libc/ci/README.md

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.

Note that this documentation is quite outdated. See CI config and scripts
in the `ci` directory how we run CI now.

# Files

First up, let's talk about the files in this directory:

* `run-docker.sh` - a shell script run by most builders, it will execute
  `run.sh` inside a Docker container configured for the target.

* `run.sh` - the actual script which runs tests for a particular architecture.

* `dox.sh` - build the documentation of the crate and publish it to gh-pages.

# CI Systems

Currently this repository leverages a combination of GitHub Actions and Cirrus CI
for running tests. You can find tested triples in [Actions config] or [Cirrus config].

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 BSD builds, currently OpenBSD and FreeBSD, use QEMU to boot up a system
  and compile/run tests. More information on that below.

[Actions config]: https://github.com/rust-lang/libc/tree/master/.github/workflows
[Cirrus config]: https://github.com/rust-lang/libc/blob/master/.cirrus.yml
[android-docker]: https://github.com/rust-lang/libc/blob/master/ci/docker/x86_64-linux-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.

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.
* We resort to userspace emulation (QEMU).

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 CI, 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 the latest stable amd64-bootonly release ISO](https://www.freebsd.org/where.html).
   E.g. FreeBSD-11.1-RELEASE-amd64-bootonly.iso
2. Create the disk image: `qemu-img create -f qcow2 FreeBSD-11.1-RELEASE-amd64.qcow2 2G`
3. Boot the machine: `qemu-system-x86_64 -cdrom FreeBSD-11.1-RELEASE-amd64-bootonly.iso -drive if=virtio,file=FreeBSD-11.1-RELEASE-amd64.qcow2 -net nic,model=virtio -net user`
4. Run the installer, and install FreeBSD:
   1. Install
   1. Continue with default keymap
   1. Set Hostname: freebsd-ci
   1. Distribution Select:
      1. Uncheck lib32
      1. Uncheck ports
   1. Network Configuration: vtnet0
   1. Configure IPv4? Yes
   1. DHCP? Yes
   1. Configure IPv6? No
   1. Resolver Configuration: Ok
   1. Mirror Selection: Main Site
   1. Partitioning: Auto (UFS)
   1. Partition: Entire Disk
   1. Partition Scheme: MBR
   1. App Partition: Ok
   1. Partition Editor: Finish
   1. Confirmation: Commit
   1. Wait for sets to install
   1. Set the root password to nothing (press enter twice)
   1. Set time zone to UTC
   1. Set Date: Skip
   1. Set Time: Skip
   1. System Configuration:
      1. Disable sshd
      1. Disable dumpdev
   1. System Hardening
      1. Disable Sendmail service
   1. Add User Accounts: No
   1. Final Configuration: Exit
   1. Manual Configuration: Yes
   1. `echo 'console="comconsole"' >> /boot/loader.conf`
   1. `echo 'autoboot_delay="0"' >> /boot/loader.conf`
   1. `echo 'ext2fs_load="YES"' >> /boot/loader.conf`
   1. Look at `/etc/ttys`, see what getty argument is for `ttyu0` (E.g. `3wire`)
   1. Edit `/etc/gettytab` (with `vi` for example), look for `ttyu0` argument,
      prepend `:al=root` to the line beneath to have the machine auto-login as
      root. E.g.

          3wire:\
                   :np:nc:sp#0:
      becomes:

          3wire:\
                   :al=root:np:nc:sp#0:

   1. Edit `/root/.login` and put this in it:

          [ -e /dev/vtbd1 ] || exit 0
          mount -t ext2fs /dev/vtbd1 /mnt
          sh /mnt/run.sh /mnt
          poweroff

   1. Exit the post install shell: `exit`
   1. Back in in the installer choose Reboot
   1. If all went well the machine should reboot and show a login prompt.
      If you switch to the serial console by choosing View > serial0 in
      the qemu menu, you should be logged in as root.
   1. Shutdown the machine: `shutdown -p now`

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!