As I have used MinGW and Cygwin to compile GNU/Linux software in Windows, sometimes I only get static libraries, but not a shared library. After some research, I found several ways to convert a static library to a shared library. Using GCC with the -shared parameter is one way. libtool is another tool for such a task. In this post, I will write about dllwrap because that's what I have used and known to work.
Using dllwrap
Suppose the name of the static library is libpango-1.0.a This library is just an archive of many object files. Running “ar t libpango-1.0.a” will display the contents of the archive.
ar t libpango-1.0.a
Now, we have to extract the contents of the archive into an empty folder. Create a new folder.
mkdir temp
Change to the newly created folder and extract the static library.
cd temp
ar x libpango-1.0.a
Use dllwrap to create a shared library from the object files in the following manner:
dllwrap --verbose --export-all-symbols --add-stdcall-alias \
-o /usr/bin/cygpango-1.0-0.dll --dllname cygpango-1.0-0.dll \
--output-lib /usr/lib/libpango-1.0.dll.a *.o -L/usr/lib \
-lgobject-2.0 -lgmodule-2.0 -lglib-2.0 -luser32 -lkernel32 -lintl -liconv
This creates a shared library cygpango-1.0-0.dll and an import library libpango-1.0.dll.a. To learn more about dllwrap, read the output of “dllwrap --help”
Using GCC to convert a static library to shared library
You can also use GCC to do a library conversion with GCC. Here's an example. It's certainly a lot of typing:
ar x /usr/lib/libpango-1.0.a
gcc -shared -o libpango-1.0-0.dll -Wl,--out-implib=libpango-1.0.dll.a \
-Wl,--export-all-symbols -Wl,--add-stdcall-alias -Wl,--enable-auto-import -Wl,--enable-runtime-pseudo-reloc \
*.o -L/usr/lib \
-lgobject-2.0 -lgmodule-2.0 -lglib-2.0 -luser32 -lkernel32 -lintl -liconv
This creates the same set of files as with dllwrap above, but with slightly different sizes. For more information, read the GCC manual and the output from ld --help
Using a2dll to Convert a Static Library
a2dll is a little tool from mingw-utils that can be used to convert a static library to a dynamic library. For example,
a2dll libmp3lame.a -o lame_enc.dll
Is it possible to do this in the other direction too and create a static lib from the dll/so?
ReplyDeleteI think it's extremely difficult, if not impossible. My limited knowledge suggests that one may use objdump or dumpbin on a .so or .dll, then somehow reverse-engineer and extract object codes from the shared library and construct a static library from them as long as all symbols are still present. Sorry but I don't have a clear answer for your question.
ReplyDeleteI'm trying both with dllwrap and a2dll but I came across the same error:
ReplyDeletefoo.o: file not recognized: File format not recognized.
Any suggestion?
Sorry, but I haven't seen such an error when I used dllwrap or a2dll. My best approach is to simply use "gcc -shared".
Deletegcc -shared -o libfoo.dll -Wl,--out-implib,libfoo.dll.a -Wl,--whole-archive foo.a -Wl,--no-whole-archive -L/mingw/lib -lbar
where foo.a is the static library, libfoo.dll is the DLL you want to create and -lbar means you want to link it with /mingw/lib/libbar.a.
Thank you for your reply.
DeleteI try to explain you my situation a bit more in detail, so maybe you can help me, or at least give me an advice,since I'm screwed.
I am trying to compile the umfpack library, that is a solver for sparse matrices, under windows.
What I have is the static library under linux, that is libumfpack.a, and its dependances, that are libblas.a and libamd.a
I don't know so much about how this libraries were compiled and more in general I don't know anything about cross-compilation, MinGW ecc..
Can you please explain me if is possible to port directly this libraries under windows and - if so - what's the easiest way.
It has been 3 days that I am wandering around the whole web without succeding, and this stuff is driving me nuts.
If the library is written in pure ANSI C, you'll have little or no problem porting it to Windows with MinGW. But if it has Linux-specific codes, it could be compiled with Cygwin.
DeleteAfter installing MinGW or Cygwin, try running the following commands at the top-level folder.
cd Lib
make -f GNUmakefile
But before that, I think you should compile libamd, libblas, ufconfig first. Have you checked this site?