define – j2i.net

Compiling V8 on Windows (version 13.7.9)

I had an idea for an application that would be using some native code, but also needed to be customizable through changing JavaScript. v8 was the first choice for a JavaScript engine to integrate. It is the most popular JavaScript engine. Having modified Chromium before, (V8 is part of the Chromium source code) I thought this would be more of the same procedures that I had followed before. That’s not the case. The last time I worked with this code, it was with Microsoft Visual C/C++. But back in September 2024 the V8 group followed Chromium’s lead and removed support for MSVC. The change makes sense, they wanted to reduce the various compiler nuances and hacks that they had to account for when updating the source code. The old procedure I used was not going to work. I had to figure out how to build V8 again.

Appreciation for the V8 Team

I want to take a moment to thank the V8 team for their effort. I’ve not interacted with them directly myself. But from reading in the Google Group for V8, I’ve seen that they’ve been responsive to questions that others have asked, and I’ve found their responses helpful. If/when I do interact with them directly I want to remember to express my appreciation. If you interact with them, I encourage doing the same.

Why doesn’t Google Just Distribute a Precompiled Version

The first time I used V8, I questioned why Google didn’t just make a precompiled version available. After working in it myself, I can better appreciate why one might not want to do that. There are a log of variations in build options. It simply just isn’t practical.

The Build Script

Because the build procedure is expected to change over time, I’ve made the rare decision to call out the V8 version that I’m working with in the title of this post. This procedure might not work with earlier or later versions of V8. Consider what version of v8 that you wish to build. The more significant the difference in that version number and what I’ve posted here (13.7.9) the higher the chance of this document being less applicable.

As I did with the AWS C++ SDK and the Clang compiler, I wanted to script the compilation process and add the script to my developer setup scripts. The script is in a batch file. While I would have preferred to use PowerShell, the build process from Google uses batch files. Yes, you can call a batch file from PowerShell. But there are differences in how batch files execute from PowerShell vs the command prompt.

Installing the Required Visual Studio Components

If you are building the V8 source code, you probably already have Visual Studio 17 20222 installed with C++ support. You’ll want to add support for the Clang compiler and additional tools. While you could start the Visual Studio installer and select the required components, in my script I’ve included a command to invoke the installer with those components selected. You’ll have to give it permission to run. If you want to invoke this command yourself to handle putting the components in place, here it is.

pushd "C:\Program Files (x86)\Microsoft Visual Studio\Installer\"
vs_installer.exe install --productid Microsoft.VisualStudio.Product.Community --ChannelId VisualStudio.17.Release --add Microsoft.VisualStudio.Workload.NativeDesktop  --add Microsoft.VisualStudio.Component.VC.ATLMFC  --add Microsoft.VisualStudio.Component.VC.Tools.ARM64 --add Microsoft.VisualStudio.Component.VC.MFC.ARM64 --add Microsoft.VisualStudio.Component.Windows10SDK.20348  --add Microsoft.VisualStudio.Component.VC.Llvm.Clang --add Microsoft.VisualStudio.Component.VC.Llvm.ClangToolset --add Microsoft.VisualStudio.ComponentGroup.NativeDesktop.Llvm.Clang	 --includeRecommended
popd

Depot Tools

In addition to the source code, Google makes available a collection of tools and utilities that are used in building V8 and Chromium known as “Depot Tools.” These tools contain a collection of executables, shell scripts, and batch files that help abstract away the differences in operating systems, bringing the rules and procedures to be closer together.

Customizing my Script

For the script that I’ve provided, there are a few variables in it that you probably want to modify. The drive on which the code will be downloaded, the folders into which the code and depot tools will be placed, and the path to a temp folder are all specified in the batch file. I’ve selected paths that result in c:\shares\projects\google being the parent folder of all of these, with the v8 source code being placed in c:\shares\projects\google\v8. If you don’t like paths, update the values that are assigned to drive, ProjectRoot, TempFolder, and DepotFolder.

Running the Script

The Happy Path

If all goes well, a developer opens their Visual Studio Developer Command Prompt, invokes the script, and is presented with the Visual Studio Installer UI a few moments later. The user would OK/Next through the isntaller. After that, the Windows SDK isntaller should present and the user does the same thing. The user could then walk away and when they come back, they should have compiled V8 libraries for debug and release modes for x64 and ARMS64.

