Ch3 gnu make

GNU Make

3-1
Embedded Linux Course

GNU Make
• make utility determines automatically which
pieces of a large program need to be
recompiled, and issues the commands to
recompile them.
• make examine the source and object files to
determine which source files need to be
recompiled to create new object files.
• You need a file called a Makefile to
tell make what to do

3-2

GNU Make (cont.)
• The relationship of an object file to the source
file used to produce it is known as a dependency
• To determine the dependencies, make reads a
script (Makefile) that defines them
• Makefile tells make how to compile and link a
program

3-3

Makefile
• Essentially a Makefile contains a set of rules used to
build an application
• The first rule seen by make is used as the default rule.
make target
• A rule consists of three parts: the target, its
prerequisites, and the command(s) to perform
target: prereq1 prereq2
target: prereq1 prereq2

<TAB>shell commands
<TAB>shell commands
<TAB>shell commands
<TAB>shell commands
….
….

3-4

A Simple Makefile
edit ::main.o utils.o
edit main.o utils.o
gcc -o edit main.o utils.o
gcc -o edit main.o utils.o

main.o ::main.c defs.h
main.o main.c defs.h
gcc -c main.c
gcc -c main.c
utils.o ::utils.c defs.h
utils.o utils.c defs.h
gcc -c utils.c
gcc -c utils.c

clean ::
clean
rm edit main.o utils.o
rm edit main.o utils.o

3-5

• The target is the file or thing that must be made
• The prerequisites or dependents are those files
that must exist before the target can be
successfully created.
• The commands are just shell commands

foo.o: foo.c foo.h
foo.o: foo.c foo.h

gcc -c foo.c
gcc -c foo.c

3-6

Makefile Syntax
• One or more targets appear to the left of the
colon and zero or more prerequisites can appear
to the right of the colon.
• If no prerequisites are listed to the right, then
only the target(s) that do not exist are updated
target1 target2 target3 : prerequisite1 prerequisite2

<TAB>command1

<TAB>command2

<TAB>command3

3-7

Makefile Syntax (cont.)
• Each command must begin with a tab character.
This (obscure) syntax tells make that the
characters that follow the tab are to be passed to
a subshell for execution.
Makefile2:6: *** missing separator (did you mean TAB instead of 8 spaces?).
Stop.

– Long lines can be continued using the standard Unix escape
character backslash ()
• The comment character for make is the ‘#’

3-8

My First Makefile

• Although the all target has two dependencies, it has no
commands associated with it, but that’s okay because
the only purpose is to force the dependencies to be
satisfied
3-9

Phony Targets
• A phony target is one that is not really the name
of a file. It is just a name for some commands to
be executed when you make an explicit request.
• There are two reasons to use a phony target: to
avoid a conflict with a file of the same name, and
to improve performance.

.PHONY: clean all
.PHONY: clean all
clean:
clean:
rm –rf frammis cooker *.o *.bak *~
rm –rf frammis cooker *.o *.bak *~

3-10

Force Targets
• You can use a target without commands or prerequisites
to mark other targets as phony

clean: FORCE
clean: FORCE
rm $(objects)
rm $(objects)
FORCE:
FORCE:

• If a rule has no prerequisites or commands, and the
target of the rule is a nonexistent file, then make
imagines this target to have been updated whenever its
rule is run. This implies that all targets depending on this
one will always have their commands run.

3-11

Variable
• A macro can be defined in one of three different
ways
CC=gcc
CC=gcc

showmacros:
showmacros:
echo Compiler is $(CC)
echo Compiler is $(CC)
echo HOME is $(HOME)
echo HOME is $(HOME)

export CC=arm-uclibc-gcc
make CC=arm-linux-gcc

3-12

Variable Assignment
• = Variable is a recursively expanded variable
CFLAGS = $(include_dirs) -O
include_dirs = -Ifoo -Ibar
#The following will cause an infinite loop in the variable expansion
CFLAGS = $(CFLAGS) -O
• := Simply expanded variables
     x := foo
     y := $(x) bar
     x := later

is equivalent to

     y := foo bar
     x := later
3-13

Variable Assignment (cont.)
• ?= conditional variable
• it only has an effect if the variable is not yet
defined. This statement:

FOO ?= bar

This is exactly equivalent to this

ifeq (“$(origin FOO)”, “undefined”)
FOO = bar
endif

3-14

Variable Assignment (cont.)
• += add more text to the value of a variable
already defined
objects = main.o foo.o bar.o utils.o
objects += another.o

