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160 lines
6.3 KiB
Markdown
160 lines
6.3 KiB
Markdown
# Rusty V8 Binding
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V8 Version: 10.7.193.3
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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 [V8's C++
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API](https://cs.chromium.org/chromium/src/v8/include/v8.h). The API should
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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 is
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not easy to use outside of Chromium. For this reason many attempts to bind to V8
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rely on pre-built binaries that are built separately from the binding itself.
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While this is simple, it makes upgrading V8 difficult, it makes CI difficult, it
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makes producing builds with different configurations difficult, and it is a
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security concern since binary blobs can hide malicious code. For this reason we
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believe it is imperative to build V8 from source code during "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
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`http://` and `https://` URLs, and file paths. The default is
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https://github.com/denoland/rusty_v8/releases/download.
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File-based mirrors are good for using cached downloads. First, point
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the 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
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or a 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 `python` in your `PATH`.
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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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The build depends on several binary tools: `gn`, `ninja` and `clang`. The
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tools 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.
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V8 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 `$GN_ARGS` environmental variable.
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Env vars used in when building from source: `SCCACHE`, `CCACHE`, `GN`, `NINJA`,
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`CLANG_BASE_PATH`, `GN_ARGS`
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## FAQ
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**Building V8 takes over 30 minutes, this is too slow for me to use this crate.
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What should I do?**
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Install [sccache](https://github.com/mozilla/sccache) or
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[ccache](https://ccache.dev/). Our build scripts will detect and use them. Set
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the `$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
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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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In the limit we would like to auto-generate bindings. We have actually started
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down this route several times, however due to many eccentric features of the V8
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API, this has not proven successful. Therefore we are proceeding in a
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brute-force fashion for now, focusing on solving our stated goals first. We hope
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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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