i have a c program that relies on a second library whose compilation i can control. i want to be able to compile my program into a shared object library without it linking to the second library. in other words i want a single monolithic shared object library at the end. how can i do this?
if i separately compile the second library into a .so and include that as a dependency when compiling my program, i can see that i need that file when i run ldd on the binary.
You need to compile your second library as a .a (static library) and statically link that into your c program.
Static linking is when object files are linked at compile time and are part of the final binary, the resulting executable can be executed with no dependencies..
Shared libraries (.so) are linked at run time and must be available when you execute the binary that links them.
the gcc flag to link statically is: -static this will automatically search for .a files.
What radman said above.
http://www.network-theory.co.uk/docs/gccintro/gccintro_25.html
Related
I need to include Security32.dll windows library into my project. Of course, I can load this library dynamically with LoadLibrary function, but is it possible to link the library during linking? I mean something like this (The following example is not correct, I just tried that and provide it as an example):
g++ -o bin main.o -lsecurity.dll
I really depends on your actual linker.
The GCC toolchain provided as part of the MinGW project will allow you to use dynamic link libraries (dll files) directly under Windows rather than static libraries only (or MSVC's lib files), but you'll still need the proper header files so the compiler knows what to call.
Microsoft Visual C++ on the other hand won't support this and will always need static libraries (lib files) with the proper information, even when you're linking against a dynamic/shared library.
I have built the boost 1.55 serialzation library with the following command:
b2 --build-dir=build toolset=gcc --with-serialization --layout=tagged link=static threading=multi stage
and got libboost_serialization-mt.a and libboost_wserialization-mt.a in my stage/lib directory - fine. Then I added boost_serialization to my C::B project's linker library list and compiled the boost serialization example and it ran fine from the command line. I then built the dynamic and single thread variants additionally using
b2 --build-dir=build toolset=gcc --with-serialization --layout=tagged link=static,shared threading=multi,single stage
and got more libraries in my stage/lib directory, as expected. What puzzles me is that there is a .so file for every library, even those that should be static. Why is it there? What is it needed for?
When I now compile the project, the executable complains:
error while loading shared libraries: libboost_serialization.so.1.55.0: cannot open shared object file: No such file or directory
The library is definitely there and I might just need to add the path to it to LD_LIBRARY_PATH, but I want to link statically for now. How can I do that?
I also don't quite understand the library naming: I have some libboost_wserialization... libraries in my lib folder and the w prefix to serialization is not described in the library naming section of the current boost getting started page.
Your answers gave me a better understanding of what was going on - now I know where the boost_wserialization libraries came from. I turned out that after doing the second build, all present libraries were shared, and the static libraries were overwritten. That's why I got confused by the "extra" .so files for those libraries which previously were indeed static.
Ok, first question:
Why is there a boost_serialization and boost_wserialization library?
the wserialization library is wchar_t oriented. Put into a separate library because it may not actually be needed.
Why are there multiple shared/static libraries?
The reason you're seeing all those extra shared libraries is because you're invoking b2 with link=static,shared, which instructs boost to build the shared libraries as well as the static libraries. Additionally, adding in the thread=multi causes the building of the mt libraries, which are libraries that should be used when linking to multi-threaded applications.
Why am I getting the run-time link error about libboost_serialization.so.1.55.0?
By default, most unix/linux systems will prefer the use of shared libraries over static libraries when linking, so when you try to link it will prefer to use the shared libraries over the static ones. If you want to force the link of the static library rather than the shared one, you tell the compile-time linker to do that, using:
-Wl,-Bstatic -lboost_serialization -Wl,-Bdynamic
This will cause the linker to look for the static variant of the boost_serialization library, rather than the dynamic one.
Now, because you're using code::blocks, I'd have to look up how to specify these flags on a case-by-case basis, but the most sensible thing to do is to clean the boost build using ./b2 clean and then rebuild, specifying only link=static, then you should end up with only .a files, which will produce stand-alone executables again.
If you want to specify this option for code::blocks, you would need to put them into the Build Settings -> Linker settings -> Other Linker Options field for the project. Simply specifying the library in the libraries field will not work for this case. Additionally, forgetting to pass in the -Wl,-Bdynamic option will cause it to try to link in static versions of some platform libraries, which can lead to build failure if the library in question is not present.
If you want to avoid having to set LD_LIBRARY_PATH to run the binary, you can add the option -Wl,-rpath,/path/to/boost/libraries, to the linker flags which will cause the compiled program to search that directory when trying to resolve the location of libraries.
What puzzles me is that there is a .so file for every library, even
those that should be static. Why is it there? What is it needed for?
You apparently are using someone else's make file. I wrote my own. My build command does not create a ".so" (shared object library). It only creates the ".a" (archive library). The linker knows how to use either.
See man ar. The utility ar builds archives.
See man ld. The utility ld can build shared objects.
You might look for these utility invocations in your build sequence, or ask someone where they are and comment out the use of ld, as you most likely do not need both (and building both will extend your build time unnecessarily). Alternatively, you might temporarily rename the ld command, and try your build. When it can not find the ld command, you might get a useful hint as to where the ld is invoked.
In my make file, the commands look like the following. The comment char is a # at beginning of line. (The string expansions $(AR) and $(LD) allow the use of non-standard utilities.)
