commit b113fffb65a002accf53724e5d57110ad215b5f7
author Daco Harkes <dacoharkes@google.com> Mon Oct 03 12:25:08 2022 +0000
committer Commit Queue <dart-scoped@luci-project-accounts.iam.gserviceaccount.com> Mon Oct 03 12:25:08 2022 +0000
tree dc5eecf74a3933695cc0b7b946c1eabdc0eee098
parent 2c3b2e2c4590a423f0640d817db073de2d33d111

Reland "[vm/ffi] Throw on returning `Error` in `Handle`"

Fix: Check handle contents for Smi.
Closes: https://github.com/flutter/flutter/issues/112726

Orignal CL description:

Makes `Dart_Handle` FFI returns behave as the following snippet:

```
Dart_Handle ExampleSnippet() {
  Dart_Handle result = ...;
  if (Dart_IsError(result)) {
    Dart_PropagateError(result);
  }
  return result;
}
```

Also makes FFI consistent with Dart_NativeFunctions, which will
automatically throw upon return if Dart_SetReturnValue set the result
to an error.

`UnhandledExceptions` cannot flow out into Dart generated code. So,
the implementation needs to be in `FfiCallInstr::EmitNativeCode`.

Using `Dart_IsError` is slow compared to a machine code class id
check. So, we should do the handle unwrapping and class id check in
machine code.

Unwrapping Handles in machine code is only safe when the GC is
guaranteed to not run: Either (1) in `kThreadInGenerated`, or (2) in
`kThreadInNative`, but only when transitioned into safepoint. So, the
handle cannot be unwrapped immediately after the FFI call in machine code. We first need to transition back to generated.

This means we need to transition again to native to do the actual
`Dart_PropagateError` call. We can do so without the stub in JIT
because we never return with normal control flow.

Performance impact of this change is within benchmark noise in both
JIT and AOT.
Size impact is 42 bytes on x64, which is 10% in AOT and 12% in JIT.

For more numbers see: go/dart-ffi-handle-error

TEST=runtime/bin/ffi_test/ffi_test_functions_vmspecific.cc
TEST=tests/ffi/vmspecific_handle_test.dart

Closes: https://github.com/dart-lang/sdk/issues/49936
Change-Id: Id8edfd841a7d6246438386007d83747868a0a151
Cq-Include-Trybots: luci.dart.try:vm-canary-linux-debug-try,vm-ffi-android-debug-arm64c-try,vm-ffi-android-debug-arm-try,vm-kernel-gcc-linux-try,vm-kernel-linux-debug-x64-try,vm-kernel-linux-debug-x64c-try,vm-kernel-msvc-windows-try,vm-kernel-optcounter-threshold-linux-release-x64-try,vm-kernel-precomp-asan-linux-release-x64-try,vm-kernel-precomp-linux-debug-x64-try,vm-kernel-reload-linux-debug-x64-try,vm-kernel-reload-rollback-linux-debug-x64-try,vm-kernel-tsan-linux-release-x64-try,vm-kernel-win-debug-x64-try,vm-kernel-win-debug-ia32-try,vm-precomp-ffi-qemu-linux-release-arm-try,vm-precomp-ffi-qemu-linux-release-riscv64-try,vm-kernel-linux-debug-ia32-try,vm-kernel-mac-release-arm64-try,vm-kernel-precomp-win-debug-x64c-try
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/262342
Reviewed-by: Martin Kustermann <kustermann@google.com>
Auto-Submit: Daco Harkes <dacoharkes@google.com>
Commit-Queue: Daco Harkes <dacoharkes@google.com>