CODEWITHSUNDEEP
makefileshared-libraries
Edward Diener
Edward Diener

Reputation: 97

Makefile dependency when creating shared library links

In a project I have an already created shared library called, let's say, 'myshare'. The library is already created as 'libmyshare.so.1.0.0' and its location is relative to the makefile at a relative address of 'adir/lib'.

In the makefile I want to create symbolic links for the shared library with the names 'libmyshare.so.1' and 'libmyshare.so'. In order to do this in the makefile I have these lines:

MYSHAREL = ./adir/lib/libmyshare.so.1.0.0
MYSHAREL1 = ./adir/lib/libmyshare.so.1
MYSHAREL2 = ./adir/lib/libmyshare.so
MYSHARELIBS = $(MYSHAREL) $(MYSHAREL1) $(MYSHAREL2)

.PHONY: all
all: myexetarget

myexetarget : various_files $(MYSHARELIBS)
    various_commands_to_make_target

$(MYSHAREL1): $(MYSHAREL)
    @echo "Creating symbolic link $(MYSHAREL1)"
    @ln -s $(MYSHAREL) $(MYSHAREL1)

$(MYSHAREL2): $(MYSHAREL)
    @echo "Creating symbolic link $(MYSHAREL2)"
    @ln -s $(MYSHAREL) $(MYSHAREL2)

When I run the 'make' command the links to the shared library are always created even when they already exist and even when the date of the shared library is prior to the date of already created symbolic links. Furthermore when I try to actually link to the shared library in my target, despite an -L./adir/lib and -lmyshare options among the linker options ( not shown above ) the link fails with:

/usr/bin/ld: cannot find -lmyshare

Both these problems lead me to believe that I am not specifying the name or relative location of the shared library correctly for the makefile processing to understand it. Does anybody know what I am doing wrong ?

Upvotes: 0

Views: 799

Answers (1)

Renaud Pacalet
Renaud Pacalet

Reputation: 29040

Your use of ln -s is probably the cause of your problem. If, from your top directory you execute:

ln -s ./adir/lib/libmyshare.so.1.0.0 ./adir/lib/libmyshare.so.1

(which is what your make rule does) a symbolic link is created in ./adir/lib, named libmyshare.so.1 and pointing to ./adir/lib/libmyshare.so.1.0.0:

$ cd ./adir/lib
$ ls -l
libmyshare.so.1 -> ./adir/lib/libmyshare.so.1.0.0
libmyshare.so.1.0.0

So, ./adir/lib/libmyshare.so.1 actually points to ./adir/lib/adir/lib/libmyshare.so.1.0.0 that does not exist.

You can replace your ln -s command by:

@ln -sr $(MYSHAREL) $(MYSHAREL1)

Same for MYSHAREL2. The -r option of ln create symbolic links relative to link location.

Upvotes: 1

Related Questions