Hi there.

3.5.1 final didn't have this problem, 3.5.2 final does have this problem.

I'm compiling Python 3.5.2 under Debian, and get this warning during the ./configure step:

---------------
configure: WARNING: linux/random.h: present but cannot be compiled
configure: WARNING: linux/random.h:     check for missing prerequisite headers?
configure: WARNING: linux/random.h: see the Autoconf documentation
configure: WARNING: linux/random.h:     section "Present But Cannot Be Compiled"
configure: WARNING: linux/random.h: proceeding with the compiler's result
configure: WARNING:     ## -------------------------------------- ##
configure: WARNING:     ## Report this to http://bugs.python.org/ ##
configure: WARNING:     ## -------------------------------------- ##
---------------

Please check this?

Forgot to mention - this is for Debian 4. A really old legacy system we're running, but where we like to use new versions of Python.

FWIW adding a blank fourth argument in configure.ac silences this warning (and speeds up the configure run by 7%, or 4 s). But I don’t want to become an Autoconf nerd and I don’t know if this change could have negative consequences on other platforms (e.g. perhaps AC_INCLUDES_DEFAULT matters?).

Practically, I think you can ignore the warning. The include file is needed to use a new getrandom() syscall on Linux (see Issue 26839), but Python should fall back to older code if it cannot use getrandom().

Presumably this also affects Python 3.6, as that includes the same headers during configure for the same reasons: to check if the getrandom() syscall is likely to be available.

#27990 is somewhat related, in that Linux makes this a bit difficult to do correctly on older systems - we may need an explicit "--with-getrandom" and corresponding "--without-getrandom" to make it easy for folks to override the system inspection logic in the configure script.