I have a Makefile for linux that I am porting over to Darwin. The makefile takes a bunch of .o files and links them together into a .so shared object. Okay, so I figured (am I wrong about this?) that the best analog for this in Darwin is the dylib. So I changed the -shared flag to -dynamiclib.
Now the code that I am linking together into the dylib depends on lots of external libraries. When I try to build the dylib, I get errors saying there are undefined references. But the Linux Makefile does not specify any of the -lwhatever or -L/path/whatever options in the build step that creates the .so file. Hm? Is this because when you create an ELF .so file, by default it leaves external references unresolved, and then when the shared library is loaded, it recursively loads shared libraries which are depended on by the shared library you are loading? Wouldn't it be the case that if the shared library depends on a .a or .o file, you would HAVE to statically link them into the shared library, otherwise you could not link at runtime? How can you get away with having undefined references in a library that is loaded at runtime, unless the references are also to dynamically loadable libraries?
Anyway so if I specify
-undefined suppress -flat_namespace
it doesn't require me to add those -l and -L options when creating the shared library. But I still don't understand how this can work ultimately.
This thread also discusses this issue. I think the key point is that in order to get the Linux-like linking behavior, you need to specify the "-undefined dynamic_lookup" flag. By default, the Darwin linker throws an error if there are any undefined references in a dynamic library. You can also use -U to set this behavior on a per-symbol basis. See 'man ld' for reference.
Use libtool.
libtool -dynamic -multiply_defined suppress -install_name `basename ../../../../rlp/lib/universal-darwin9-gcc40/libbtutils.dylib` -o ../../../../rlp/lib/universal-darwin9-gcc40/libbtutils.dylib ../../../../rlp/lib/universal-darwin9-gcc40/libbtd.a ../../../../rlp/lib/universal-darwin9-gcc40/libbttrie.a ../../../../rlp/lib/universal-darwin9-gcc40/libbtkey.a ../../../../rlp/lib/universal-darwin9-gcc40/libbtunit.a ../../../../rlp/lib/universal-darwin9-gcc40/libbtutilities.a ../../../../rlp/lib/universal-darwin9-gcc40/libbtopts.a ../../../../rlp/lib/universal-darwin9-gcc40/libbtxcode.a ../../../../rlp/lib/universal-darwin9-gcc40/libbtprops.a ../../../../rlp/lib/universal-darwin9-gcc40/libbtxml.a ../../../../rlp/lib/universal-darwin9-gcc40/libbttake3.a ../../../../rlp/lib/universal-darwin9-gcc40/libbttake5.a ../../../../rlp/lib/universal-darwin9-gcc40/libbtac.a -lstdc++.6 -lgcc_s.10.4 ../../../../build_system/lib/universal-darwin9-gcc40/libgcc.a -lSystem -lSystemStubs`
Related
I make a program using a dynamic library, libexample.so. The dynamic library depends on another dynamic library, libtool.so.
It looks linker succeeded linking the libexample.so because of message from gcc.
Building target: libexample.so
Invoking: GCC C++ Linker
g++ -L/home/takehiro/Documents/documents/code/lib/tool -shared -o "libexample.so" ./classes/example.o ./classes/example_template.o ./classes/example_test.o ./classes/impl.o -ltool
Finished building target: libexample.so
cp libexample.so /home/takehiro/Documents/documents/code/lib/example
However, it failed to link it with the libtool.so.
ldd /home/takehiro/Documents/documents/code/lib/example/libexample.so
...
libtool.so => not found
...
I checked existence of the libtool.so under /home/takehiro/Documents/documents/code/lib/tool which is pointed by -L optoin at above linker by
ls /home/takehiro/Documents/documents/code/lib/tool
libtool.so
This is the first time to use a dynamic library depending another dynamic library. So I am so confused. Is it normal or malfunction? Why it cannot link them?
Does someone have a suggestion or a solution to me? I am very glad it.
Thank you very much.
All that the -L option does is tell the linker where the shared library is, at link time.
This does not have any effect on where the runtime loader searches for shared libraries. That's why the shared library fails to be loaded at runtime.
