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+The goal of the libc crate is to have CI running everywhere to have the
+strongest guarantees about the definitions that this library contains, and as a
+result the CI is pretty complicated and also pretty large! Hopefully this can
+serve as a guide through the sea of scripts in this directory and elsewhere in
+this project.
+
+# Files
+
+First up, let's talk about the files in this directory:
+
+* `run-travis.sh` - a shell script run by all Travis builders, this is
+  responsible for setting up the rest of the environment such as installing new
+  packages, downloading Rust target libraries, etc.
+
+* `run.sh` - the actual script which runs tests for a particular architecture.
+  Called from the `run-travis.sh` script this will run all tests for the target
+  specified.
+
+* `cargo-config` - Cargo configuration of linkers to use copied into place by
+  the `run-travis.sh` script before builds are run.
+
+* `dox.sh` - script called from `run-travis.sh` on only the linux 64-bit nightly
+  Travis bots to build documentation for this crate.
+
+* `landing-page-*.html` - used by `dox.sh` to generate a landing page for all
+  architectures' documentation.
+
+* `run-qemu.sh` - see discussion about QEMU below
+
+* `mips`, `rumprun` - instructions to build the docker image for each respective
+  CI target
+
+# CI Systems
+
+Currently this repository leverages a combination of Travis CI and AppVeyor for
+running tests. The triples tested are:
+
+* AppVeyor
+  * `{i686,x86_64}-pc-windows-{msvc,gnu}`
+* Travis
+  * `{i686,x86_64,mips,aarch64}-unknown-linux-gnu`
+  * `x86_64-unknown-linux-musl`
+  * `arm-unknown-linux-gnueabihf`
+  * `arm-linux-androideabi`
+  * `{i686,x86_64}-apple-{darwin,ios}`
+  * `x86_64-rumprun-netbsd`
+  * `x86_64-unknown-freebsd`
+  * `x86_64-unknown-openbsd`
+
+The Windows triples are all pretty standard, they just set up their environment
+then run tests, no need for downloading any extra target libs (we just download
+the right installer). The Intel Linux/OSX builds are similar in that we just
+download the right target libs and run tests. Note that the Intel Linux/OSX
+builds are run on stable/beta/nightly, but are the only ones that do so.
+
+The remaining architectures look like:
+
+* Android runs in a [docker image][android-docker] with an emulator, the NDK,
+  and the SDK already set up. The entire build happens within the docker image.
+* The MIPS, ARM, and AArch64 builds all use the QEMU userspace emulator to run
+  the generated binary to actually verify the tests pass.
+* The MUSL build just has to download a MUSL compiler and target libraries and
+  then otherwise runs tests normally.
+* iOS builds need an extra linker flag currently, but beyond that they're built
+  as standard as everything else.
+* The rumprun target builds an entire kernel from the test suite and then runs
+  it inside QEMU using the serial console to test whether it succeeded or
+  failed.
+* The BSD builds, currently OpenBSD and FreeBSD, use QEMU to boot up a system
+  and compile/run tests. More information on that below.
+
+[android-docker]: https://github.com/rust-lang/rust-buildbot/blob/master/slaves/android/Dockerfile
+
+## QEMU
+
+Lots of the architectures tested here use QEMU in the tests, so it's worth going
+over all the crazy capabilities QEMU has and the various flavors in which we use
+it!
+
+First up, QEMU has userspace emulation where it doesn't boot a full kernel, it
+just runs a binary from another architecture (using the `qemu-<arch>` wrappers).
+We provide it the runtime path for the dynamically loaded system libraries,
+however. This strategy is used for all Linux architectures that aren't intel.
+Note that one downside of this QEMU system is that threads are barely
+implemented, so we're careful to not spawn many threads.
+
+For the rumprun target the only output is a kernel image, so we just use that
+plus the `rumpbake` command to create a full kernel image which is then run from
+within QEMU.
+
+Finally, the fun part, the BSDs. Quite a few hoops are jumped through to get CI
+working for these platforms, but the gist of it looks like:
+
+* Cross compiling from Linux to any of the BSDs seems to be quite non-standard.
+  We may be able to get it working but it might be difficult at that point to
+  ensure that the libc definitions align with what you'd get on the BSD itself.
+  As a result, we try to do compiles within the BSD distro.