A walkthrough of what happens

The script I provided must be run from a Visual Studio Developer command prompt. Administrative level priviledges is not needed for the script, but it will be requested during the application of the Visual Studio changes. Because elevated processes don’t run as a child process of the build script, the script has no way of knowing when the isntallation completes. It will pause when the Visual Studio Installer is invoked and won’t continue until the user presses a key in the command window. Once the script continues, it will download the Windows SDK and invoke the installer. Next, it clones Depot Tools folder from Google. After cloning Depot Tools, the application gclient needs to be invoked at least once. Thsi script will invoke it.

With gclient initialized, it is now invoked to download the V8 source code and checkout a specific version. Then the builds get kicked off. The arguments for the builds could be passed as command line argumens, or they could be placed in a file named args.gn. I’ve placed configuration files for the 4 build variations with this build script.

V8 Hello World

Just as I did with the AWS C++ SDK script, I’ve got a “Hello World” program that doesn’t do anything significant. It’s purpose is to stand as a target for validating that the SDK successfully compiled and that we can link to it. The Hello World source is frp, pme pf the programs that Google provides. I’ve placed it in a Visual Studio project. If you are using same settings that I used in my build script, you will be able to compile this program without making any modifications. Nevertheless, I’ll explain what I had to do.

// v8monolithlinktest.cpp : This file contains the 'main' function. Program execution begins and ends there.
//
#include <libplatform/libplatform.h>
#include <v8-context.h>
#include <v8-initialization.h>
#include <v8-isolate.h>
#include <v8-local-handle.h>
#include <v8-primitive.h>
#include <v8-script.h>

int main(int argc, char** argv)
{
	v8::V8::InitializeExternalStartupData(argv[0]);
	std::unique_ptr<v8::Platform> platform = v8::platform::NewSingleThreadedDefaultPlatform();
	v8::V8::InitializePlatform(platform.get());
	v8::V8::Initialize();
	v8::Isolate::CreateParams create_params;
	v8::V8::Dispose();
	v8::V8::DisposePlatform();
	delete create_params.array_buffer_allocator;
	return 0;
}

I made a new C++ Console program in Visual Studio. The program needs to know the folder that has the LIB file and header files. The settings for binding to the C/C++ runtime must also be consistent between the LIB and out program. I will only cover configuring the program for debug mode. Configuring for release will involve different values for a few of the settings.

Right-click on the project and select “Properties.” Navigate to the options C++ -> Command Line on the left On the text box on the right labeled Additional Options enter the argument /Zc:__cplusplus (that command contains 2 underscores). This is necessary because, for compatibility reasons, Visual Studio will report as using an older version of C++. The V8 source code has macros within it that will intentionally cause the compilation to fail if the compiler doesn’t report as having C++ 20 or newer. Now, go to the setting C++ -> Language -> C++ Language Standard. Change it to C++ 20. Go to C++ -> General -> Additional Include Directories. In the drop-down on the right side, select “Edit.” Add a new path. If you’ve used the default settings, the new path will be c:\shares\projects\google\v8\include. Finally, go to C++ -> Linker -> General. For “Additional Library Directories” select the dropdown to click on the “Edit” option. Enter the path c:\shares\projects\google\v8\out\x64.debug.

With those settings applied, if you compile now the compilation will fail. Let’s examine the errors that come abck and why.

Unresolved External Symbols

You might get Unresolved External symbol errors for all of the V8 related functions. Here is some of the error output.

v8monolithlinktest.obj : error LNK2019: unresolved external symbol “class std::unique_ptr> __cdecl v8::platform::NewSingleThreadedDefaultPlatform(enum v8::platform::IdleTaskSupport,enum v8::platform::InProcessStackDumping,class std::unique_ptr>)” (?NewSingleThreadedDefaultPlatform@platform@v8@@YA?AV?$unique_ptr@VPlatform@v8@@U?$default_delete@VPlatform@v8@@@std@@@std@@W4IdleTaskSupport@12@W4InProcessStackDumping@12@V?$unique_ptr@VTracingController@v8@@U?$default_delete@VTracingController@v8@@@std@@@4@@Z) referenced in function main
1>v8monolithlinktest.obj : error LNK2019: unresolved external symbol “public: __cdecl v8::Isolate::CreateParams::CreateParams(void)” (??0CreateParams@Isolate@v8@@QEAA@XZ) referenced in function main

These are because you’ve not linked to the the necessary V8 library. This can be resolved through the project settings or through the source code. I’m going to resolve it through the source code with preprocessor directives. The #pragma comment() preprocessor maco is used to link to LIB files. Let’s link to v8_monolith.lib by placing this somewhere in the cpp files.

