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223 lines
8.8 KiB
Markdown
223 lines
8.8 KiB
Markdown
# Rusty V8 Binding
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V8 Version: 12.8.374.6
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[](https://github.com/denoland/rusty_v8/actions)
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[](https://crates.io/crates/v8)
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[](https://docs.rs/v8)
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## Goals
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1. Provide high quality Rust bindings to
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[V8's C++ API](https://cs.chromium.org/chromium/src/v8/include/v8.h). The API
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should match the original API as closely as possible.
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2. Do not introduce additional call overhead. (For example, previous attempts at
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Rust V8 bindings forced the use of Persistent handles.)
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3. Do not rely on a binary `libv8.a` built outside of cargo. V8 is a very large
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project (over 600,000 lines of C++) which often takes 30 minutes to compile.
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Furthermore, V8 relies on Chromium's bespoke build system (gn + ninja) which
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is not easy to use outside of Chromium. For this reason many attempts to bind
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to V8 rely on pre-built binaries that are built separately from the binding
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itself. While this is simple, it makes upgrading V8 difficult, it makes CI
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difficult, it makes producing builds with different configurations difficult,
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and it is a security concern since binary blobs can hide malicious code. For
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this reason we believe it is imperative to build V8 from source code during
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"cargo build".
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4. Publish the crate on crates.io and allow docs.rs to generate documentation.
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Due to the complexity and size of V8's build, this is nontrivial. For example
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the crate size must be kept under 10 MiB in order to publish.
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## Binary Build
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V8 is very large and takes a long time to compile. Many users will prefer to use
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a prebuilt version of V8. We publish static libs for every version of rusty v8
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on [Github](https://github.com/denoland/rusty_v8/releases).
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Binaries builds are turned on by default: `cargo build` will initiate a download
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from github to get the static lib. To disable this build using the
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`V8_FROM_SOURCE` environmental variable.
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When making changes to rusty_v8 itself, it should be tested by build from
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source. The CI always builds from source.
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## The `V8_FORCE_DEBUG` environment variable
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By default `rusty_v8` will link against release builds of `v8`, if you want to
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use a debug build of `v8` set `V8_FORCE_DEBUG=true`.
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We default to release builds of `v8` due to performance & CI reasons in `deno`.
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## The `RUSTY_V8_MIRROR` environment variable
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Tells the build script where to get binary builds from. Understands `http://`
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and `https://` URLs, and file paths. The default is
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https://github.com/denoland/rusty_v8/releases.
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File-based mirrors are good for using cached downloads. First, point the
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environment variable to a suitable location:
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# you might want to add this to your .bashrc
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$ export RUSTY_V8_MIRROR=$HOME/.cache/rusty_v8
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Then populate the cache:
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```bash
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#!/bin/bash
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# see https://github.com/denoland/rusty_v8/releases
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for REL in v0.13.0 v0.12.0; do
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mkdir -p $RUSTY_V8_MIRROR/$REL
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for FILE in \
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librusty_v8_debug_x86_64-unknown-linux-gnu.a \
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librusty_v8_release_x86_64-unknown-linux-gnu.a \
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; do
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if [ ! -f $RUSTY_V8_MIRROR/$REL/$FILE ]; then
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wget -O $RUSTY_V8_MIRROR/$REL/$FILE \
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https://github.com/denoland/rusty_v8/releases/download/$REL/$FILE
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fi
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done
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done
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```
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## The `RUSTY_V8_ARCHIVE` environment variable
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Tell the build script to use a specific v8 library. This can be an URL or a
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path. This is useful when you have a prebuilt archive somewhere:
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```bash
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export RUSTY_V8_ARCHIVE=/path/to/custom_archive.a
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cargo build
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```
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## Build V8 from Source
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Use `V8_FROM_SOURCE=1 cargo build -vv` to build the crate completely from
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source.
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The build scripts require Python 3 to be available as `python3` in your `PATH`.
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If you want to specify the exact binary of Python to use, you should use the
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`PYTHON` environment variable.
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The build also requires `curl` to be installed on your system.
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For linux builds: glib-2.0 development files need to be installed such that
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pkg-config can find them. On Ubuntu, run `sudo apt install libglib2.0-dev` to
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install them.
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For Windows builds: the 64-bit toolchain needs to be used. 32-bit targets are
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not supported.
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For Mac builds: You'll need Xcode and Xcode CLT installed. Recent macOS versions
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will also require you to pass PYTHON=python3 because macOS no longer ships with
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`python` simlinked to Python 3.