$(TARGET_ARCHIVE): $(OBJ)
#echo R10: $(TARGET_ARCHIVE) :from: $(OBJ)
$(AR) crs $(TARGET_ARCHIVE) $(OBJ)
# $(TARGET_OLB) : $(OBJ)
# #echo R00: $(TARGET_OLB) :from: $(OBJ)
# $(LD) -o $(TARGET_OLB) -r $(OBJ)
The archive (.a), when used, is linked directly to and included in your executable. When the executable is loaded, all the referenced symbols of the .a are already in it. (un-referenced symbols and code are not linked in)
The shared object (.so) is not directly linked, but rather your executable gets a handle (or perhaps a file name) to the .so. It is my belief that when your executable is loaded, the .so is not immediately loaded. The .so does not load until the first time your executable references a symbol that is in the .so. At that loading, your app will experience a delay, but probably this late loading is reasonable for most applications.
It is also possible that the .so is already loaded in system memory before you activated your process. In that case, when your executable first references a symbol in the .so, some system code will 'map' the existing in-memory .so to your application -- probably faster than loading it, but I suppose the big benefit is that a .so that is used / referenced by many processes need only be loaded once, saving memory space. The loaded .so has all of its symbols, even if your app does not need all of them.
In either case, your executable will be smaller with .so's, bigger with .a's, but the .so's have some small performance hit for each .so that needs to be loaded or mapped in. With 4 GB in my desktop, the desktop has never felt 'crowded'. It's swap has never been used (afaik). So I generally use .a's.
NOTE: When the linker has access to both an archive (.a) and a shared object (.so) file, the linker will use the .so (and ignore the .a). Probably you can override that preference, but I have not tried. I find it easier to simply move the archive (.a) into a separate (from the .so's) directory, and inform the linker via the -L build option.
I've been using libarchive in my project for some time now and it's working great, at the moment I am dynamically linking to it, so on Windows the libarchive.dll file has to present on the system.
I would now like to statically link to the library so I don't have to bother distributing the DLL, but I'm having real trouble trying to achieve this!
Currently, in my make file, I have something like this:
-Lpath/to//libarchive/ -larchive
And this works, but it does a dynamic link. I don't know how to enforce a static link.
I can see in the libarchive directory there are two a files, libarchive.dll.a and libarchive_static.a. I suppose I want to link to libarchive_static.a but I can't seem to specify this, doing -larchive_static in the make file results in linker errors.
I was under the impression that static libraries under windows are lib files, but I get no such file type when I build libarchive.
How can I make a .lib file from libarchive. Also, as an extra question, what is the difference between an a file and a lib file?
Update
To statically link to libarchive, your library command for make should contain:
-Lpath/to//libarchive/ -larchive_static
This will link to the libarchive_static.a file. However, you also need to define LIBARCHIVE_STATIC in your code.
Now the problem is that libarchive depends on the bzip2 libraries (as well as others), and if you do not have a static build of them you will get linker errors something like:
undefined reference to `BZ2_bzCompressInit'
You need a static build of the dependent libraries and a similar command to the linker after the libarchive command:
-Lpath/to/bzip2/ -lbzip2
You can either build bzip2 from source, or do it the easy way and get a pre-built binary from the Gnu32Win project here: http://gnuwin32.sourceforge.net/packages.html
Just add libarchive_static.a explicitly to your link command.
gcc -o YourApp.exe $(OBJS) path/to/libarchive_static.a $(OtherLibs)
".lib" files differ from compiler to compiler (Borland, Microsoft etc.), ".a" is an old "archive" format from UNIX's ar tool. It is now used only for the bundling of static libraries.
Currently, in my make file, I have something ...
And this works, but it does a dynamic link
The .a file actually contains some code for dynamic linking to the .dll file, not the libarchive itself. On the startup the pointers to functions are allocated and dynamic linking is done.
I compile my my OpenCV programs as follows:
g++ `pkg-config --cflags opencv --libs opencv` <filename>.cpp
It works perfectly on my computer. Can I complile the shared libraries alone with the program so that it can be run on other computers which doesnt have opencv on it? If so, how do I do it?
The program during compilation are dynamically linked to Shared Libraries (.so files) on our computer. The executable compiled use these shared libraries during run-time. But these shared libraries may not be present on other computers, hence might not be able to run the executable.
Solution to this will be to statically link Archive Libraries (.a files) instead of dynamically linking Shared Libraries. OpenCV does not distribute archive libraries as such. So one will have to compile archive library from the its source using cmake -DBUILD_SHARED_LIBS=OFF. This archive library can be used to create standalone executable.
Yes to some degree: lookup static linking. Your opencv copy must have .a versions of the libraries (not just .so you mention) and that is also true for any other dependencies.
No. You need to use static libraries.
I want to build a shared library that uses ZipArchive using GNU Autotools but I'm having this problem:
Warning: linker path does not have real file for library -lziparch.
I have the capability to make that library automatically link in when
you link to this library. But I can only do this if you have a
shared version of the library, which you do not appear to have
because I did check the linker path looking for a file starting
with libziparch and none of the candidates passed a file format test
using a file magic. Last file checked: /usr/local/ZipArchive/ZipArchive/libziparch.a
The inter-library dependencies that have been dropped here will be
automatically added whenever a program is linked with this library
or is declared to -dlopen it.
If I build a static library or if I use a shared library of ZipArchive it works but the problem is that the makefile that comes with ZipArchive source code only builds a static library.
How can I force Libtool to link with a static library?
Generally, static archives are created with non-pic object files and they cannot be put into shared libraries.
What this message is telling you though, is that when a program links to YOUR library using Libtool, that -lziparch will get added to the link. So you don't need to change anything unless you're building a module for an interpreted language. In that case, you will have to build ZipArchive as a shared library. In addition, this wouldn't work on a platform like MS Windows where shared libraries (DLLs) have to resolve all their symbols at link time.
All that said, if your ziparch static lib is PIC code, you can use the -whole-archive flag when linking it to your library. This would be the least portable solution though.