#pragma comment(lib, "v8_monolith.lib")

If you compile again, you’ll still get an unresolved externals error. This one isn’t about a V8 function, though.

1>v8_monolith.lib(time.obj) : error LNK2019: unresolved external symbol __imp_timeGetTime referenced in function "class base::A0xE7D68EDC::TimeTicks __cdecl v8::base::`anonymous namespace'::RolloverProtectedNow(void)" (?RolloverProtectedNow@?A0xE7D68EDC@base@v8@@YA?AVTimeTicks@12@XZ)
1>v8_monolith.lib(platform-win32.obj) : error LNK2001: unresolved external symbol __imp_timeGetTime
1>C:\Users\Joel\source\repos\v8monolithlinktest\x64\Debug\v8monolithlinktest.exe : fatal error LNK1120: 1 unresolved externals

The code can’t find the library that contains the function used to get the time. Linking to WinMM will take care of that. We another an other #pragma comment() preprocessor directive.

#pragma comment(lib, "WinMM.lib")

Here’s another compiler error that will be repeated several hundred times.

1>libcpmtd0.lib(xstol.obj) : error LNK2038: mismatch detected for '_ITERATOR_DEBUG_LEVEL': value '0' doesn't match value '2' in v8monolithlinktest.obj

The possible range for _ITERATOR_DEBUG_LEVEL is from 0 to 2 (inclusive). This error is stating that the V8 LIB has this constant defined to 0 while in our code, it is defaulting to 2. We need to #define it in our code before any of the standard libraries are included. It is easiest to do this at the top of the code. I make the following the first line in my source code.

#define _ITERATOR_DEBUG_LEVEL 0

The code will now compile. But when you run it, there are a few failures that you will encounter. I’ll just list the errors here. The code terminates when it encounters one of these errors. You would only be able to observe one for each run. The next error would be encountered after you’ve addressed the previous one. These failures are from the code checking to ensure that your runtime settings are compatible with the compile time settings. Some settings can only be set at compile time. If the V8 code and your code have diffeerent expectations, there’s no way to resolve the conflic. Thus the code fails to force the developer to resolve the issue.

Embedder-vs-V8 build configuration mismatch. On embedder side pointer compression is DISABLED while on V8 side it's ENABLED.

Embedder-vs-V8 build configuration mismatch. On embedder side V8_ENABLE_CHECKS is DISABLED while on V8 side it's ENABLED.

These are also resolved by #define directives before the relevant includes. These values must be also be consistent with values that were used when compiling the V8 library. The lines that resolve these errors follow.

#define V8_COMPRESS_POINTERS
#define V8_ENABLE_CHECKS true

I’ve mentioned a few times values for options within the V8 library. Those values come from the arguments that were passed when V8 was built. Let’s take a look at one of the args.gn files that contains these arguments.

dcheck_always_on = false
is_clang = true
is_component_build = false
is_debug = true
symbol_level=2
target_cpu = "x64"
treat_warnings_as_errors = false
use_custom_libcxx = false
# use_glib = true
# v8_enable_gdbjit = false
v8_enable_i18n_support = true
v8_enable_pointer_compression = true
v8_enable_sandbox = false
v8_enable_test_features = false
v8_monolithic = true
v8_static_library = true
v8_target_cpu="x64"
v8_use_external_startup_data = false
# cc_wrapper="sccache"

I won’t explain everythin within these settings, but there are a few items to call out.

v8_monolith – this option causes all of the functionality to be compiled into a single lib.
use_custom_libxx – when true, the code will use a custom C++ library from google. When false, the code will use a standard library. Always set this to false.
is_debug – set to true for debug builds, and false for release builds
v8_static_library – When true, the output contains libs to be statically linked to a program. When false, dlls are produced that must be distributed with the program.