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For Android builds: You'll need to cross compile from a x86_64 host to the aarch64 or x64 android. You can use the following commands:
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```bash
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rustup target add aarch64-linux-android # or x86_64-linux-android
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V8_FROM_SOURCE=1 cargo build -vv --target aarch64-linux-android
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# or with cross
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docker build --build-arg CROSS_BASE_IMAGE=ghcr.io/cross-rs/aarch64-linux-android:0.2.5 -t cross-rusty_v8:aarch64-linux-android .
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V8_FROM_SOURCE=1 cross build -vv --target aarch64-linux-android
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```
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The build depends on several binary tools: `gn`, `ninja` and `clang`. The tools
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will automatically be downloaded, if they are not detected in the environment.
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Specifying the `$GN` and `$NINJA` environmental variables can be used to skip
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the download of gn and ninja. The clang download can be skipped by setting
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`$CLANG_BASE_PATH` to the directory containing a `llvm`/`clang` installation. V8
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is known to rely on bleeding edge features, so LLVM v8.0+ or Apple clang 11.0+
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is recommended.
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Arguments can be passed to `gn` by setting the `$GN_ARGS` environmental
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variable.
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Env vars used in when building from source: `SCCACHE`, `CCACHE`, `GN`, `NINJA`,
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`CLANG_BASE_PATH`, `GN_ARGS`
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## FAQ
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**Building V8 takes over 30 minutes, this is too slow for me to use this crate.
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What should I do?**
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Install [sccache](https://github.com/mozilla/sccache) or
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[ccache](https://ccache.dev/). Our build scripts will detect and use them. Set
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the `$SCCACHE` or `$CCACHE` environmental variable if it's not in your path.
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**What are all these random directories for like `build` and `buildtools` are
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these really necessary?**
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In order to build V8 from source code, we must provide a certain directory
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structure with some git submodules from Chromium. We welcome any simplifications
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to the code base, but this is a structure we have found after many failed
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attempts that carefully balances the requirements of cargo crates and GN/Ninja.
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**V8 has a very large API with hundreds of methods. Why don't you automate the
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generation of this binding code?**
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We have actually started down this route several times, however due to many
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eccentric features of the V8 API, this has not proven successful. Therefore we
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are proceeding in a brute-force fashion for now, focusing on solving our stated
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goals first. We hope to auto-generate bindings in the future.
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**Why are you building this?**
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This is to support [the Deno project](https://deno.land/). We previously have
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gotten away with a simpler high-level Rust binding to V8 called
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[libdeno](https://github.com/denoland/deno/tree/32937251315493ef2c3b42dd29340e8a34501aa4/core/libdeno).
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But as Deno has matured we've found ourselves continually needing access to an
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increasing amount of V8's API in Rust.
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**When building I get unknown argument: '-gno-inline-line-tables'**
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Use `export GN_ARGS="no_inline_line_tables=false"` during build.
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**My program crashes when initializing on non-main thread**
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Initializing V8 on a non-main thread with the CPUs PKU feature enabled might
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lead to crashes. You can work around this problem by using
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`v8::new_unprotected_default_platform`.
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See https://github.com/denoland/rusty_v8/issues/1381
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## Download cache
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The v8 archives used for linking in prebuilt mode can be cached to avoid
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re-downloading archives when switching between branches that otherwise change
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the current rusty_v8 version.
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To populate the cache by hand, you'll need to place the files in the appropriate
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location in your `.cargo` folder. Running `cargo build -v -v` will print two
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lines that you can use to determine the correct file and cache location:
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```
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[v8 0.87.0] static lib URL: https://github.com/denoland/rusty_v8/releases/download/v0.87.0/librusty_v8_release_aarch64-apple-darwin.a.gz
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[v8 0.87.0] Looking for download in '"/Users/<name>/.cargo/.rusty_v8/https___github_com_denoland_rusty_v8_releases_download_v0_87_0_librusty_v8_release_aarch64_apple_darwin_a_gz"'
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```
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Given the above log output, use `curl` to download the file like so:
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```
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curl -L https://github.com/denoland/rusty_v8/releases/download/v0.87.0/librusty_v8_release_aarch64-apple-darwin.a.gz >
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/Users/<name>/.cargo/.rusty_v8/https___github_com_denoland_rusty_v8_releases_download_v0_87_0_librusty_v8_release_aarch64_apple_darwin_a_gz
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```
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## For maintainers
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**Cut a release**
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Create a PR to bump the release version (e.g.
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https://github.com/denoland/rusty_v8/pull/1415).
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Create a new release/tag after the bump PR is landed. CI will publish the crate
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and upload release binaries. You will need to manually upload binary archives
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for M1 build.
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```
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$ V8_FROM_SOURCE=1 cargo build
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$ V8_FROM_SOURCE=1 cargo build --release
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```
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