Using ‘+=’ is similar to

objects = main.o foo.o bar.o utils.o
objects := $(objects) another.o

3-15

Environment Variables
• CC C compiler command
• CFLAGS C compiler flags
• LDFLAGS linker flags, e.g. -L<lib dir> if you have libraries in a
nonstandard directory <lib dir>
• LIBS libraries to pass to the linker, e.g. -l<library>
• CPPFLAGS C/C++/Objective C preprocessor flags, e.g. -I<include dir> if
you have headers in a nonstandard directory <include dir>
• CPP C preprocessor (gcc -E)
• CXX C++ compiler command
• CXXFLAGS C++ compiler flags
• CXXCPP C++ preprocessor

#example
#example
myprog:    $(OBJS)
myprog:    $(OBJS)
        $(CC) -o $@ $^ $(LDFLAGS) $(LIBS)
        $(CC) -o $@ $^ $(LDFLAGS) $(LIBS)

Use these variables to override the choices made by `configure' or to help
Use these variables to override the choices made by `configure' or to help
it to find libraries and programs with nonstandard names/locations.
it to find libraries and programs with nonstandard names/locations.
3-16

Automatic variables
• $@ :The file name of the target of the rule.
• $<  :The name of the first prerequisite.
• $?  :The names of all the prerequisites that are
  newer than the target, with spaces between
them
• $^   :The names of all the prerequisites, with
   spaces between them

libtest.a: foo.o bar.o lose.o win.o
libtest.a: foo.o bar.o lose.o win.o
       $(AR) $(ARFLAGS) $@ $?
       $(AR) $(ARFLAGS) $@ $?

make will pass only those objects files that are newer than the target to ar
3-17

Exercise

3-18

VPATH

3-19

cross.make
# Tool names
# Tool names
CROSS_COMPILE = arm-linux-
CROSS_COMPILE = arm-linux-
AS
AS = $(CROSS_COMPILE)as
= $(CROSS_COMPILE)as
AR
AR = $(CROSS_COMPILE)ar
= $(CROSS_COMPILE)ar
CC
CC = $(CROSS_COMPILE)gcc
= $(CROSS_COMPILE)gcc
CPP
CPP = $(CC) -E
= $(CC) -E
LD
LD = $(CROSS_COMPILE)ld
= $(CROSS_COMPILE)ld
NM
NM = $(CROSS_COMPILE)nm
= $(CROSS_COMPILE)nm
OBJCOPY
OBJCOPY = $(CROSS_COMPILE)objcopy
= $(CROSS_COMPILE)objcopy
OBJDUMP
OBJDUMP = $(CROSS_COMPILE)objdump
= $(CROSS_COMPILE)objdump
RANLIB
RANLIB = $(CROSS_COMPILE)ranlib
= $(CROSS_COMPILE)ranlib
READELF
READELF = $(CROSS_COMPILE)readelf
= $(CROSS_COMPILE)readelf
SIZE
SIZE = $(CROSS_COMPILE)size
= $(CROSS_COMPILE)size
STRINGS
STRINGS = $(CROSS_COMPILE)strings
= $(CROSS_COMPILE)strings
STRIP
STRIP = $(CROSS_COMPILE)strip
= $(CROSS_COMPILE)strip

export AS AR CC CPP LD NM OBJCOPY OBJDUMP RANLIB READELF
export AS AR CC CPP LD NM OBJCOPY OBJDUMP RANLIB READELF
SIZE STRINGS STRIP
SIZE STRINGS STRIP

Note: export these values so that subsequent Makefiles called
Note: export these values so that subsequent Makefiles called
by this Makefile will use the same names
by this Makefile will use the same names 3-20

Recursive Invocations of make

3-21

Top Makfile

$(MAKE) -C $$dir  cd dir && $(MAKE)
MAKEFLAGS += --no-print-directory

3-22

Recursive Invocations of make
(cont.)

/*config.mk*/

3-23

Using command line

3-24

• Note: By declaring the subdirectories as phony
targets (you must do this as the subdirectory
obviously always exists; otherwise it won't be
built)
3-25

Internal Definitions
• For convenience in constructing rules based on
targets and dependencies, it is possible to use
predefined macros and establish implicit rules
that make can use to convert one file type to
another.