Many of these settings have significant or interesting impacts. The details of what each one doesn’t isn’t discussed here. I’m assuming that most people that are reading this are just getting started with V8. The details of each of these build options might not be at the top of your list if you are just getting started. For some of these settings, Google has full page documents on what the settings do. The two most important settings are the v8_monolith and the is_debug setting. v8_monolith will package all of the functionality for v8 in a single large lib. The one I just compiled is about 2 gigabytes. If this option isn’t used, then the developer must makes sure that all of the necessary DLLs for the program are collected and deployed with their program.

Enabling is_debug (especially with a symbol level of 2) let’s you step into the v8 code. Even if you trust that the v8 code works fine, it is convinient to be able to step into v8.

Distributing the Outputs

After you’ve made a build and are happy with it, you want to distribute it to either other developers or archive it for yourself. Since this example makes the monolithic build, the only files that are needed are a single lib file (though very large) and the header files. You can find the V8 libs in in v8\out\x64.release\v8_monolith.lib and v8\out\x64.debug\v8_monolith.lib. Note that these files have the same name and are aonly separated by their folder. When you archive the lib, you may want to archive the args.gn file that was used to make it. It can serve as documentation for a developer using the lib. You also need the include folder from v8\includes. That’s all that you need. Because I might want to have more than one version of the V8 binaries on my computer, I’ve also ensured that the version number is also part of the file path.

Finding Resources

I looked around to try to find a good book on the V8 system, and I can’t find any. It makes sense why there are no such books. It is a rapidly evolving system. The best place I think you will find for support is the V8 Google Groups. Don’t just go there when you need help, it may be good to randomly read just to pick up information you might not have otherwise. There is also v8.dev for getting a great surface level explanation of the system. Note that some of the code in the examples on their site are a bit out-of-date. I tried a few and found that some minor adjustments are needed for some code exables to work.

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Setting Up for Pi Pico Development (2025)

In a previous post, I mentioned that I was re-introducing myself to development for the Pi Pico. The Pico is a microcontroller, often compared to an Arduino, that can be programmed from a Linux, Mac, or Windows machine. The Pico is based on the RP2040 chip. This is an ARM based Cortex-M0 dual core processor, generally running between 125 and 133 MHz. It has 264 KB of SRAM, 2 MB of flash memory, 26 general purpose IO pins, some of which support additional functionality. The other functionality overlaid on these pins includes

2 UART pins
2 SPI controllers
2 I2C controllers
16 PWM channels

There are several development boards that use the RP2040. Collectively, I generically refer to all of these as Pico. It is a bit easier to say then “RP2040 based board.”

A smaller RP2040 based board by WaveShare

I already had a few machines setup for development for the Raspberry Pi Pico. While that procedure still works, as do those development machines, I was recently reintroducing myself to Pico development. I started with a clean installation and went to the currently published instructions for setup. The more recent instructions are a lot easier to follow; there are less dependencies on manually setting paths and downloading files. The easier process is made possible through a Visual Studio Code plugin. This extension, which is still labeled as a zero version at the time that I am making this post (0.17.3) adds project generation and sample code along with scripts and automations for common tasks. To get started, just Install the Raspberry Pi Pico Visual Studio Code Extension. Once it is installed, you’ll have a new icon on the left pane of VS Code for Pico related tasks.

The first time you do anything with this icon, expect it to be slow. It installs the other build tools that it needs on-demand. I prefer to use the C++ build tools. Most of what I write here will be focused on that. I’ll start with creating a new C++ project. Double-clicking on “New C/C++ Project” from the Pico tools panel gets the process started.

This will only be a “Hello World” program. We will have the Pico print a message to a serial port in a loop. The new project window lets us specify our target hardware, including which hardware features that we plan to use. Selecting a feature will result in the build file for the project linking to necessary libraries for that feature and adding a small code sample that access that feature. Select a folder in which the project folder will be created, enter a project name, and check the box labeled “Console over USB.” After selecting these options, click on the “Create” button.

This is the part that takes a while the first time. A notification will show in VS Code stating that it is installing the SDK and generating the project. The wait is only a few minutes. While this is executing, it is a good time to grab a cup of coffee.

