OSX: How do I convert a static library to a dynamic one?

Question

Suppose I have a third party library called somelib.a on a Mac running Mountain Lion with Xcode 4.4 installed. I want to get a dynamic library out of it called somelib.dylib. An appropriate Linux command would be:

g++ -fpic -shared -Wl,-whole-archive somelib.a -Wl,-no-whole-archive -o somelib.so

where -whole-archive and -no-whole-archive are passed to the linker. When I do the equivalent for Mac:

g++ -fpic -shared -Wl,-whole-archive somelib.a -Wl,-no-whole-archive -o somelib.dylib

ld fails with an error:

ld: unknown option: -whole-archive

It seems that the ld on OSX is different from GNU ld. How do I have to modify above command so I will get the desired result?

Thank you in advance!

Answer 1

I found out the solution to my problem:

g++ -fpic -shared -Wl,-force_load somelib.a -o somelib.dylib

The required argument is -force_load:

• Which needs to be followed by a single library you wanna ensure gets loaded.
• I mean, it needs to be repeated for each library (unlike -noall_load approach, which wrapped them).
• For example, -Wl,-force_load libYetAnotherFile.a (where -Wl, part is only required because we don't pass parameter directly to linker).

Note that Old answer ^{(before edit)} was using -noall_load instead, but nowadays that causes a linker error (as -noall_load has been removed, was obsolete previously).

Answer 2

Note: A link for the documentation of the OSX ld linker.

http://www.unix.com/man-page/osx/1/ld/

I know it is late to give an answer for this, but I do not have enough reputation to make a comment on @hanslovsky answer. However, it helps me a lot to have the docs of the options too. It helps what the options do exactly, and that other options the ld linker also has. So I just wanted to share with others who finds linking an issue.

UPDATE:

After the comment from @GhostCat I have decided to expand my answer.

The docs for -all_load is:

-all_load

Loads all members of static archive libraries.

So it loads for all static libraries that you note. If you want something similar to --whole-archive and --no-whole-archive, then you need to use -force_load and -noall_load.

-force_load "path_to_archive"

Loads all members of the specified static archive library. Note: - all_load forces all members of all archives to be loaded.
This option allows you to target a specific archive.

-noall_load

This is the default. This option is obsolete.

Then you can define which libraries to fully load with -force_load and then later turn it off again with -noall_load.