3-26

Pattern Rules
• Many programs that read one file type and
output another conform to standard conventions
– .c ==> .o , .S ==> .o
• These conventions allow make to simplify rule
creation by recognizing common filename
patterns and providing built-in rules for
processing them
• The built-in rules are all instances of pattern
rules %.o: %.c
%.o: %.c
# commands to execute (built-in):
$(COMPILE.c) $(OUTPUT_OPTION) $<
$(COMPILE.c) $(OUTPUT_OPTION) $<
OUTPUT_OPTION = -o $@
COMPILE.c = $(CC) $(CFLAGS) $(CPPFLAGS) $(TARGET_ARCH) -c 3-27

Looking at Predefined Rules and Macros
• A large number of implicit rules are built into
make (make -p)
%.o: %.S
%.o: %.S
$(COMPILE.S) -o $@ $<
$(COMPILE.S) -o $@ $<

# there is a special rule to generate a file with no suffix (always an executable)
# there is a special rule to generate a file with no suffix (always an executable)

%: %.o
%: %.o
$(LINK.o) $^ $(LOADLIBES) $(LDLIBS) -o $@
$(LINK.o) $^ $(LOADLIBES) $(LDLIBS) -o $@

%: %.c
%: %.c
$(LINK.c) $^ $(LOADLIBES) $(LDLIBS) -o $@
$(LINK.c) $^ $(LOADLIBES) $(LDLIBS) -o $@
3-28

• The % in a pattern rule is roughly equivalent to *
in a Unix shell
– represents any number of any characters.
• The % can be placed anywhere within the
pattern but can occur only once.
• Characters other than % match literally within a
filename
cooker: cooker.c cooker.h
cooker.o: cooker.c cooker.h
cooker <----- cooker.c
% : %.c
cooker.o <-------- cooker.c
%.o : %.c

3-29

Examples
CC=gcc
CC=gcc
all: frammis cooker
all: frammis cooker

frammis: frammis.c frammis.h
frammis: frammis.c frammis.h

clean:
clean:
rm -rf frammis cooker
rm -rf frammis cooker

%:%.c
%:%.c
echo "$< ===>$@“
echo "$< ===>$@“
$(CC) $(CFLAGS) $< –o $@
$(CC) $(CFLAGS) $< –o $@

3-30

Suffix Rules
CC = gcc
CFLAGS = -g # define a suffix rule for .c -> .o
LD = $(CC) .c.o :
LDFLAGS = $(CC) $(CFLAGS) -c $<
RM = rm
# default target by convention is ``all''
EXE = mainx all : $(EXE)
SRCS = main.c sub1.c sub2.c sub3.c
OBJS = ${SRCS:.c=.o} $(EXE) : $(OBJS)
$(LD) -o $@ $(OBJS)
# list only those we use
.SUFFIXES: .o .c $(OBJS) : proj.h

clean :
-$(RM) -f $(EXE) $(OBJS)

3-31

# Make rules
# Make rules
all: daemon
all: daemon
.PHONY : :install clean distclean
.PHONY install clean distclean
.c.o:
.c.o:
$(CC) $(CFLAGS) $(HEADER_OPS) -c $<
$(CC) $(CFLAGS) $(HEADER_OPS) -c $<

daemon: ${OBJS}
daemon: ${OBJS}
$(CC) -o $(EXEC_NAME) ${OBJS} $(LDFLAGS)
$(CC) -o $(EXEC_NAME) ${OBJS} $(LDFLAGS)
#Copy the executable file into a directory that users typically search for
#Copy the executable file into a directory that users typically search for
##commands;
commands;
install: daemon
install: daemon
test -d $(INSTALL_DIR) ||||$(INSTALL) -d -m 755 $(INSTALL_DIR)
test -d $(INSTALL_DIR) $(INSTALL) -d -m 755 $(INSTALL_DIR)
$(INSTALL) -m 755 $(EXEC_NAME) $(INSTALL_DIR)
$(INSTALL) -m 755 $(EXEC_NAME) $(INSTALL_DIR)

clean:
clean:
rm -f *.o $(EXEC_NAME) core

##distclean might be defined to delete more files than `clean' does.
distclean might be defined to delete more files than `clean' does.
distclean:
distclean:
rm -f *~
rm -f *~
3-32

Built-in Functions
• GNU make has a couple dozen built-in functions
for working with variables and their contents
• $(function-name arg1[, argn])

3-33

$(shell command)
• The shell function accepts a single argument
that is expanded (like all arguments) and passed
to a subshell for execution.
• The standard output of the command is then
read and returned as the value of the function.
Sequences of newlines in the output are
collapsed to a single space. Any trailing newline
is deleted.
• The standard error is not returned, nor is any
program exit status

3-34

Example

3-35

$(wildcard pattern . . . )
sources := $(wildcard *.c *.h)

• The wildcard function accepts a list of patterns
and performs expansion on each one.
• If a pattern does not match any files, the empty
string is returned.
• As with wildcard expansion in targets and
prerequisites, the normal shell globbing
characters are supported: ~, *, ?, [...], and [^...].

