FreeBSD support

[hannesm]

There are two changes needed to get PKCS11 (and the example application) to work on FreeBSD:

• include <dlfcn.h>
• don't use the RTLD_DEEPBIND flag on FreeBSD (since it is not defined there, and ctypes will raise an assertion failure otherwise).

The second item is done at runtime, after investigating the output of uname -s. Since Pkcs11.load_driver is called rarely, I guess spawning a new process which runs uname -s is ok.

[emillon]

Thanks for the patches. I think it's possible to remove the unconditional RTLD_DEEPBIND and make it an optional argument of load_driver, I'll have to check if that works with our use cases.

[hannesm]

I don't have a linux system to test, but the RTLD_DEEPBIND may actually not be needed at all...

[hannesm]

(NB, with this PR and https://github.com/Yubico/yubico-piv-tool/pull/113 being merged, I can successfully sign using a Yubikey NEO/.. using RSA-PSS. mission accomplished :) Thank you so much for this library and the example application!)

[emillon]

Re. deepbind: that was to work around a bug when using both forwards and reverse binding at the same time. I don't remember what the exact problem was so I'll check whether that works without this flag.

Glad that this library is helpful!

[emillon]

Those lwt test failures are a bit annoying. Restarting the build!

[emillon]

Thanks!

[hannesm]

thanks for merging -- btw your review comments (on the uname etc.) just appeared today -- maybe you forgot earlier to finish the review?

[emillon]

That's possible, that's the first time I'm using this feature so I didn't know it was necessary to submit. I'll know it for next time!

[hannesm]

any chance you can make a new release of pkcs11?

[emillon]

I have a couple patches I'd like to squeeze into this release, but that should be done by the end of the week.

[emillon]

Pull-requested! https://github.com/ocaml/opam-repository/pull/8976