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Introduction To Makefile


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How to use makefiles in building a linux project. Basic level

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Introduction To Makefile

  1. 1. Introduction to Makefile Waqqas Jabbar
  2. 2. Compiling with gcc <ul><li>Compilation and linking in a single step </li></ul><ul><ul><li>gcc file1.c file2.c -o exe </li></ul></ul><ul><li>Compilation and linking in separate steps </li></ul><ul><ul><li>gcc -c file1.c </li></ul></ul><ul><ul><li>gcc -c file2.c </li></ul></ul><ul><ul><li>gcc file1.o file2.o -o exe </li></ul></ul>
  3. 3. “make” command <ul><li>Makefile is the input to “make” command. </li></ul><ul><li>Automate rebuilding software by determining the minimum set of commands that need to be called to do this </li></ul><ul><li>Install program files </li></ul><ul><li>Clean up object files </li></ul><ul><li>Reads a file named “Makefile” in the directory from which it is executed </li></ul>
  4. 4. Makefile syntax <ul><li>Rules </li></ul><ul><ul><li>Target: Dependencies </li></ul></ul><ul><ul><ul><li>(tab) Command </li></ul></ul></ul><ul><ul><ul><li>(tab) Command </li></ul></ul></ul><ul><li>Target </li></ul><ul><ul><li>A file that is generated by a program </li></ul></ul><ul><ul><ul><li>Executable or object files </li></ul></ul></ul><ul><ul><li>The name of an action to carry out </li></ul></ul><ul><li>Dependencies </li></ul><ul><ul><li>Files that are used as inputs to create a Target </li></ul></ul><ul><ul><li>Space separated list </li></ul></ul><ul><ul><li>May include other targets </li></ul></ul>
  5. 5. Makefile syntax <ul><li>Command </li></ul><ul><ul><li>Shell command </li></ul></ul><ul><li>If no target is specified during execution of “make” then the first target is used </li></ul>
  6. 6. Make algorithm <ul><li>Build dependencies </li></ul><ul><ul><li>Determine if dependency is file or action target </li></ul></ul><ul><ul><ul><li>If file by that name exist -> File Target </li></ul></ul></ul><ul><ul><ul><li>Otherwise -> Action Target </li></ul></ul></ul><ul><ul><li>File Target </li></ul></ul><ul><ul><ul><li>Do nothing </li></ul></ul></ul><ul><ul><li>Action Target </li></ul></ul><ul><ul><ul><li>Build target dependencies </li></ul></ul></ul>
  7. 7. Make algorithm <ul><li>Check if at least one of the dependencies is “newer” than the target </li></ul><ul><ul><li>Execute Commands in that rule, if “newer” </li></ul></ul><ul><li>Definition “Newer” </li></ul><ul><ul><li>File Target: </li></ul></ul><ul><ul><ul><li>File Dependency: Check modification times </li></ul></ul></ul><ul><ul><ul><li>Action Dependency:Check commands (in dependency rule) is executed or not </li></ul></ul></ul><ul><ul><li>Action Target: </li></ul></ul><ul><ul><ul><li>File Dependency: Always “newer” </li></ul></ul></ul><ul><ul><ul><li>Action Dependency:Check commands (in dependency rule) is executed or not </li></ul></ul></ul>
  8. 8. Makefile variable <ul><li>Define </li></ul><ul><ul><li>Variable1 = value </li></ul></ul><ul><li>Usage in Commands </li></ul><ul><ul><li>$(Variable1) </li></ul></ul><ul><li>Usage in variables </li></ul><ul><ul><li>Variable2 = $(Variable1) </li></ul></ul><ul><li>Macros </li></ul><ul><ul><li>Variable evaluated when command is executed </li></ul></ul>
  9. 9. Abstract Rules <ul><li>Defines how to build a file `*.s2' from a file `*.s1', where s1 and s2 are suffixes </li></ul><ul><li>.s1.s2: </li></ul><ul><ul><li>(tab) Command </li></ul></ul><ul><ul><li>(tab) Command </li></ul></ul>
  10. 10. Punctuation <ul><li>$<' </li></ul><ul><ul><li>are the dependencies that changed causing the target to need to be rebuilt </li></ul></ul><ul><li>`$@' </li></ul><ul><ul><li>is the target </li></ul></ul><ul><li>`$^' </li></ul><ul><ul><li>are all the dependencies for the current rule </li></ul></ul>
  11. 11. include <ul><li>Include other Makefiles </li></ul><ul><li>Variables can be used </li></ul>
  12. 12. Executing shell command to assign variables <ul><li>$(shell command) </li></ul><ul><ul><li>SVN_VERSION=$(shell if test -d .svn ; then svnversion . | sed -e 's/([1-9]*)([MS])?:?([1-9]*)[MS]?/1/' ; else echo unknown ; fi) </li></ul></ul><ul><ul><li>VERINFO=-DSVN_VERSION=&quot;$(SVN_VERSION)&quot; </li></ul></ul><ul><ul><li>ARCH=$(shell uname -p|sed s/_/' '/|awk '{print $$2}') </li></ul></ul>
  13. 13. Loops in command <ul><li>You can write loops as in shell script </li></ul><ul><ul><li>@for dir in $(SUBDIRS); do </li></ul></ul><ul><ul><ul><li>$(MAKE) -w -C $$dir $(TARGET) clean || exit 1 ; </li></ul></ul></ul><ul><ul><li>done </li></ul></ul>
  14. 14. Wildcard and patsubst <ul><li>SRCS := $(wildcard *.cc) $(wildcard *.c) $(wildcard *.cpp) </li></ul><ul><li>OBJS := $(patsubst, %.o,$(wildcard *.cc)) $(patsubst %.c, %.o,$(wildcard *.c)) $(patsubst %.cpp, %.o,$(wildcard *.cpp)) </li></ul>
  15. 15. Environment variable checking <ul><li>ifeq, else,endif </li></ul><ul><ul><li>ifeq ($(LIB_TYPE), static) </li></ul></ul><ul><ul><ul><li>LIBEXT = a </li></ul></ul></ul><ul><ul><ul><li>COMPILE_LIB = $(AR) -ruv $(TOP)/lib/$(LIBNAME).$(LIBEXT) $(OBJS) </li></ul></ul></ul><ul><ul><li>else </li></ul></ul><ul><ul><ul><li>LIBEXT = so </li></ul></ul></ul><ul><ul><ul><li>COMPILE_LIB = $(CC) -fPIC -shared -Wl,-soname,$(LIBNAME).$(LIBEXT) -o $(TOP)/lib/$(LIBNAME).$(LIBEXT) $(OBJS) $(LIBS) </li></ul></ul></ul><ul><ul><li>endif </li></ul></ul>
  16. 16. Thank you