3-36

• Another use of wildcard is to test for the
existence of a file in conditionals.
• When used in conjunction with the if function
(described shortly) you often see wildcard
function calls whose argument contains no
wildcard characters at all.

dot-emacs-exists := $(wildcard ~/.emacs)

will return the empty string if the user's home directory
does not contain a .emacs file

3-37

$(subst search-string,replace-string,text)

sources := count_words.c counter.c lexer.c
sources := count_words.c counter.c lexer.c
objects := $(subst .c,.o,$(sources))
objects := $(subst .c,.o,$(sources))

3-38

if-condition
if-condition
text if the condition is true
else
text if the condition is false
endif

• The if-condition can be one of:
ifdef variable-name
ifndef variable-name
ifeq test
ifneq test

3-39

Example

3-40

ifeq (a, a)
# These are equal
endif

ifeq ( “b”, “b” )
# These are not equal - 'b' != 'b '
endif

ifeq "a" "a"
# These are equal
endif

ifeq 'b' 'b'
# So are these
endif

3-41

ifeq (.config,$(wildcard .config))
ifeq (.config,$(wildcard .config))
include .config
include .config
ifeq (.depend,$(wildcard .depend))
ifeq (.depend,$(wildcard .depend))
include .depend
include .depend
ifndef CONFIG_UCLINUX
ifndef CONFIG_UCLINUX
LINUX=vmlinux
LINUX=vmlinux
else
else
LINUX=linux
LINUX=linux
endif
endif
do-it-all:
do-it-all: Version $(LINUX)
Version $(LINUX)
else
else
CONFIGURATION = depend
CONFIGURATION = depend
do-it-all:
do-it-all: depend
depend
endif
endif
else
else
CONFIGURATION = config
CONFIGURATION = config
do-it-all:
do-it-all: config
config
endif
endif

3-42

GNU Build System
(autotools)

3-43

GNU Build System

• The GNU build system (aka, autotools )
provides an environment to a computer
programmer which allows them to write cross-
platform software
• It also makes the build process easier on the
user, allowing the user to usually just run a
small set of commands to build the program
from its source code and install it.

3-44

GNU Autotools
• Autotools comprises the GNU utility programs
Autoconf, Automake, and Libtool.
• Other related tools frequently used with the GNU
build system are GNU’s make, GNU gettext,
pkg-config, and the GNU gcc.
• The utilities used by the GNU build system are
only required to be on the developer’s
workstation

3-45

autoconf
and * * *
automake

*

*

*
a. * means executable
b. template file, customarily ending in ".in“, “ac”

3-46

GNU Autoconf
• Autoconf is a tool for producing shell scripts that
automatically configure software source code
packages to adapt to many kinds of UNIX-like
systems.
• Autoconf makes use of GNU m4 to transform a
user-written 'configure.ac' file to a portable
'configure‘ script.
• The 'configure' generates customized headers
and makefiles derived from pre-written
templates.

3-47

GNU Autoconf (cont.)
• The Autoconf approach to portability is to test
whether a particular feature is supported or not
• it also allows user to have the ‘configure’ script
to customize.

3-48

GNU Automake
• Automake aims to allow the programmer to write
a makefile in a higher-level language, rather
than having to write the whole makefile manually
• Automake helps to create portable Makefile,
which are in turn processed with the make utility.
• Must be used with GNU autoconf

3-49

GNU Automake (cont.)
• Automake contains two commands:
– aclocal : a program for autoconf users
– Automake
• In simple cases, it suffices to give:
– a line that declares the name of the program to build
– a list of source files
– a list of command-line options to be passed to the gcc (namely,
in which directories header files will be found)
– a list of command-line options to be passed to the ld (which
libraries the program needs and in what directories they are to
be found).

