5. Rule
$make
gcc hello.c –o hello
#make again
$make
make: `hello.c’ is up to date.
(1)

6. Rule
Just print
$make - -just-print or –n
Comment character
# gcc hello.c –o hello
(M)

7. Rule
• Default goal
• Top-down (2)

8. Command Modifiers
• @ Do not echo the command. If you want to
apply this modifier to all, you can use the
--silent (or -s) option.
• - The dash prefix indicates that errors in the
command should be ignored by make.
You can use --ignore-errors (or -i) option.
• + The plus modifier tells make to execute the
command even if the --just-print (or -n)
command-line option is given to make.

9. Phony target
Goal: phony target is out of date.
Example:
clean:
rm –rf *.o
$touch clean
$make clean
make: `clean’ is up to date.

10. Phony target
• Remember! Make cannot distinguish the
different between target and phony target. So,
we need define following:
.PHONY: clean
clean:
rm –rf *.o
(2)

11. Standard phony target list

12. Empty target (Cookie)
Example: pl1029 opensource hello
.PHONY: install disclean
$(SOURCE)/.configured:
cd $(SOURCE) && LDFLAGS='-s' CFLAGS='-Os' ./configure
.......
touch $@
install: $(SOURCE)/.configured
make -C $(SOURCE) install-strip
distclean:
make -C $(SOURCE) distclean
rm -f $(SOURCE)/.configured

13. Variable name
• #define
• A = 1234
• CC := cc
• #use
• $A or $(A) or ${A}
• $(CC) or ${CC}

14. Variable name
• Run on Bash
hello:
@echo "Hello, $${USER}" #shell variable USER
@echo "Hello, ${USER}" #make variable USER
or
hello:
@echo "Hello, $$USER" #shell variable USER
@echo "Hello, $(USER)" #make variable USER

15. Automatic variable
• $@ target
• $% archive member,
Example: $@ is foo.a, $% is bar.o
foo.a(bar.o): bar.o
commands…
• $< the first prereq
• $? The names of all prerequisites that
are newer than the target

16. Automatic variable
• $^ The names of all the prerequisites. This list
has duplicate names removed.
• $+ Similar to $^, but it includes duplicates.
• $* The stem of the target filename.
Example: $* is hello
hello.o: hello.c
gcc hello.c –o hello.o
(3)

17. VPATH and vpath
• We can use VPATH or vpath to tell make where to
find the source code.
.
|-- inc
| `-- saydone.h
|-- log
|-- Makefile
`-- src
|-- hello.c
|-- saydone.c

18. VPATH and vpath
• Without VPATH or vpath, we make it and we
will get~
$make
make: *** No rule to make target `hello.c', needed by
`hello.o'. Stop.
• So, we need to tell make where to find source
code by VPATH or vpath.(4)

19. Pattern rule
For example:
hello: hello.o
hello.o: hello.c
$make
cc -c -o hello.o hello.c
cc hello.o -o hello
We need to key “make - -print-data-base” to
understand pattern rule.(5)

20. Dependencies
$ echo "#include <stdio.h>" > stdio.c
$ gcc -M stdio.c
stdio.o: stdio.c /usr/include/stdio.h /usr/include/features.h
/usr/include/bits/predefs.h /usr/include/sys/cdefs.h
/usr/include/bits/wordsize.h /usr/include/gnu/stubs.h
/usr/include/gnu/stubs-32.h
/usr/lib/gcc/i686-linux-gnu/4.4.5/include/stddef.h
/usr/include/bits/types.h /usr/include/bits/typesizes.h
/usr/include/libio.h /usr/include/_G_config.h
/usr/include/wchar.h
/usr/lib/gcc/i686-linux-gnu/4.4.5/include/stdarg.h
/usr/include/bits/stdio_lim.h /usr/include/bits/sys_errlist.h

21. Dependencies
• So, we need to .d and include it.(6)

22. Manager archive library
libsay.a: libsay.a(saydone.o) libsay.a(hello.o)
libsay.a(saydone.o): saydone.o
ar rv $@ $^
libsay.a(hello.o): hello.o
ar rv $@ $^
Same as
libsay.a: saydone.o hello.o
commands…
(8)

23. Assign variable
• Simply expanded variable --- immediately expanded
MAKE_DEPEND := $(CC) –M
• Recursively expanded variable --- lazily expanded
CURRENT_TIME = $(shell date)
• Conditional variable assignment operator
OUTPUT_DIR ?= $(PRERIX)
• Append operator
CPPFLAG += -lpthread

24. When Variables Are Expanded

25. When Variables Are Expanded
• The righthand side of += is expanded
immediately if the lefthand side was originally
defined as a simple variable. Otherwise, its
evaluation is deferred.
• For rules, the targets and prerequisites are
always immediately expanded while the
commands are always deferred.
• (7.1)

26. Macro
• Syntax
define macro-name
commands1
commands2
endef

27. Macro
For example:
define ericEcho
@echo Eric....
@echo $(CC)
@echo $(CPPFLAGS)
endef
#use
$(ericEcho) or $(call ericEcho)

28. Target- and Pattern-Specific Variables
Example:
gui.o: gui.h
$(COMPILE.c) -DUSE_NEW_MALLOC=1 $(OUTPUT_OPTION) $<
or you can do it same as following
gui.o: CPPFLAGS += -DUSE_NEW_MALLOC=1
gui.o: gui.h
#default pattern rule
Another example is libffmpeg.

29. Where Variables Come From
• Command line: (V)
– make CFLAGS=-g CPPFLAGS=‘-DBSD –DDEBUG’
• File:
– by include
• Environment:
– by export or unexport

30. Conditional
• ifdef or ifndef
ifdef RANLIB
$(RANLIB) $@
endif
• ifeq or ifneq
ifeq “$(strip $(OPTIONS))” “-d”
CPPFLAGS += - -DDEBUG
endif
(3)

31. include
• The include directive is used like this:
include definitions.mk
• Special characteristic.
(4)
• If any of the include files is updated by a rule,
make then clears its internal database and
rereads the entire makefile.

32. Standard make Variables
• MAKE_VERSION:
– This is the version number of GNU make.
• CURDIR:
– This variable contains the current working directory of the
executing make process.
• MAKECMDGOALS:
– It contains a list of all the targets specified on the
command line for the current execution of make.
ifneq "$(MAKECMDGOALS)" "clean"
-include $(DEPEND)
Endif
(v)

33. Functions
• $(call macro,parm1 ….)
• $(shell command)
– CURRENT := $(shell date)
• $(filter pattern,text) or $(filter-out pattern,text)
HEADER := $(filter %.h, $(SOURCES))

34. Functions
• $(subst search-string,replace-string,text)
OBJECTS := $(subst .c,.o,$(SOURCES))
• $(patsubst search-pattern,replace-pattern,text)
and $(variable:search=replace)
OBJECTS := $(patsubst %.c,%.o,$(SOURCES))
DEPENDS := $(SOURCES:%.c=%.d)

35. Functions
• $(wildcard pattern…)
SRCS := $(wildcard *.c)
• $(suffix name)
See example
• $(addsuffix suffix,name)
common := $(addsuffix /common.mk,prefix)
#common = prefix/common.mk
• $(error text)

36. Functions
• $(warning text)
• $(strip text)
• $(if condition,true-part,false-part)
PATH_SEP := $(if $(COMSPEC),;,: )