LWIP Makefile error

Question

After going through the LWIP documents, I wrote a simple tcp echo server code. To compile it and create an executable I wrote the following Makefile. Now, when I run the command make all, it gives error for each of .c files included in the makefile.
The file structure is as follows: 1. tcp_server.c is the main file where I create the tcp server. 2. It uses the tcp_new(), tcp_bind() etc functions defined in "lwip-1.4.1/src/core/lwip/tcp.c" and "lwip-1.4.1/src/core/lwip/tcp_out.c" and I have given the paths for compilation accordingly.

I am just a beginner in writing makefiles and have written the following file going through the GNU Make documentation.

CC=gcc

CFLAGS= -g -Wall

LWIPDIR=../lwip-1.4.1/src

TARGET=tcp_server

INCLUDES= -I../lwip-1.4.1/src/include -I../STABLE-1_4_0/ports/unix/proj/lib\
        -I../STABLE-1_4_0/ports/unix/include -I../lwip-1.4.1/src/include/ipv4

LFLAGS= -L../STABLE-1_4_0/ports/unix/proj/lib/liblwip.so

#LIBS= -llwip

COREFILES=$(LWIPDIR)/core/tcp.c $(LWIPDIR)/core/tcp_out.c

VPATH = $(LWIPDIR)/core

OBJS = tcp_server.o tcp.o tcp_out.o

MAIN=tcp_server

all : edit

edit : $(OBJS)
        $(CC) $(CFLAGS) $(INCLUDES) -o edit $(OBJS) $(LFLAGS)

tcp_server.o : tcp_server.c tcp.o tcp_out.o
        $(CC) $(CFLAGS) $(INCLUDES) -c tcp_server.c $(LFLAGS)

tcp.o : $(LWIPDIR)/core/tcp.c
        $(CC) $(CFLAGS) $(INCLUDES) -c $(LWIPDIR)/core/tcp.c $(LFLAGS)

tcp_out.o : $(LWIPDIR)/core/tcp_out.c
        $(CC) $(CFLAGS) $(INCLUDES) -c $(LWIPDIR)/core/tcp_out.c  $(LFLAGS)

clean :
        rm -f *.o

All the files include certain headers defined in "lwip-1.4.1/src/include" and I given the arguments to -I accordingly. However on running make, the output shows "Undefined reference to" all the functions which are defined in the lwip header files. What could be the reason? Where I am going wrong?

Thank you for all the help.

Try using the absolute address of the include files rather than the relative address of the include files for ${INCLUDES} — sabbahillel
@sabbahillel have done that, but to no avail. Isn't there any visible error in the syntax or logic of the Makefile? — codeahead

cleblanc cleblanc · Accepted Answer · 2016-01-11T15:14:27

UNDEFINED REFERENCE is a linker error so you should;

For gcc you should use -L to specify the directory your libraries are contained and use -l to link a particular library. For example change the line in your makefile;

LFLAGS= -L../STABLE-1_4_0/ports/unix/proj/lib

remove the comment before LIBS and change this target

edit : $(OBJS)
        $(CC) $(CFLAGS) $(INCLUDES) -o edit $(OBJS) $(LFLAGS) $(LIBS)

LWIP Makefile error

1 Answers