How to build embeddable VM runtime on iOS?

[Yifeng Wang]

Hi, I'm trying to embed Dart VM on iOS, following guides in the Embedding Dart discussion  posted by Vegorov. For now I can build the minimal VM on macOS, making it running precompiled dill files. But for iOS, I found there are no related instructions on the official build guide. I have tried using different values for target_os / dart_target_arch / target_os / target_cpu build arg, but I got invalid build configs or "architecture not supported" compile time errors. I even tried open the xcodebuild/DebugX64/all.xcodeproj file, setting the target to iOS (neither does this work).

So, how to create a static library for minimal VM on iOS? How does Flutter do this? Thanks.

[Vyacheslav Egorov]

Hi, 

Note that Kernel binaries (aka dill files) is not a viable solution for iOS outside of certain scenarios (running them requires JIT) - you would need to build precompiled runtime targeting iOS  - your only option is to build precompiled (AOT) runtime. 

Unfortunately I don't think that SDK is set for building to iOS right now. BUILDCONFIG.gn in our buildroot does not have enough stuff to enable building for iOS. 

You can compare https://github.com/dart-lang/sdk/blob/master/build/config/BUILDCONFIG.gn and https://github.com/flutter/buildroot/blob/master/build/config/BUILDCONFIG.gn

I think the simplest approach can be to use a flutter engine build environment and then you can just take AOT runtime built there and use it in your app. 

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On Thu, Nov 5, 2020 at 6:53 PM Yifeng Wang <doodl...@gmail.com> wrote:

Hi, I'm trying to embed Dart VM on iOS, following guides in the Embedding Dart discussion  posted by Vegorov. For now I can build the minimal VM on macOS, making it running precompiled dill files. But for iOS, I found there are no related instructions on the official build guide. I have tried using different values for target_os / dart_target_arch / target_os / target_cpu build arg, but I got invalid build configs or "architecture not supported" compile time errors. I even tried open the xcodebuild/DebugX64/all.xcodeproj file, setting the target to iOS (neither does this work).

So, how to create a static library for minimal VM on iOS? How does Flutter do this? Thanks.

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[Yifeng Wang]

Thanks for the suggestion, I’ve made pretty much progress porting standalone Dart VM to iOS, here are some follow-ups:

Within the Flutter’s build environment, I built a new static library containing libdartvm with no snapshot (the precompiled runtime library is also ready, but I just need a minimalist prototype for now). This library contains all symbols to run the embedder example, while two more kernel binary files are required:

* For the `vm_platform_strong.dill` , it’s inside the flutter engine’s compiled products for iOS. This works fine.

* For the `app.dill` kernel binary, I tweaked the flutter tool a little bit, then started an empty Flutter project, changed its lib/main.dart to a bare empty main function, got its compiled output (~5KB) from the CFE’s tmp output folder.

Now the question is that, when I call `Dart_LoadLibraryFromKernel` to load the `app.dill` file, I got an “Invalid kernel binary format version” error, which is a check that `vm_platform_strong.dill` passed. To be more specific, the Dart VM on iOS expects binary version 49, but the version of `app.dill` I compiled is 45.

The `vm_platform_strong.dill` that passed the check is compiled with Flutter engine’s source code, whose Dart VM version is 2.12.0-4.0.dev. But when I compile `app.dill`, the Dart VM running CFE on my Mac is v2.10.3. However, I got both of them coming from the official Flutter release (1.22.3), is this mismatch in VM version expected, or am I doing something wrong?

I think I’m much closer to a working prototype. I’d really appreciate any further advice. Thanks.

Yifeng

[Yifeng Wang]

Update: With same revision of Flutter Tool and Flutter Engine, I got the embedded VM running on iOS now. Thanks for the help!

[Randal L. Schwartz]

On Nov 11, 2020, at 9:59 PM, Yifeng Wang <doodl...@gmail.com> wrote:

Update: With same revision of Flutter Tool and Flutter Engine, I got the embedded VM running on iOS now. Thanks for the help!

does this mean it won’t be long before we get an nginx or apache plugin and get Dart seriously on the web server side?