You also need to pass the -rpath option to the linker, when you're linking your shared library, in order to set the RPATH attribute on the shared library, that specifies where its dependencies are to be searched for. Something like
g++ -L/home/takehiro/Documents/documents/code/lib/tool \
-Wl,-rpath=/home/takehiro/Documents/documents/code/lib/tool \
... remaining options
I am trying to cross-compile apache-qpid for an arm system from a debian.
There is undefined reference to __dlopen error, but it seems that it is related to the previous warning:
using 'dlopen' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking ...
Here is the detail:
[ 86%] Linking CXX shared library libqpidcommon.so
CMakeFiles/qpidcommon.dir/qpid/sys/posix/Shlib.cpp.o: In function
`qpid::sys::Shlib::load(char const*)':
/home/mert/qpid-cpp-0.34/src/qpid/sys/posix/Shlib.cpp:32: warning: Using
'dlopen' in statically linked applications requires at runtime the shared
libraries from the glibc version used for linking
/home/mert/IDE/cVEND/00.00.14/bin/../arm-feig-linux-
gnueabi/sysroot/usr/lib/libdl.a(dlopen.o): In function `dlopen':
dlopen.c:(.text+0xc): undefined reference to `__dlopen'
I do not know what is happening exactly and how to solve it.
Here there is a similiar thing, I tried to add -static -ldl -lc C_FLAGS but made no difference.
Any help appreciated.
EDIT :
EDIT :
I am not sure exactly what is solved the problem, but I think that -ldl was looking exactly for libdl.so, but in arm directory, it was libdl-2.19.so, thus, probably it was then looking for and finding in another directory. I have linked libdl.so to libdl-2.19.so and now it is compiling.
The linker needs the options, not the compiler. See LDFLAGS.
https://www.gnu.org/software/make/manual/html_node/Implicit-Variables.html
Extra flags to give to compilers when they are supposed to invoke the
linker, ‘ld’, such as -L. Libraries (-lfoo) should be added to the
LDLIBS variable instead.
If this error occurs during the make step try doing
make LIBS=-ldl
And make sure the library path is present in LDFLAGS
export LDFLAGS=-L<path/to/ldl>
I want to start with a simple linking usage to explain my problem. Lets assume that there is a library z which could be compiled to shared library libz.dll(D:/libs/z/shared/libz.dll) or to static library libz.a (D:/libs/z/static/libz.a).
Let I want to link against it, then I do this:
gcc -o main.exe main.o -LD:/libs/z/static -lz
According to this documentation, gcc would search for libz.a, which is
archive files whose members are object files
I also can do the following:
gcc -o main.exe main.o -LD:/libs/z/shared -lz
It is not mentioned in the documentation above that -l flag will search for lib<name>.so.
What will happen if I libz.a and libz.dll will be in the same directory? How the library will be linked with a program? Why I need the flags -Wl,-Bstatic and -Wl,-Bdynamic if -l searches both for shared and static libraries?
Why some developers provide .a files with .dll files for the same modules, if I compile a shared library distribution?
For example, Qt provides .dll files in bin directory with .a files in lib directory. Is it the same library, but built like shared and static, respectively? Or .a files are some kind of dummy libraries which provide linking with shared libraries, where there are real library implementations?
Another example is OpenGL library on Windows. Why every compiler must provide the static OpenGL lib like libopengl32.a in MingW?
What are files with .dll.a and .la extensions used for?
P.S. There are a lot of questions here, but I think each one depends on the previous one and there is no need to split them into several questions.
Please, have a look at ld and WIN32 (cygwin/mingw). Especially, the direct linking to a dll section for more information on the behavior of -l flag on Windows ports of LD. Extract:
For instance, when ld is called with the argument -lxxx it will attempt to find, in the first directory of its search path,
libxxx.dll.a
xxx.dll.a
libxxx.a
cygxxx.dll (*)
libxxx.dll
xxx.dll
before moving on to the next directory in the search path.
(*) Actually, this is not cygxxx.dll but in fact is <prefix>xxx.dll, where <prefix> is set by the ld option -dll-search-prefix=<prefix>. In the case of cygwin, the standard gcc spec file includes -dll-search-prefix=cyg, so in effect we actually search for cygxxx.dll.
NOTE: If you have ever built Boost with MinGW, you probably recall that the naming of Boost libraries exactly obeys the pattern described in the link above.