3-50

GNU Libtool
• Libtool helps manage the creation of static and
dynamic libraries on various Unix-like operating
systems.
• Libtool accomplishes this by abstracting the
library creation process, hiding differences
between various systems

3-51

ScreenShot for CodeBlocks
Free IDE ,e.g.,
• Eclipse
• Anjuta
• CodeBlocks

3-52

Configure Script
• ‘configure’ attempts to guess correct values for various
system-dependent variables used during compilation.
It uses those values to create a `Makefile' in each
directory of the package.
• It may also create one or more `.h' files containing
system-dependent definitions.

In new development, library dependency checking has been done in great
part using pkg-config

pkg-config is a helper tool used when compiling applications and libraries. It
helps you insert the correct compiler options on the command line.

3-53

Screenshot for ‘./configure’

3-54

The Output from ‘configure’
• A script config.status that you can run in the
future to recreate the current configuration
• A file config.cache that saves the results of its
tests to speed up reconfiguring, and
• A file config.log containing compiler output,
useful for debugging `configure‘

make distclean
make realclean
remove the files that `configure' created (so you can compile the
package for a different kind of computer),

3-55

• If you need to do unusual things to compile the
package, please try to figure out how `configure'
could check whether to do them
• If at some point config.cache contains results
you don't want to keep, you may remove or edit
it.
• You only need configure.ac if you want to
change it or regenerate `configure' using a
newer version of autoconf.

3-56

Compilers and Options
• Some systems require unusual options for
compilation or linking that the `configure' script
does not know about
CC=c89 CFLAGS=-O2 LIBS=-lposix ./configure
CPPFLAGS=-I/usr/local/include LDFLAGS=-s ./configure

• The 'configure' script can be given a number of
options to enable and disable various features.
For a complete list, type:
./configure --help

3-57

Specifying the System Type
• There may be some features `configure' can not figure
out automatically, but needs to determine by the type of
host the package will run on

System types:
--build=BUILD configure for building on BUILD [guessed]
--host=HOST cross-compile to build programs to run on
HOST [BUILD]
– type format: CPU-OS
– See the file `config.sub' for the possible values of each field .

• If you are building compiler tools for cross-compiling, you
can will need –host=CPU-OS

3-58

Screenshot

3-59

Examples for configure
Step1 : Export your toolchain path firstly
– export PATH=/usr/local/arm/3.4.1/bin:$PATH

Step 2 : Execute configure script,
– CC=arm-linux-gcc ./configure --host=arm-linux
– CC=mips-uclibc-gcc ./configure --host=mips-linux
– CC=arm-elf-gcc ./configure --target=arm-linux --endian-mode=littile

Normally, you will need to execute “./configure - - help” to enable or disable
some features supported by this software package

3-60

Cross-compiling Applications
“CC=arm-linux-gcc ./configure –host=arm-linux ”

Unluckily enough, you need to go through the following..
Step 1: “./configure”

this will create a Makefile for your x86 linux.

Step 2: include <SDK>/filesystem/make.def

Include make.def at the top of your Makefile

Step 3: Edit Makefile appropriately
For example,
# CC=gcc
# AR=ar
-I<the_path_to_your_toolchain_include_path>
-L<the_path_to_your_toolchain_library_path>

3-61

Test Your Program
Download your code to board for testing
• Ifconfig eth0 192.168.2.x
• cd /var;
• tftp –g –r <executable> <tftp_server>
• chmod +x <executable>
• ./ <executable>

3-62

Faild to configure

3-63

Cross-compiling Kernel modules
• Building the kernel module will need the properly
configured kernel sources
• During the build process of this package the
kernel Makefile and the current kernel
configuration will be used
• The modules should be compiled with the same
compiler version.
Some kernel modules are only supported with recent kernel versions. That
means that compilation of these drivers might fail with older kernel versions.

3-64

Kernel Source Layout

3-65

#rules.make

KERNELSRC:= linux-2.6.x

export KERNELSRC

3-66

Test Your Module
Download led.ko and test program to your board
# 設定板子 IP # 載入 Module
Ifconfig eth0 192.168.2.x insmod led.ko
cd /var; # 查詢 Module
# 取得 led.ko lsmod
tftp –g –r led.ko <tftp_server> # 產生 device node
# 取得測試程式 mknod /dev/led c 230 0
tftp –g –r led_test <tftp_server> # 執行測試程式
# 測試程式加上執行權限 ./led_test
chmod +x led_test # 移除 Module
rmmod led

3-67

References
• GNU Manuals Online
– http://www.gnu.org/software/make/manual/
– Managing Projects with GNU Make” by Robert
Mecklenburg
– O'Reilly, Nov 19, 2004

3-68

Ch3 gnu make

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