Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Implement vdso - virtual dynamic shared object. Through vdso Linux
exposes functions from kernel with proper DWARF CFI information so that
it becomes easier to unwind through them.
Using vdso is a mandatory for a thread cancelation && cleanup
on a modern glibc.

Differential Revision: https://reviews.freebsd.org/D1060

To reduce code duplication introduce linux_copyout_rusage() method.
Use it in linux_wait4() system call and move linux_wait4() to the MI path.
While here add a prototype for the static bsd_to_linux_rusage().

Differential Revision: https://reviews.freebsd.org/D2138
Reviewed by: trasz

Remove dead code.

MFC after: 1 Week

Segment registers are stored in the uc_mcontext member of the struct
l_ucontext. To restore the registers content, trampoline needs to
dereference uc_mcontext instead of taking some undefined values from
l_ucontext.

Submitted by: Dmitry Chagin <dchagin@>
MFC after: 1 week

Add preliminary support for running 32-bit Linux binaries on amd64, enabled
with the COMPAT_LINUX32 option. This is largely based on the i386 MD Linux
emulations bits, but also builds on the 32-bit FreeBSD and generic IA-32
binary emulation work.

Some of this is still a little rough around the edges, and will need to be
revisited before 32-bit and 64-bit Linux emulation support can coexist in
the same kernel.