In the past there were issues in MinGW with direct linking to *.dll, so it was advised to create a static library lib*.a with exported symbols from *.dll and link against it instead. The link to this MinGW wiki page is now dead, so I assume that it should be fine to link directly against *.dll now. Furthermore, I did it myself several times with the latest MinGW-w64 distribution, and had no issues, yet.
You need link flags -Wl,-Bstatic and -Wl,-Bdynamic because sometimes you want to force static linking, for example, when the dynamic library with the same name is also present in a search path:
gcc object1.o object2.o -lMyLib2 -Wl,-Bstatic -lMyLib1 -Wl,-Bdynamic -o output
The above snippet guarantees that the default linking priority of -l flag is overridden for MyLib1, i.e. even if MyLib1.dll is present in the search path, LD will choose libMyLib1.a to link against. Notice that for MyLib2 LD will again prefer the dynamic version.
NOTE: If MyLib2 depends on MyLib1, then MyLib1 is dynamically linked too, regardless of -Wl,-Bstatic (i.e. it is ignored in this case). To prevent this you would have to link MyLib2 statically too.
I have a problem, i want to compile my application with static linking of mysql connector.
My command line:
g++ -o newserver stdafx.cpp ... -lboost_system -lboost_thread
-lpthread -lmysqlcppconn -static /usr/lib/libmysqlcppconn-static.a -std=c++0x
But i have error:
/usr/bin/ld: cannot find -lmysqlcppconn
/tmp/ccxpOfdZ.o: In function `IsEqualsDns(unsigned long, std::basic_string<char, std::char_traits<char>, std::allocator<char> >)':
Server.cpp:(.text+0x356e): warning: Using 'gethostbyname' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
collect2: ld returned 1 exit status
How can i fix this?
Thanks!
Where is the library libsqlcppconn.a or libsqucppconn.so
(static or dynamic)? The compiler is looking for it, and
doesn't find it.
Presumably, this is the same library as
/usr/lib/mysqlcppconn-static.a. If so, just drop the
-lmysqlcppconn. Or just use -lmysqlcppconn-static (no
spaces), and forget about the /usr/lib/libmysqlconn-static.a.
With a name like that, there shouldn't be a corresponding .so,
which means that g++ will link it statically, even without the
-static. You only need the -static if there is both
a libmysqlconn-static.so and a libmysqlconn-static.a in the
same directory.
With regards to the second error (which is just a warning, but
will cause problems if you try to run the linked program on
other machines, or even after an upgrade of your machine): if
you use -static anywhere in your command line (as you
currently do), then it applies to all files linked afterwards.
Including the system libraries, which you don't want to link
statically. My guess is that the -static isn't necessary (see
above); if it is, place it immediately before the library you
want to link statically, and place a -dynamic immediately
after (so that any following libraries, including the system
libraries, will be dynamically linked).
You could try g++ -static YOUR ARGUMENTS.
If you are coming from a Windows platform, linking against Boost can give a few surprises. The typicall Boost installation (e.g. after ./b2 install) will make both dynamic and static libraries and put them in the same directory. Typically, the two library forms only differ in their extension (.so or .a).
Windows supports auto-linking, which basically means that library files contain some flags in their first few bytes indicating whether they are for dynamic or for static linking. On Linux platforms, this is not the case and the linker gets confused which file to load (since you don't provide the extension of the library name). Therefore, you need to tell your linker which form of linking you want.
I have a linux based OS with a lot of system libraries compiled as static libraries.
How can I use such libraries in my application, and link them to my final binary?
You use them as you do use shared libraries, except that you link against statically. An introduction to GCC - shared libraries and static libraries article will get you started.
I've trouble to understand. If you are linking with something like
g++ -o myprog myprog.o obj1.o obj2.o -L/path/to/lib -L/path2/to/lib -llib1 -llib2 -lib3
the linker called through the gcc or g++ wrapper will do "the right thing(tm)", if liblib1.so exist in the library path (/path/to/lib, /path2/to/lib plus a set of system specific directories where system libraries probably are), it will be linked dynamically, if not liblib1.a will be linked statically. The only thing to be aware of, is that if there are mutual dependencies in static libaries (lib1 needs lib2 and lib2 needs lib1), you may need to repeat them several times or use the --start-group and --end-group options of ld to mark libraries which needs to be considered together.