build V8 on mac

// v8 的 builtin 部分由编译中间产物 mksnapshot 程序生成 // 源代码是 js ？ 跟 firefox 一样

代码只在V8的编译阶段由mksnapshot程序执行，执行后会产出机器码（JIT），然后mksnapshot程序把生成的机器码dump下来放到汇编文件embedded.S里，编译进V8运行时（相当于用JIT编译器去AOT）。

https://gist.github.com/kevincennis/0cd2138c78a07412ef21

https://github.com/v8/v8/wiki/Building-from-Source

Prerequisites

• Install Xcode (Avaliable on the Mac App Store)
• Install Xcode Command Line Tools (Preferences > Downloads)
• Install depot_tools
• git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git
• sudo nano ~/.bash_profile
• Add export PATH=/path/to/depot_tools:"$PATH" (it's important that depot_tools comes first here)
• source ~/.bash_profile
• From the directory you want to install V8 into, run gclient

Build V8

• fetch v8
• cd v8
• gclient sync
• gclient config https://chromium.googlesource.com/v8/v8
• tools/dev/v8gen.py x64.optdebug
• ninja -C out.gn/x64.optdebug (prepare for lots of fan noise)

I'd also recommend adding these to your .bash_profile:

• sudo nano ~/.bash_profile
• Add alias d8=/path/to/v8/repo/out.gn/x64.optdebug/d8
• Add alias tick-processor=/path/to/v8/repo/tools/mac-tick-processor
• Add export D8_PATH="/path/to/v8/repo/out.gn/x64.optdebug"
• source ~/.bash_profile