The Design and Implementation of the Anykernel and Rump Kernels

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4.3.1 Non-native Hosting
When hosting NetBSD kernel code in a foreign environment, there are a number of
practical issues to consider:
1. Building the source code for the target system.
2. Accessing the host services from a rump kernel.
3. Interfacing with the rump kernel from clients.
For each subpoint, we offer further discussion based on experiences. We have had
success with non-native hosting of NetBSD rump kernels on Linux, FreeBSD and
various versions of NetBSD, including the NetBSD 4 and NetBSD 5 branches.
Building
First, we define the build host and the build target. The build host is the system the
build is happening on. The build target is the system that the build is happening
for, i.e. which system will be able to run the resulting binaries. For a kernel, the
target involves having a compiler targeted at the correct CPU architecture. For a
userspace program, it additionally requires having access to the target headers and
libraries for compiling and linking, respectively.
The build tool build.sh we already mentioned in Section 4.1.2 and Section 4.2.2
automatically builds the right tools and compiler so that the NetBSD source tree can
be built for a NetBSD target architecture on any given host. What we want is slightly
different: a compilation targeted for a non-NetBSD system. Having build.sh provide