V8编译是个比较麻烦的事情，不仅是下载、编译的过程，不同系统、不同编译器、不同C++版本都可能会出现不同的问题。之前编译的时候没有记录步骤，这次简单记录一下编译V8的过程，我的工作目录是/code/v8_code/。

1 编译V8

1 下载工具：git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git
2 执行export PATH=$PATH:/code/v8_code/depot_tools，后续执行命令用到。
3 gclient config https://chromium.googlesource.com/v8/v8.git。
4 执行gclient sync (成功后当前目录下多一个v8目录，这时候有depot_tools和v8两个目录)
5 执行命令：alias gm=/code/v8_code/v8/tools/dev/gm.py，然后cd v8进入v8源码目录。
6 执行gm x64.release，编译成功，新建一个hello.js，执行out/x64.release/d8 hello.js就看到相应输出，或者执行out/x64.release/d8进入互动模式。

2 编译V8为静态库

执行alias v8gen=/code/v8_code/v8/tools/dev/v8gen.py，v8源码目录执行v8gen x64.release.sample生成配置文件，执行ninja -C out.gn/x64.release.sample v8_monolith编译静态库。

3 使用V8

我们可以在自己的项目里使用V8，这个已经有不少的例子，Node.js就是典型的例子，不过Node.js比较复杂，不利于快速理解如何使用V8，其实V8静态库和其他的静态库是一样，下面以V8的hello-world为例子，看看如何使用V8。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>#include "include/libplatform/libplatform.h"
#include "include/v8-context.h"
#include "include/v8-initialization.h"
#include "include/v8-isolate.h"
#include "include/v8-local-handle.h"
#include "include/v8-primitive.h"
#include "include/v8-script.h"int main(int argc, char* argv[]) {// Initialize V8.v8::V8::InitializeICUDefaultLocation(argv[0]);v8::V8::InitializeExternalStartupData(argv[0]);std::unique_ptr<v8::Platform> platform = v8::platform::NewDefaultPlatform();v8::V8::InitializePlatform(platform.get());v8::V8::Initialize();// Create a new Isolate and make it the current one.v8::Isolate::CreateParams create_params;create_params.array_buffer_allocator =v8::ArrayBuffer::Allocator::NewDefaultAllocator();v8::Isolate* isolate = v8::Isolate::New(create_params);{v8::Isolate::Scope isolate_scope(isolate);// Create a stack-allocated handle scope.v8::HandleScope handle_scope(isolate);// Create a new context.v8::Local<v8::Context> context = v8::Context::New(isolate);// Enter the context for compiling and running the hello world script.v8::Context::Scope context_scope(context);{// Create a string containing the JavaScript source code.v8::Local<v8::String> source =v8::String::NewFromUtf8Literal(isolate, "'Hello' + ', World!'");// Compile the source code.v8::Local<v8::Script> script =v8::Script::Compile(context, source).ToLocalChecked();// Run the script to get the result.v8::Local<v8::Value> result = script->Run(context).ToLocalChecked();// Convert the result to an UTF8 string and print it.v8::String::Utf8Value utf8(isolate, result);printf("%s\n", *utf8);}const char csource[] = R"(let bytes = new Uint8Array([0x00, 0x61, 0x73, 0x6d, 0x01, 0x00, 0x00, 0x00, 0x01, 0x07, 0x01,0x60, 0x02, 0x7f, 0x7f, 0x01, 0x7f, 0x03, 0x02, 0x01, 0x00, 0x07,0x07, 0x01, 0x03, 0x61, 0x64, 0x64, 0x00, 0x00, 0x0a, 0x09, 0x01,0x07, 0x00, 0x20, 0x00, 0x20, 0x01, 0x6a, 0x0b]);let module = new WebAssembly.Module(bytes);let instance = new WebAssembly.Instance(module);instance.exports.add(3, 4);)";// Create a string containing the JavaScript source code.v8::Local<v8::String> source =v8::String::NewFromUtf8Literal(isolate, csource);// Compile the source code.v8::Local<v8::Script> script =v8::Script::Compile(context, source).ToLocalChecked();// Run the script to get the result.v8::Local<v8::Value> result = script->Run(context).ToLocalChecked();// Convert the result to a uint32 and print it.uint32_t number = result->Uint32Value(context).ToChecked();printf("3 + 4 = %u\n", number);}}// Dispose the isolate and tear down V8.isolate->Dispose();v8::V8::Dispose();v8::V8::ShutdownPlatform();delete create_params.array_buffer_allocator;return 0;
}

V8的API使用过程就是初始化V8，编译执行脚本，销毁V8。下面执行g++ -I. -Iinclude samples/hello-world.cc -o hello_world -lv8_monolith -Lout.gn/x64.release.sample/obj/ -pthread -std=c++14 -DV8_COMPRESS_POINTERS编译hello-world，执行./hello_world，看到相应输出。基本的用法就是在把V8的头文件（include目录）和静态库复制到自己的项目里，然后在项目里#include<xxx/v8.h>就可以使用了，最后编译的时候类似编译hello-world一样，通过执行指定一些目录，就可以完成编译。可以参考https://github.com/theanarkh/No.js。