# `arm64` build notes

Google _really_ wants anything arm-related to be cross-compiled
instead of built on the ARM device. A pity, because @groundwater
found a [really awesome and cheap](https://packet.net) service
that rents out 96-core `arm64` servers.

The current Electron build infrastructure is designed to make it
quick for end-user developers to put together their apps. Many
pieces that are built at the same time are packaged separately,
because some or all of them may be unnecessary most of the time.
This makes bootstrapping new architectures a little tricky,
because it's difficult to make compatible one-off builds of those
tools. For example, `mksnapshot` is necessary to build the
snapshot that is, by default, _required_ for the core Atom UI
modules to be loaded into the editor, and because it generates
partially-compiled code meant to be consumed directly by a
specific version of V8, is difficult to build without knowing the
settings after the fact.

We used `gn` to build `arm64`-native and cross-targeted `linux-x64` builds
of `mksnapshot` (that could be built using `ninja` instead of dealing with
`gyp`). Neither produced a blob for V8 that worked, even though I'm pretty
sure we had matching versions of V8. Using a `mksnapshot` built from the same
tree as the rest of `libchromiumcontent` and `v8` would probably solve this
problem.

## from the Google tree

1. `electron` is built locally instead of pulled from the GH releases page,
   and requires patches to be made to the installed copies of
   `electron-packager` and `electron-download`.
1. `dump_syms`, which is used by `minidump`, and is a part of `breakpad`,
   depends on a set of macros that need to have support for whatever ARM64
   compiler pragma indicates the platform added to the include files.
1. `mksnapshot` is hosted on `atom/atom`; isn't built for `arm64`.
1. `chromedriver` is hosted on `atom/atom`; isn't built for `arm64`.

## HAX

1. Need a newer version of `electron-packager` that knows about `arm64`; update
   `package.json` to `electron-packager@9.1.0`.
2. `chromedriver` is only used for tests, and isn't available from the
   `electron/electron` Releases page for `arm64` (yet). Remove it from
   `package.json`.
2. Until the `dump_syms` issue is resolved, all of the crash reporter
   infrastrucure needs to be disabled (and `minidump` needs to be removed from
   `package.json`).
3. `mksnapshot` needs to be commented out; it's possible to build a natively-
   hosted version for arm that can be used in the build process, but until we
   can figure out how to get it to work, it just slows down the build without
   doing anything useful. `electron-mksnapshot` also needs to be removed from
   `package.json`.
4. The Atom ASAR needs to be built by hand to include the assets that would
   otherwise be compiled into the snapshot. Without this, Atom is a sad panda.
   All credit to Cheng for figuring this out.