The GNU Make Book

256 Pages·2.701 MB·English

by  John Graham-Cumming

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Technical review
PPRROOBBLLEE MM by Paul Smith,
SSOOLLVVEEDD.. maintainer of GNU make
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GNU make is the most widely used build automation • Handle automatic dependency generation,

tool, but it can be intimidating for new users and rebuilding, and non-recursive make
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its terse language can be tough to parse for even
• Modify the GNU make source and take advantage
experienced programmers. Those who run into dif-
of the GNU Make Standard Library NN
ficulties face a long, involved struggle, often leaving
J O H N G R A H A M - C U M MI NG
unsolved problems behind and GNU make’s vast • Create makefile assertions and debug makefiles
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potential untapped.
GNU make is known for being tricky to use, but it
The GNU Make Book demystifies GNU make and doesn’t have to be. Seasoned users and newbies alike
shows you how to use its best features. You’ll find will find The GNU Make Book to be an indispensable MM
a fast, thorough rundown of the basics of variables, guide to this indispensable tool.
rules, targets, and makefiles. Learn how to fix waste-
AA
fully long build times and other common problems,
ABOUT THE AUTHOR
and gain insight into more advanced capabilities,
KK
John Graham-Cumming is a longtime GNU make
such as complex pattern rules. With this utterly prag-
expert. He wrote the acclaimed machine learning–
matic manual and cookbook, you’ll make rapid
based POPFile email filter and successfully petitioned EE
progress toward becoming a more effective user.
the British government to apologize for its treatment of
You’ll also learn how to:
Alan Turing. He holds a doctorate in computer security
BB
from Oxford University and works at CloudFlare.
• Master user-defined functions, variables, and path
handling
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• Weigh the pitfalls and advantages of GNU make
parallelization OO
KK
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The GNU Make Book
T H e G N U
M a k e B o o k
by John Graham-Cumming
San Francisco
The GNU Make Book. Copyright © 2015 by John Graham-Cumming.
All rights reserved. No part of this work may be reproduced or transmitted in any form or by any means,
electronic or mechanical, including photocopying, recording, or by any information storage or retrieval
system, without the prior written permission of the copyright owner and the publisher.
Printed on demand in USA
ISBN-10: 1-59327-649-4
ISBN-13: 978-1-59327-649-2
Publisher: William Pollock
Production Editor: Alison Law
Cover Illustration: Josh Ellingson
Interior Design: Octopod Studios
Developmental Editors: Greg Poulos and Leslie Shen
Technical Reviewer: Paul Smith
Copyeditor: Anne Marie Walker
Compositor: Susan Glinert Stevens
Proofreader: James Fraleigh
Indexer: Nancy Guenther
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Library of Congress Cataloging-in-Publication Data:
Graham-Cumming, John.
The GNU make book / by John Graham-Cumming. -- 1st edition.
pages cm
Includes index.
Summary: "Covers GNU Make basics through advanced topics, including: user-defined functions,
macros, and path handling; creating makefile assertions and debugging makefiles; parallelization;
automatic dependency generation, rebuilding targets, and non-recursive Make; and using the GNU Make
Standard Library"-- Provided by publisher.
ISBN 978-1-59327-649-2 -- ISBN 1-59327-649-4
1. GNU Emacs. 2. Text editors (Computer programs) 3. Make (Computer file) I. Title.
QA76.76.T49G725 2015
005.13--dc23
2015007254
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about the author
John Graham-Cumming is a longtime GNU make expert. He wrote the
acclaimed machine learning–based POPFile email filter and successfully
petitioned the British government to apologize for its treatment of Alan
Turing. He holds a doctorate in computer security from Oxford University
and works at CloudFlare.
about the Technical Reviewer
Paul Smith has been the Free Software Foundation’s GNU make project
maintainer since 1996. He’s been using and contributing to free software
since the 1980s and to GNU/Linux since 1993. Professionally, he writes
networking and database system software. Personally, he enjoys biking and
scuba diving with his wife and kids.

Brief Contents
Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv
Chapter 1: The Basics Revisited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
Chapter 2: Makefile Debugging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Chapter 3: Building and Rebuilding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .77
Chapter 4: Pitfalls and Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
Chapter 5: Pushing the Envelope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
Chapter 6: The GNU Make Standard Library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225

Contents in De tail
Preface xv
1
The Basics revisiTed 1
Getting Environment Variables into GNU make . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Setting Variables from Outside the Makefile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
The Environment Used by Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
The $(shell) Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Target-Specific and Pattern-Specific Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Target-Specific Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Pattern-Specific Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Version Checking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
MAKE_VERSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
.FEATURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Detecting $(eval) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Using Boolean Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Undefined Variables in Conditionals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Consistent Truth Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Logical Operations Using Boolean Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
User-Defined Logical Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Built-in Logical Operators (GNU make 3 .81 and Later) . . . . . . . . . . . . . . . . . 20
Command Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Delayed Variable Assignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Simple List Manipulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
User-Defined Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
The Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Argument-Handling Gotchas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Calling Built-in Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Recent GNU make Versions: 3 .81, 3 .82, and 4 .0 . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
What’s New in GNU make 3 .81 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
What’s New in GNU make 3 .82 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
What’s New in GNU make 4 .0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
What’s New in GNU make 4 .1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
2
Makefile deBugging 43
Printing the Value of a Makefile Variable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Dumping Every Makefile Variable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Tracing Variable Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Tracing Variable Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
How the Variable Tracer Works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Tracing Rule Execution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
An Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
The SHELL Hack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
An Even Smarter SHELL Hack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
GNU make 4 .0 Tracing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
Makefile Assertions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
assert . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
assert_exists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
assert_target_directory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
An Interactive GNU make Debugger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
The Debugger in Action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
Breakpoints in Patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
Breakpoints in Makefiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
Debugger Internals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
Dynamic Breakpoints in the GNU make Debugger . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
Dynamic Breakpoints in Action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
The Easy Part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
The Trick . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
Rocket Science . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
An Introduction to remake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
Just Print and Trace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
Debugging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
Targets, Macro Values, and Expansion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
3
Building and reBuilding 77
Rebuilding When CPPFLAGS Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
An Example Makefile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
Changing Our Example Makefile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
How Signature Works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
Rebuilding When a File’s Checksum Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
An Example Makefile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
Digesting File Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
The Modified Makefile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
The Hack in Action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
Improving the Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
Automatic Dependency Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
An Example Makefile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
makedepend and make depend . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
Automating makedepend and Removing make depend . . . . . . . . . . . . . . . . . 89
Making Deleted Files Disappear from Dependencies . . . . . . . . . . . . . . . . . . . 90
Doing Away with makedepend . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
Using gcc -MP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
Atomic Rules in GNU make . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
What Not to Do . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
Using Pattern Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
Using a Sentinel File . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
Painless Non-recursive make . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
A Simple Recursive Make . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
A Flexible Non-recursive make System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
Using the Non-recursive make System . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
What About Submodules? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
x Contents in Detail