Creating a simple Makefile to build a shared library

Question

I am trying to create a very basic hand crafted Makefile to create a shared library to illustrate a point.

This is what I have so far:

SHELL = /bin/sh CC    = gcc FLAGS        = -std=gnu99 -Iinclude CFLAGS       = -fPIC -pedantic -Wall -Wextra -march=native -ggdb3 DEBUGFLAGS   = -O0 -D _DEBUG RELEASEFLAGS = -O2 -D NDEBUG -combine -fwhole-program  TARGET  = example.so SOURCES = $(shell echo src/*.c) HEADERS = $(shell echo include/*.h) OBJECTS = $(SOURCES:.c=.o)  PREFIX = $(DESTDIR)/usr/local BINDIR = $(PREFIX)/bin  all: $(TARGET)  $(TARGET): $(OBJECTS)     $(CC) $(FLAGS) $(CFLAGS) $(DEBUGFLAGS) -o $(TARGET) $(OBJECTS) 

When I run make, it attempts to build an application - and ld fails because it can't resolve main().

Problem seems to be with CFLAGS - I have specified -fPIC but that is not working - what am I doing wrong?

Edit

I added the -shared flag as suggested, when I run make, I got this error:

gcc -std=gnu99 -Iinclude -fPIC -shared -pedantic -Wall -Wextra -march=native -ggdb3 -O0 -D _DEBUG -o example.so src/example.o /usr/bin/ld: src/example.o: relocation R_X86_64_32 against `.rodata' can not be used when making a shared object; recompile with -fPIC src/example.o: could not read symbols: Bad value collect2: ld returned 1 exit status make: *** [example.so] Error 1 

Which seems to be suggesting to revert back to -fPIC only.

BTW, my new CFLAGS setting is:

CFLAGS       = -fPIC -shared -pedantic -Wall -Wextra -march=native -ggdb3 

I am running gcc v4.4.3 on Ubuntu 10.0.4.

Answer 1

The solution was to modify the XXFLAGS as follows:

FLAGS        = # -std=gnu99 -Iinclude CFLAGS       = -fPIC -g #-pedantic -Wall -Wextra -ggdb3 LDFLAGS      = -shared 

Answer 2

Compile with -shared:

gcc -o libfoo.so module1.o module2.o -shared 

(This also works on MingW under Windows to produce DLLs.)