Basic Make

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A short presentation I gave in 2004 introducing the basic concepts of make

A short presentation I gave in 2004 introducing the basic concepts of make

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Transcript

  • 1. Introduction to Make
      • Alec Clews
      • Victorian Linux Programmers
      • March 2004
  • 2. Building Software
    • Computer programmes can be large and complex.
    • Building is hard to do
      • Takes a long time to rebuild large systems when only small changes made as all files are rebuilt
      • Lots of different related components
      • Arcane syntax required by tools
      • Difficult to repeat reliably
      • Documentation (process, environments, inputs, outputs)
  • 3. Make is
    • An expert system that builds software (or anything else e.g. Docbook)
    • Easy for end users to run
    • Only rebuilds what has changed
    • Understands dependencies between components (files)
    • Documents (??) the process and the outputs
  • 4. How is it used?
    • Build instructions listed in a makefile, with a list of components to be build
      • Default file name is 'makefile'
    • User types make and makefile is processed
    • Usually run in the root of the source/build tree
  • 5. Example
    • Consider a small C program
        • ./inc/fa.h
        • ./inc/fb.h
        • ./src/fa.c
        • ./src/fb.c
        • ./src/proga.c
  • 6. Example makefile
    • bin/proga: obj/proga.o obj/fa.o obj/fb.o
      • -mkdir bin/
      • gcc -o bin/proga obj/proga.o obj/fa.o obj/fb.o
    • obj/proga.o: src/proga.c inc/fa.h inc/fb.h
      • gcc -o obj/proga.o src/proga.c
    • obj/fa.o: src/fa.c inc/fa.h
      • gcc -I ./inc -o obj/fa.o src/fa.c
    • obj/fb.o: src/fb.c inc/fb.h
      • gcc -I ./inc -o obj/fb.o src/fb.c
  • 7. Makefile format
    • Makefile stanzas look like
      • <targetfile>: <dependend files>
      • <tab><shell command to build target>
      • <tab><optionally more commands>
  • 8. Makefile processing
    • Make locates all the dependency (source) files and attempts to locate the target.
      • If the target does not exist or is out of date compared to a dependency then it's rule fires
      • If a dependency does not exist (or is out of date) then make will try and rebuild that first
    • I.E. Make traverses the dependency tree and rebuilds out of date or missing nodes
  • 9. Implicit rules
    • Previous example had lots of identical rules
    • Make supports a generic rule template called an implicit rule
    • If something needs to be built and there is no explicit rule then implicit rules are searched
    • Must use pre-defined macros. e.g. $<, $@ etc.
  • 10. Implicit rule example
    • %.fo: %.dbkx
    • xsltproc --output $@ $(XSLT_FILES) $<
    • I.E. if an fo file is required and a dbkx file is found then run xsltproc and supply target name ($@) as output file and first dependency file as input ($<).
    • Notes: This example is simplified.
    • XSLT_FILE is defined elsewhere in the makefile
  • 11. Makefiles are hard to debug
    • There is no debugger and processing does not follow the makefile in order
    • Use the -p and -d options to dump out (lots) of information for analysis
    • Beware the VPATH directive -- it groups the contents of multiple directories together (concatenates the dependency search path)
  • 12. Java Issues
    • Make has a problem with languages such as Java (also Ada, Delphi ...) where dependencies are calculated by the compiler when doing syntax analysis
    • Use Ant instead (an Ant build.xml file does not list all dependencies, depends on javac)
  • 13. Alternatives to Make
    • The make supplied by your SCM vendor
    • The make supplied by your compiler vendor
    • Cook by Peter Miller, Canberra – Different syntax
    • Apache ANT – Uses an XML build file, very powerful. Consider using instead of make
    • JAM – used by the Boost Project
    • Openmake (costs $) from Catalyst
  • 14. Meta make tools
    • Tools to support the use of Make. Two reasons:
      • Handle the generation of makefile from a simpler list of source files and final targets
      • Handle the porting of makefile between platforms and tool sets.
    • GNU uses autoconf and automake
    • X uses imake (shudder)
    • See also
      • CMAKE
      • OpenMake ($)
  • 15. Further Reading
    • GNU Make manual
    • 'Recursive Make considered Harmful', Peter Miller http://cj5.info/pmiller/books/rmch/
    • 'Building with a Version Control Audit Trail', Alec Clews http://xrl.us/os3df
    • Managing Projects with make, 2nd Edition, publisher O'Reilly (not brilliant, but about the only single topic book on the subject)
    • Many serious *NIX programming books