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
- 2 编译V8为静态库
- 3 使用V8
一. 编译V8
1 下载工具：
git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git
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2 执行
export PATH=$PATH:/code/v8_code/depot_tools
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后续执行命令用到。
3 执行
gclient config https://chromium.googlesource.com/v8/v8.git
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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。
二. 编译V8为静态库
执行
alias v8gen=/code/v8_code/v8/tools/dev/v8gen.py
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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
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编译静态库。
三.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;
}
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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
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编译hello-world，执行./hello_world，看到相应输出。