The Linux Development Platform Configuring, Using, and ... - Classes

CH04.fm Page 117 Monday, October 7, 2002 8:54 PM
The make Rules 117
The same process is repeated for the dnsresolver and the following two lines are displayed:
gcc -g -O2 -c dnsresolver.c
gcc -static dnsresolver.o common.o -o dnsresolver
After building dnsresolver, nothing is left in the default target rule “all,” so make will
stop at this point.
Now let us see what happens if you modify the ftp.h file and run make again. The output
will be as follows:
[root@rr2 test]# make
gcc -g -O2 -c ftp.c
gcc -static ftp.o common.o -o ftp
[root@rr2 test]#
This time make only rebuilt ftp because ftp.h is a dependency only for the target ftp.
However if you modify common.h, it will rebuild ftp, tftp and dnsresolver as follows:
[root@rr2 test]# make
gcc -g -O2 -c ftp.c
gcc -static ftp.o common.o -o ftp
gcc -g -O2 -c tftp.c
gcc -static tftp.o common.o -o tftp
gcc -g -O2 -c dnsresolver.c
gcc -static dnsresolver.o common.o -o dnsresolver
[root@rr2 test]#
Modifying common.c will cause rebuilding of all object files as well. This result of
make after modification in common.c is as follows:
[root@rr2 test]# make
gcc -g -O2 -c ftp.c
gcc -g -O2 -c common.c
gcc -static ftp.o common.o -o ftp
gcc -g -O2 -c tftp.c
gcc -static tftp.o common.o -o tftp
gcc -g -O2 -c dnsresolver.c
gcc -static dnsresolver.o common.o -o dnsresolver
[root@rr2 test]#
You can also use rules to build individual targets. For example, if you want to build only
ftp, you use the following command line instead:
[root@rr2 test]# make ftp
gcc -g -O2 -c ftp.c
gcc -g -O2 -c common.c
gcc -static ftp.o common.o -o ftp
[root@rr2 test]#