Problem Creating a Static Lib in Linux

Question

I am making a simple lib to use in my apps to save me the trouble of defining some functions over and over...

Here's my makefile:

CC=gcc
CFLAGS=-Wall -g -Wextra
OBJS=getline.o debug.o
LIB=libjimi.a
.PHONY: clean purge

libjimi.so : $(OBJS)
        ar rcs $(LIB) $(OBJS)
        @echo done!
%.o : %.c
        $(CC) $(CFLAGS) -c $^

clean :
        @rm *.o

purge : clean
        @rm $(LIB)

Now I get a segfault if I link the library, but if I link the object files that I link to create the library, it works...advice?

Do you mean youn get the seg fault at link time or when you run the linked executable? — anon
– anon, Commented Mar 13, 2009 at 0:11

Zitrax · Accepted Answer · 2009-03-13 00:15:05Z

2

Your target say libjimi.so which is the extension for a shared library, it should just be libjimi.a for a static lib.

And note that when you use a static lib you just link it in like any other object file, but with a shared lib you use the -l syntax.

answered Mar 13, 2009 at 0:15

Zitrax

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2 Comments

Jonathan Leffler Over a year ago

Of course you can link with -ljimi whether it is static or dynamic (for libjimi.a or libjimi.so). The library just needs to be in one of the directories searched (-L /some/where/lib to add directories; -L. is seldom necessary).

Zitrax Over a year ago

I think you are right but I remember my problem with that was that there exist both a libsomething.a and libsomething.so on my system and when I wanted the .a version the -l switch always picked the .so version instead of the .a version.

Jonathan Leffler · Accepted Answer · 2009-03-13 00:19:00Z

Static libraries on Linux (Unix) normally end with '.a'; shared objects end with '.so'. Your library rule is currently:

libjimi.so : $(OBJS)
    ar rcs $(LIB) $(OBJS)
    @echo done!

It should be:

$(LIB): $(OBJS)
    ar rcs $(LIB) $(OBJS)
    @echo done!

Personally, I tend to use

AR      = ar
ARFLAGS = rv

Leading to:

$(LIB): $(OBJS)
    $(AR) $(ARFLAGS) $(LIB) $(OBJS)

Now all aspects of the build can be tuned by setting macros - if necessary.

Without knowing where the crash is occurring, it is hard to know what might be causing it. One possibility is that because of the makefile confusion, you are linking with an old version of the library and not with the current working version.

Incidentally, it is not nice to conceal what a clean or purge target is doing; it is much better to let make echo the commands (no @ in front). The @ is entirely appropriate for the echo though; its absence would lead to the same information being presented twice.

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