I am building foo.so and that depends on bar.so. They will both be installed in the same location /some/lib, with the RUNPATH set appropriately to /some/lib. But they are built from different directories.
I'm trying to build them like:
cd /tmp/bar
gcc -o bar.o -c bar.c
ld -Bshareable -o bar.so bar.o
cd /tmp/foo
gcc -o foo.o -c foo.c
ld -Bshareable -rpath /some/libs -o foo.so foo.o ../bar/bar.so
ldd foo.so
But the problem is that ldd shows ../bar/bar.so. I can fix it by doing:
cd /tmp/bar
gcc -o bar.o -c bar.c
ld -Bshareable -o bar.so bar.o
cd /tmp/foo
gcc -o foo.o -c foo.c
cp ../bar/bar.so .
ld -Bshareable -rpath /some/lib -o foo.so foo.o bar.so
ldd foo.so
Now the ldd just show plain bar.so, which is right. But is there a better way that doesn't require copying or symlinking bar.so just for the link step?
Solution:
ld -Bshareable -rpath /some/lib -L../bar -o foo.so foo.o -l:bar.so
works without needing to copy bar.so to the current directory.
Related
I'm trying to compile a project that has multiple *.c files and *.h file when I type the following command:
$gcc -c -I ../hdr main.c gestic.c menu.c
the hdr folder is where the *.h files are located, the .o files are created but when I try to link them using the command:
$gcc -o main.o gestic.o menu.o
I see errors
gestic.c:(.text+0x..): undefined reference to functions that are declared in *.h files
$gcc -Wall -c -I../hdr -o main.o main.c
$gcc -Wall -c -I../hdr -o menu.o menu.c
$gcc -Wall -c -I../hdr -o gestic.o gestic.c
$gcc -Wall -o myprogram main.o menu.o gestic.o
Using a Makefile is very common for this task
example (untested) Makefile:
CC=gcc
CFLAGS=-Wall -I../hdr
all: myprogram
myprogram: main.o menu.o gestic.o
$(CC) -o $# $^
gestic.o: gestic.c
$(CC) $(CFLAGS) -c -o $# $<
main.o: main.c
$(CC) $(CFLAGS) -c -o $# $<
menu.o: menu.c
$(CC) $(CFLAGS) -c -o $# $<
Try:
$ gcc main.o gestic.o menu.o
-o filename: Place output in filename
Firstly header files are not included, secondly you might use the function that doesn't contain the definition.
The message undefined reference to 'function_name' implies that of all the object files you're giving to the linker, none of them has a definition for function_name. That means that either
You're not linking with *.o
*.c (as compiled) does not contain a definition for function_name -- by 'as compiled' I mean with all of the various preprocessor options you use on it.
here -Iinclude/
try,
gcc -c file.c -I<include_dir>
If you compile more files better to have makefile to create the objects of those files, link those objects along with header.
Sample makefile,
CC = gcc
CFLAGS = -Wall
INCLUDE = sample.h
OBJ = samople1.o sample2.o
%.o: %.c $(INCLUDE)
$(CC) $(CFLAGS) -c -o $# $<
go: $(OBJ)
gcc $(CFLAGS) -o $# $^
I was doing makefile test for creating static library and creating dynamic library from it. I have foo.h foo.c bar.c and main.c files in my directory.
I wrote a Makefile as follows:
#This makefile demonstrate the shared and static library creation.
CFLAGS = -Wall -Werror -fPIC
CFLAGS1 = -Wall
inc = /home/betatest/Public/implicit-rule-archive
all : foo.o bar.o libfoo.a libfoo.so run
foo.o: foo.c foo.h
#echo "Making the foo.o"
$(CC) -c $(CFLAGS) $< -o $#
bar.o : bar.c foo.h
#echo "Making the bar.o"
$(CC) -c $(CFLAGS) $< -o $#
libfoo.a(foo.o bar.o) : foo.o bar.o
ar cr $# $^
libfoo.so : libfoo.a
$(CC) -shared -o $# $^
run : main.c
$(CC) -L$(inc) $(CFLAGS1) -o $# $< -lfoo
.PHONY : clean
clean :
-rm -f *.o run libfoo.*
while making it gives the following the following errors:
Making the foo.o
cc -c -Wall -Werror -fPIC foo.c -o foo.o
Making the bar.o
cc -c -Wall -Werror -fPIC bar.c -o bar.o
make: *** No rule to make target 'libfoo.a', needed by 'all'. Stop.
I have written the archive statement as :
libfoo.a(foo.o bar.o) : foo.o bar.o
ar cr $# $^
from this to:
libfoo.a(*.o) : *.o
ar cr $# $^
Can I write the statement like this because in both the cases the error is the same.
I don't understand where I am going wrong. Thanks!!!!!
Instead of libfoo.a(foo.o bar.o) you want plain libfoo.a : foo.o bar.o.
Another thing is that .a files are normally built for linking against the final executable, hence object files for .a are compiled as position-dependent code. Shared libraries, on the other hand, require code compiled as position independent.
