Makefile介绍

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Motivation

  • Small programs -> single file -> manual compilation

  • "not so small" programs

    • many files
    • multiple components
    • more than one programmers

Motivation - cont.

  • Problems
    • harder to manage
    • every change require long compilation
    • division to components is desired

Motivation - cont.

  • Solution - Makefile

Makefile

  • Makefile describes
    • project structure
    • instructions for files creation
  • A makefile consists of many rules.

Rule syntax

TARGETS: PREREQUISITES

RECIPE

  • In short, each rule describe instructions (RECIPE) to create files (TARGETS) with PREREQUISITES.

  • PREREQUISITES are targets must be created prior to TARGETS.

  • A target is considered old if its modification timestamp is smaller than one of its dependencies's.

Makefile -- cont.

  • TARGETS and PREREQUISITES are file names separated by spaces.

  • Usually there is only one target per rule.

  • TARGETS and PREREQUISITES may contain wildcards, e.g. %.c.

  • Each line of RECIPE starts with a TAB.

  • The first rule indicates the default target (not counting targets that contain wildcards).

make's mechanism

  • make command reads a makefile and records these rules into its data base.

  • GNU Make defaults to search GNUmakefile, makefile, Makefile in order, use the first of these which exists.

  • The first goal (terminology used to refer to the list of targets you specified on the command line) should be created.

  • Prerequisites which appeared in the target must be processed first.

  • This is a recursive process (depth first search).

  • After updating the dependencies , make decides whether it is necessary to recreated the target. This is the case when it is older than one of its dependencies. In the case we recreate the target, execute the associated recipe.

make's mechanism - cont.

  • make virtually construct a dependency DAG (directed acyclic graph).

  • make ensures minimum compilation as long as the project structure is written properly.

  • Do not write something like:

    prog: main.c sum1.c sum2.c

    gcc –o prog main.c sum1.c sum2.c

    which requires compilation of all project when something is changed

Automatic variables

  • $@
  • $^
  • $<
  • others including $, $?, $+, $|, $%, $(%D), %(F), ...

Example

convert: cmdline.o convert.o

g++ $^ -o $@

convert.o: convert.cpp convert.h

g++ -c $<

cmdline.o: cmdline.cpp cmdline.h convert.h

g++ -c $<

Equivalent (implicit rules)

  • make can dedude appropriate recipes according to suffixes

convert: cmdline.o convert.o

convert.o: convert.cpp convert.h

cmdline.o: cmdline.cpp cmdline.h convert.h

Equivalent (implicit rules) - cont.

convert: cmdline.o

convert.o: convert.h

cmdline.o: cmdline.h convert.h

Another example

%.o: %.c

gcc -c $<

Passing parameters

test: FORCE

echo $(VAR)

FORCE:

  • make VAR=hello

  • make VAR=world

Force targets

  • Targets without recipes or prerequisites

Phony targets

  • They do not correspond to real file.

  • Provide some utility, e.g. cleaning intermediate files, archiving the whole project, creating TAGS file for some editors

  • Forced to run its recipe upon executing.

Example

all : prog1 prog2 prog3

.PHONY : all

prog1 : prog1.o utils.o

cc -o prog1 prog1.o utils.o

prog2 : prog2.o

cc -o prog2 prog2.o

prog3 : prog3.o sort.o utils.o

cc -o prog3 prog3.o sort.o utils.o

Practical options of make

  • -n, print the commands to be run but do not execute them

  • -t, touch files instead of running the recipes

  • -B, unconditionally make all targets (overide timestamps)

  • -W file, pretend file has been just modified

  • -p, print the data base that results from reading the makefiles

  • -d, debug mode

  • others, RTFM

Other usage

  • Makefile's mechanism is not limited to programs
    • LaTeX sources
    • website deployment
    • describe any task where some files need updating as a result of changes of other files

Additional features

  • Variables (two flavors: simple and recursive, the latter is also called macros)
  • Functions including string substitution, file name manipulation, foreach, even the the root of evil -- eval
  • VPATH
  • Ability to manipulate archives(.a)
  • Including other makefiles
  • Conditionals
  • Secondary expansion
  • Order-only prerequisites
  • Static patterns
  • Double-colon rules
  • Target/pattern-specific variable values

Acknowledgements

References