I just found out that the GNU Hurd does not provide the 'SA_SIGINFO' constant, although it supplies the 'sigaction' function. There is nothing in the manual of sigaction ($ man sigaction) to indicate this. In fact the manual explains the usage of 'sigaction' with 'SA_SIGINFO'.

Apparently 'SA_SIGINFO' is a POSIX XSI extension and one should check its availability at compile time.

Thanks to the #hurd folks, especially Richard Braun (nick: syn) and Guillem Jover (nick: braindmg) for their help.

If you are keen to have access to a GNU system running the GNU Hurd kernel instead of the Linux kernel, and do not have a machine to spare in order to install it, then you can request for a shell account here.

I now have a couple of shell accounts on two different GNU systems. Hopefully I will be able to learn something about the Hurd kernel in particular and microkernel based operating systems in general.