Hence, you can:
Get rid of libfoo.a.
Produce header dependencies automatically.
Establish complete dependencies on your targets so that make -j works robustly.
Set rpath so that run always finds libfoo.so in its directory.
This way:
CFLAGS = -Wall -Werror
LDFLAGS = -L/home/betatest/Public/implicit-rule-archive -Wl,-rpath,'$$ORIGIN'
all : run
run : main.o libfoo.so
$(CC) $(LDFLAGS) -o $# $^
libfoo.so : CFLAGS += -fPIC # Build objects for .so with -fPIC.
libfoo.so : foo.o bar.o
$(CC) -shared -o $# $^
# Compile any .o from .c. Also make dependencies automatically.
%.o : %.c
$(CC) -c $(CFLAGS) -o $# -MD -MP $<
# Include dependencies on subsequent builds.
-include $(wildcard *.d)
.PHONY : all clean
clean :
-rm -f *.o *.d run libfoo.*
Even though I have linked -lrt in my Makefile, as you can see below, I am still getting undefined reference to 'mq_open'. Please help!
all:get1 iserv1
get: get1.c
gcc -Wall -o get1 get1.c -lrt
iserv: iserv1.c
gcc -Wall -o iserv1 iserv1.c -lrt
clean:
rm -fr *~ get1 iserv1
Note -lrt should be at end not inbetween.
Your makefile is wrong
all:get1 iserv1
get: get1.c
gcc -Wall -o get1 get1.c -lrt
all has a prerequisite of get1 and iserv1. But you created a get target and an iserv target. So e.g. get1 will be compiled with the default make rules, which does not include -lrt (this should show if you look at the gcc commands that actually are executed.)
Your makefile should like like this:
all:get1 iserv1
get1: get1.c
gcc -Wall -o get1 get1.c -lrt
iserv1: iserv1.c
gcc -Wall -o iserv1 iserv1.c -lrt
clean:
rm -fr *~ get1 iserv1
I have used this command.
libtool --mode=compile gcc -g -o -c foo.c
Actual output should be like this after the command:
$libtool --mode=compile gcc -g -O -c foo.c
mkdir .libs
gcc -g -O -c foo.c -fPIC -DPIC -o .libs/foo.o
gcc -g -O -c foo.c -o foo.o >/dev/null 2>&1
but observed output is
$libtool --mode=compile gcc -g -O -c foo.c
gcc -g -O -c foo.c -fPIC -DPIC -o .libs/foo.o
gcc -g -O -c foo.c -o foo.o >/dev/null 2>&1.
.libs directory is not creating. It there any changes i have to make
http://www.gnu.org/software/libtool/manual/html_node/Creating-object-files.html
On shared library systems, libtool automatically generates an additional PIC object by inserting the appropriate PIC generation flags into the compilation command:
burger$ libtool --mode=compile gcc -g -O -c foo.c
mkdir .libs
gcc -g -O -c foo.c -fPIC -DPIC -o .libs/foo.o
gcc -g -O -c foo.c -o foo.o >/dev/null 2>&1
burger$
Note that Libtool automatically created .libs directory upon its first execution, where PIC library object files will be stored.
Since ‘burger’ supports shared libraries, and requires PIC objects to build them, Libtool has compiled a PIC object this time, and made a note of it in the libtool object:
# foo.lo - a libtool object file
# Generated by ltmain.sh (GNU libtool) 2.4.2
#
# Please DO NOT delete this file!
# It is necessary for linking the library.
# Name of the PIC object.
pic_object='.libs/foo.o'
# Name of the non-PIC object.
non_pic_object='foo.o'
Notice that the second run of GCC has its output discarded. This is done so that compiler warnings aren't annoyingly duplicated. If you need to see both sets of warnings (you might have conditional code inside ‘#ifdef PIC’ for example), you can turn off suppression with the -no-suppress option to libtool's compile mode:
burger$ libtool --mode=compile gcc -no-suppress -g -O -c hello.c
gcc -g -O -c hello.c -fPIC -DPIC -o .libs/hello.o
gcc -g -O -c hello.c -o hello.o
burger$
I hope this would be helpful.
Thanks & Regards,
Alok
I have a very small make file with content
VPATH = src
main: main.o
gcc -o main main.o
main.o: main.c
gcc -c main.c
Current directory contains a directory src which contains main.c
When I execute make, I get error
gcc -c main.c
gcc: main.c: No such file or directory
gcc: no input files
make: *** [main.o] Error 1
When I move main.c in the current directory, it works. It seems VPATH macro is not working. Please let me know the usage of VPATH.
While make locates main.c just fine, you are missing the use of the automatic variables here:
main.o : main.c
gcc -o $# -c $<
which will be expanded by make to the gcc call
gcc -o main.o -c src/main.c
Always use the automatic variables $< (first prerequisite) and $# (target) where you can, they make make both more powerful and easier to read.