In order to be able to build V8 from scratch on Linux/Mac for x64 please heed the following steps:

Getting the V8 source TL;DR

More in-depth information can be found here.

1. Install Git

2. Install depot_tools

3. Update depot_tools by executing the following into your terminal/shell:

   gclient
   

4. Go into the directory where you want to download the V8 source into and execute the following in your terminal/shell:

   fetch v8
   cd v8
   

Don’t simply git clone the V8 repository!

Building V8 TL;DR

More in-depth information can be found here.

1. For macOS: install Xcode and accept its license agreement. (If you’ve installed the command-line tools separately, remove them first.)

2. Make sure that you are in the V8 source directory. If you followed every step up until step 4 above, you’re already at the right location.

3. Download all the build dependencies by executing the following in your terminal/shell:

   gclient sync
   

4. Generate the necessary build files by executing the following in your terminal/shell:

   tools/dev/v8gen.py x64.release
   

5. Compile the source by executing the following in your terminal/shell:

   ninja -C out.gn/x64.release
   

6. Run the tests by executing the following in your terminal/shell:

   tools/run-tests.py --gn