Lab46 Wiki

Typical configurations for makefiles.

Note: The code below are just examples, you must modify them to work with your own software.

Makefile component identification.

• # - comments
• \ - splits long lines
• tab - required after depenancy lines (ie: [target : dependancy], enter, tab over)
• $() or ${} - both work as variable identifiers

gcc main.c file1.c file2.c -o hello

The above is what you normally would run to compile a program with the gcc compiler and the 3 .c file to an executable called hello.

#
# Makefile for hello 
#
# compiler: gcc
# to compile type "make" at command line
#
all :
      gcc main.c file1.c file2.c -o hello

This file is saved with the name “Makefile”. It will compile the program hello, but without typing the entire gcc line out on the command line.

Things to note - [target]:[dependencies] in this case, the target “all” depends on everything. This looks for time stamps to save on compile time. If a dependent has a newer last changed stamp then the target then the target needs to be recompiled else is left alone.

#
# Makefile for hello 
#
# compiler: gcc
# to compile type "make" at command line
#
all : hello
 
hello : main.o file1.o file2.o
      gcc main.o file1.o file2.o -o hello
 
main.o : main.c
      echo main.c is being compiled 
      gcc -c main.c
 
file1.o : file1.c
      echo file1.c is being compiled 
      gcc -c file1.c
 
file2.o : file2.c
      echo file2.c is being compiled
      gcc -c file2.c
 
clean : 
      rm -rf *.o hello

This example builds a little on what was there before. last time if there was a change to one of the files everything was recompiled. breaking everything up as shown here if only file2.c was modified on file2 would be recompiled. the clean: removes any left over executable and object files. I have also thrown in some simple echos to show that shell commands can be used as well.

#
# Makefile for hello 
#
# compiler: gcc
# to compile type "make" at command line
#
 
CC = gcc
CFLAGS = -c
OBJ = main.o file1.o file2.o
 
all : hello
 
hello : $(OBJ)
      $(CC) $(OBJ) -o hello
 
main.o : main.c
      echo main.c is being compiled 
      $(CC) $(CFLAGS) main.c
 
file1.o : file1.c
      echo file1.c is being compiled 
      $(CC) $(CFLAGS) main.c
 
file2.o : file2.c
      echo file2.c is being compiled
      $(CC) $(CFLAGS) file2.c
 
clean : 
      rm -rf *.o hello

In this version of the makefile I have added variables for everything that is repeated throughout the file. If you then wanted to change lets say the compiler all i would have to do is change the CC value at the top.

asm Makefile An example of a make file for use in assembly language.

#
# Makefile for asm
# name: Makefile
# to run "make" at cli
# 
 
CC = gcc
CC2 = nasm
PROG = first
OBJ = driver.c asm_io.o first.o
CFLAGS = -f elf -d ELF_TYPE
 
$(PROG) : $(OBJ)
      $(CC) $(OBJ) -o $(PROG)
 
asm_io.o :
      $(CC2) $(CFLAGS) asm_io.o
 
$(PROG).o : $(PROG).asm
      $(CC2) $(CFLAGS) $(PROG).asm

• GNU Make - documentation