commit 4b66657b984d41c34250e1e7b80030fcfb6a82a8
author Daco Harkes <dacoharkes@google.com> Thu Apr 25 10:06:16 2024 +0000
committer Commit Queue <dart-scoped@luci-project-accounts.iam.gserviceaccount.com> Thu Apr 25 10:06:16 2024 +0000
tree 9b74d2eb0cd706182ce24a1eaa4f7fe2bb43bac7
parent 8c1475c6c26f47ccba46f62afbd7d8599a992464

[vm/ffi] `address` of operator for FFI leaf calls

During FFI leaf calls, the Dart GC will not run. This means that we
can pass pointers into `TypedData` to FFI calls that take `Pointer`
arguments.

After this CL, we have three types of arguments that can flow into
`Pointer` argument in an FFI call:
* `Pointer`.
* `TypedData`: Any typed data including views.
* `_Compound`: A TypedData/Pointer and an offset in bytes.

The is only possible for `@Native external` functions, `asFunction`
does not support passing in `TypedData`. (See related GitHub issues
for discussion. TLDR: FFIgen should generate bindings without config.)

`.address` expressions on `TypedData` and `Array` elements do _not_
introduce bounds checks, even though `TypedData` and `Array` have
bounds information. E.g. `ffiNative(Uint8List(10)[20].address)` does
not throw.

Implementation details:

The CFE analyzes call-sites to `@Native external` functions. If the
arguments are `.address` expressions, it transforms the call site to
pass the compound or `TypedData`. If an additional offset needs to be
applied, the CFE constructs a new `_Compound` with the correct offset
in bytes.

The CFE then also creates a new `@Native external` function which have
`TypedData`s and `_Compound`s parameters. To avoid name clashes, these
functions are postfixed with `#` and `P`, `T`, or `C` for each Pointer
parameter.

TEST=pkg/vm/testcases/transformations/ffi/address_of_*

In the VM, `TypedData` arguments are passed as tagged values, and the
address is loaded inside the `FfiCallInstr`. `_Compound` arguments
turn into two IL definitions, one for the `TypedDataBase` (tagged),
and one for the offset in bytes (unboxed). The address is then loaded
inside the `FfiCallInstr` and the offset in bytes is applied.

Adding the offset in bytes required an extra temp register for ia32.
Also, it uncovered that the temp register in arm32 was conflicting
with the argument registers. However, TMP should suffice instead.

TEST=tests/ffi/address_of_array_generated_test.dart
TEST=tests/ffi/address_of_struct_generated_test.dart
TEST=tests/ffi/address_of_typeddata_generated_test.dart

Closes: https://github.com/dart-lang/sdk/issues/44589
Closes: https://github.com/dart-lang/sdk/issues/54771

CoreLibraryReviewExempt: VM only, unsupported in dart2wasm
Change-Id: I01fb428cfd6f9096a34689c2819c124a8003cb6b
Cq-Include-Trybots: dart/try:vm-aot-android-release-arm64c-try,vm-aot-android-release-arm_x64-try,vm-aot-linux-debug-x64-try,vm-aot-linux-debug-x64c-try,vm-aot-mac-release-arm64-try,vm-aot-mac-release-x64-try,vm-aot-obfuscate-linux-release-x64-try,vm-aot-optimization-level-linux-release-x64-try,vm-aot-win-debug-arm64-try,vm-aot-win-debug-x64c-try,vm-aot-win-release-x64-try,vm-appjit-linux-debug-x64-try,vm-asan-linux-release-x64-try,vm-checked-mac-release-arm64-try,vm-eager-optimization-linux-release-ia32-try,vm-eager-optimization-linux-release-x64-try,vm-ffi-android-debug-arm64c-try,vm-ffi-qemu-linux-release-arm-try,vm-ffi-qemu-linux-release-riscv64-try,vm-linux-debug-ia32-try,vm-linux-debug-x64-try,vm-linux-debug-x64c-try,vm-mac-debug-arm64-try,vm-mac-debug-x64-try,vm-msan-linux-release-x64-try,vm-reload-linux-debug-x64-try,vm-reload-rollback-linux-debug-x64-try,vm-ubsan-linux-release-x64-try,vm-win-debug-arm64-try,vm-win-debug-x64-try,vm-win-debug-x64c-try,vm-win-release-ia32-try
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/360882
Reviewed-by: Jens Johansen <jensj@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Reviewed-by: Martin Kustermann <kustermann@google.com>
Commit-Queue: Daco Harkes <dacoharkes@google.com>
Reviewed-by: Tess Strickland <sstrickl@google.com>
Reviewed-by: Lasse Nielsen <lrn@google.com>