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Daco Harkes 9a8508ebff [vm/ffi] FfiNative assets

Adds support for `asset: 'asset-id'` in `FfiNative`s.
Symbols in assets are resolved by
1. the provided [asset] (the bulk of this CL),
2. the native resolver set with `Dart_SetFfiNativeResolver` in
   `dart_api.h` (old behavior), and
3. the current process.

Symbols in assets are resolved by the Dart VM through the mapping
provided in the `vm:ffi:native_assets` library:
```
@pragma('vm:ffi:native-assets', {
  "linux_x64": {
    "<asset1>": [
      "absolute",
      "<absolute-path>"
    ],
    "<asset2>": [
      "relative",
      "<relative-path>"
    ],
    "<asset3>": [
      "system",
      "<system-path>"
    ],
    "<asset4>": [
      "process",
    ],
    "<asset5>": [
      "executable",
    ],
  }
})
library;
```

There are 5 asset path types. Symbols resolved in these asset types are
resolved as follows.
A. Absolute paths are dlopened, after which the symbol is looked up.
B. Relative paths are resolved relative to `Platform.script.uri`, and
   dlopened, after which the symbol is looked up.
C. System paths are treated as absolute paths. (But we might explicitly
   try to use `PATH` in the future.)
D. Symbols looked up in Process assets are looked up in the current
   process.
E. Symbols looked up in Executable assets are looked up in the current
   executable.

The native assets mapping can be provided in three ways.

X. In the invocation to `gen_kernel` with the `--native-assets`
   argument. This uses the gen_kernel entry point for compiling
   kernel.
Y. By placing a `native_assets.yaml` next to the
   `package_config.json` used by the isolate group. This works for
   `dart <source file>` and `Isolate.spawnUri(<dart source file>)`.
   This uses the kernel_service entry point for compiling kernel.
Z. By sending a String containing the native assets mapping when
   invoking the kernel_service directly from within the VM. Currently,
   only used for unit tests.

TEST=tests/ffi/native_assets/asset_*_test.dart (X)
TEST=tests/ffi/native_assets/infer_native_assets_yaml_*.dart (Y)
TEST=runtime/vm/ffi/native_assets_test.cc (Z)

The library is synthesized from yaml in pkg:vm as AST.

Design doc: go/dart-native-assets

Bug: https://github.com/dart-lang/sdk/issues/49803
Change-Id: I8bf7000bfcc03b362948efd3baf168838948e6b9
Cq-Include-Trybots: luci.dart.try:vm-ffi-android-debug-arm-try,vm-ffi-android-debug-arm64c-try,vm-precomp-ffi-qemu-linux-release-arm-try,vm-kernel-nnbd-mac-debug-arm64-try,vm-kernel-nnbd-mac-debug-x64-try,vm-kernel-win-debug-x64-try,vm-kernel-win-debug-ia32-try,vm-kernel-precomp-win-debug-x64c-try,vm-kernel-reload-linux-debug-x64-try,vm-kernel-reload-rollback-linux-debug-x64-try,vm-kernel-precomp-nnbd-linux-debug-x64-try,vm-kernel-precomp-win-debug-x64c-try,vm-kernel-precomp-nnbd-mac-release-arm64-try
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/264842
Reviewed-by: Martin Kustermann <kustermann@google.com>

2023-01-18 21:08:38 +00:00

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VM-Specific Pragma Annotations

Pragmas for general use

These pragmas are part of the VM's API and are safe for use in external code.

Pragma	Meaning
`vm:entry-point`	Defining entry-points into Dart code for an embedder or native methods
`vm:never-inline`	Never inline a function or method
`vm:prefer-inline`	Inline a function or method when possible
`vm:notify-debugger-on-exception`	Marks a function that catches exceptions, making the VM treat any caught exception as if they were uncaught. This can be used to notify an attached debugger during debugging, without pausing the app during regular execution.
`vm:external-name`	Allows to specify an external (native) name for an `external` function. This name is used to lookup native implementation via native resolver associated with the current library through embedding APIs. This is a replacement for legacy VM specific `native "name"` syntax.
`vm:invisible`	Allows to mark a function as invisible so it will not appear on stack traces.
`vm:always-consider-inlining`	Marks a function which particularly benefits from inlining and specialization in context of the caller (for example, when concrete types of arguments are known). Inliner will not give up after one failed inlining attempt and will continue trying to inline this function.

Unsafe pragmas for general use

These pragmas are available for use in third-party code but are potentially unsafe. The use of these pragmas is discouraged unless the developer fully understands potential repercussions.

Pragma	Meaning
`vm:unsafe:no-interrupts`	Removes all `CheckStackOverflow` instructions from the optimized version of the marked function, which disables stack overflow checking and interruption within that function. This pragma exists mainly for performance evaluation and should not be used in a general-purpose code, because VM relies on these checks for OOB message delivery and GC scheduling.

Pragmas for internal use

These pragmas can cause unsound behavior if used incorrectly and therefore are only allowed within the core SDK libraries.

Pragma	Meaning
`vm:exact-result-type`	Declaring an exact result type of a method
`vm:recognized`	Marking this as a recognized method

Pragmas ignored in user code

These pragma's are only used on AST nodes synthesized by us, so users defining these will be ignored.

Pragma	Meaning
`vm:ffi:native-assets`	Passing a native assets mapping to the VM

Pragmas for internal testing

These pragmas are used for inspecting or modifying internal VM state and should be used exclusively by SDK tests. They must be enabled with the --enable-testing-pragmas flag. The names of these pragmas are prefixed with "testing". Additionally, they are categorized into "safe" and "unsafe" forms: "safe" pragmas should not affect the behavior of the program and can be safely added anywhere, whereas "unsafe" pragmas may change the code's behavior or may cause the VM to crash if used improperly.

Pragma	Meaning
`vm:testing.unsafe.trace-entrypoints-fn`	Observing which flow-graph-level entry-point was used when a function was called

Flutter toString transformer pragmas

These pragmas are useful to exclude certain toString methods from toString transformation, which is enabled with --delete-tostring-package-uri option in kernel compilers and used by Flutter to remove certain toString methods in release mode to reduce size.

Pragma	Meaning
`flutter:keep-to-string`	Avoid transforming the annotated toString method.
`flutter:keep-to-string-in-subtypes`	Avoid transforming toString methods in all subtypes of the annotated class.

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