+* On Travis we can't run a VM-in-a-VM, so we resort to userspace emulation
+  (QEMU).
+* Unfortunately on Travis we also can't use KVM, so the emulation is super slow.
+
+With all that in mind, the way BSD is tested looks like:
+
+1. Download a pre-prepared image for the OS being tested.
+2. Generate the tests for the OS being tested. This involves running the `ctest`
+   library over libc to generate a Rust file and a C file which will then be
+   compiled into the final test.
+3. Generate a disk image which will later be mounted by the OS being tested.
+   This image is mostly just the libc directory, but some modifications are made
+   to compile the generated files from step 2.
+4. The kernel is booted in QEMU, and it is configured to detect the libc-test
+   image being available, run the test script, and then shut down afterwards.
+5. Look for whether the tests passed in the serial console output of the kernel.
+
+There's some pretty specific instructions for setting up each image (detailed
+below), but the main gist of this is that we must avoid a vanilla `cargo run`
+inside of the `libc-test` directory (which is what it's intended for) because
+that would compile `syntex_syntax`, a large library, with userspace emulation.
+This invariably times out on Travis, so we can't do that.
+
+Once all those hoops are jumped through, however, we can be happy that we're
+testing almost everything!
+
+Below are some details of how to set up the initial OS images which are
+downloaded. Each image must be enabled have input/output over the serial
+console, log in automatically at the serial console, detect if a second drive in
+QEMU is available, and if so mount it, run a script (it'll specifically be
+`run-qemu.sh` in this folder which is copied into the generated image talked
+about above), and then shut down.
+
+### QEMU setup - FreeBSD
+
+1. Download CD installer (most minimal is fine)
+2. `qemu-img create -f qcow2 foo.qcow2 2G`
+3. `qemu -cdrom foo.iso -drive if=virtio,file=foo.qcow2 -net nic,model=virtio -net user`
+4. run installer
+5. `echo 'console="comconsole"' >> /boot/loader.conf`
+6. `echo 'autoboot_delay="0"' >> /boot/loader.conf`
+7. look at /etc/ttys, see what getty argument is for ttyu0
+8. edit /etc/gettytab, look for ttyu0 argument, prepend `:al=root` to line
+   beneath
+
+(note that the current image has a `freebsd` user, but this isn't really
+necessary)
+
+Once that's done, arrange for this script to run at login:
+
+```
+#!/bin/sh
+
+sudo kldload ext2fs
+[ -e /dev/vtbd1 ] || exit 0
+sudo mount -t ext2fs /dev/vtbd1 /mnt
+sh /mnt/run.sh /mnt
+sudo poweroff
+```
+
+Helpful links
+
+* https://en.wikibooks.org/wiki/QEMU/Images
+* https://blog.nekoconeko.nl/blog/2015/06/04/creating-an-openstack-freebsd-image.html
+* https://www.freebsd.org/doc/handbook/serialconsole-setup.html
+
+
+### QEMU setup - OpenBSD
+
+1. Download CD installer
+2. `qemu-img create -f qcow2 foo.qcow2 2G`
+3. `qemu -cdrom foo.iso -drive if=virtio,file=foo.qcow2 -net nic,model=virtio -net user`
+4. run installer
+5. `echo 'set tty com0' >> /etc/boot.conf`
+6. `echo 'boot' >> /etc/boot.conf`
+7. Modify /etc/ttys, change the `tty00` at the end from 'unknown off' to
+   'vt220 on secure'
+8. Modify same line in /etc/ttys to have `"/root/foo.sh"` as the shell
+9. Add this script to `/root/foo.sh`
+
+```
+#!/bin/sh
+exec 1>/dev/tty00
+exec 2>&1
+
+if mount -t ext2fs /dev/sd1c /mnt; then
+  sh /mnt/run.sh /mnt
+  shutdown -ph now
+fi
+
+# limited shell...
+exec /bin/sh < /dev/tty00
+```
+
+10. `chmod +x /root/foo.sh`
+
+Helpful links:
+
+* https://en.wikibooks.org/wiki/QEMU/Images
+* http://www.openbsd.org/faq/faq7.html#SerCon
+
+# Questions?
+
+Hopefully that's at least somewhat of an introduction to everything going on
+here, and feel free to ping @alexcrichton with questions!
+