When you get back, you’ll see VS Code welcome you with a new project. The default new project prints “Hello, world!\n” in a loop with a 1 second delay. Grab your USB cable and a Pico. We can immediately start running this program to see if the build chain works. On the Pico, there’s a button. Connect your USB cable to your computer, then connect the Pico, making sure you are holding down this button as you connect it. The Pico will show up on your computer as a writable drive. After you’ve done this, take note of which serial ports show up on your computer. In my case, I’m using Windows, which shows that Com1 is the only serial port. In VS Code, you now have several tasks for your project that you can execute. Double-click on Run Project (USB). The code will compile, deploy to the Pico, and the Pico will reboot and start running the code.

Check to see what serial ports exist on your computer now. For me, there is a new port named Com4. Using PuTTY, I open Com4 at a baud rate of 115,200. The printed text starts to show there.

Using the USB UART for output is generally convenient, but at time you may want to use the USB for other features. The USB output is enabled or disabled in part through a couple of lines in the CMakeList.txt file.

pico_enable_stdio_uart(HelloWorldSample 0)
pico_enable_stdio_usb(HelloWorldSample 1)

The 1 and 0 can be interpreted as meaning enable and disable. Swap these values and run the project again by disconnecting the Pico, reattach while pressing the button, and then selecting the Run Project (USB) option from VS Code. When you run the code this time, the output is being transmitted over GPIO pins 0 and 1. But how do we read this?

FTDI USB

FTDI is the name of an integrated circuit manufacturer. For microcontroller interfacing, you might often see people refer to “FTDI USB” cables. These are USB devices that have 3 or 4 pins for connecting to other serial devices. These are generally cheaply available. The pins that we care about will be labeled GND (Ground), TX (Transmit), and RX (Receive). The transmit pin on one end of a serial exchange connects to the receive end on the other, and vice versa. On the Pico, the default pins used for uart0 (the name of our serial port) are GP0 for TX and GP1 for RX. When connecting an FTDI device, connect the FTDI’s RX to the Pico’s TX on GPO, then the FTDI’s TX to the Pico’s RX (on GP1), and finally the FTDI’s ground to the Pico’s ground.

GPIO – Setting a Pin

Many, Pico’s have a LED attached to one of the pins that is immediately available for test programs. While many do, not all do. On the Pi Pico and Pi Pico 2, GPIO 25 is connected to a LED. On the Pi Pico W, the LED is connected to the WiFi radio and not the RP2040 directly. For uniformity, I’ll drive an external LED. I’ve taken a LED and have it connected in series with a resistor. 220Ω should be a sufficient value for the resistor. I’m connecting the longer wire of the LED to GP5 and the shorter pin to ground.

In the code, the pin number is assigned to a #define. This is common, as it makes the code more flexible for others that may be using a different pin assignment. Before we can start writing to the pin, we need to gall an initialize function for the pin number named gpio_init(). After the initialization, we need to set the pin to be either in input or output mode. Since we are going to be controlling a LED, this needs to be output mode. This is done with a call to gpio_set_dir() (meaning “set direction”) passing the pin number as the first argument, and the direct (GPIO_IN or GPIO_OUT) as the second argument. For writing, we use GPIO_OUT. With the pin set to output, we can drive the pin to a high or low state by calling gpio_put(). The pin number is passed in the first argument, and a value indicating whether it should be in a high or low state in the second argument. A zero value is considered low, while a non-zero value is considered high. To make it apparent that the LED is being driven by our control of the pin (and not that we just happened to wire the LED to a pin that is always high) we will turn the light on and off once per second. In a loop, we will turn the light on, wait half a second, turn the light off, and wait again.

#include <stdio.h>
#include "pico/stdlib.h"

#define LED_PIN 5
int main()
{
    stdio_init_all();
    gpio_init(LED_PIN);
    gpio_set_dir(LED_PIN, GPIO_OUT);

    while (true) {
        gpio_put(LED_PIN, 1);   
        sleep_ms(500);
        gpio_put(LED_PIN, 0);
        sleep_ms(500);
    }
}

When we run the code now, we should see the light blink.

Up Next: Programmable IO – The Processor within the Processor

While the GPIO system can be manipulated by the main processor core, there are also smaller processors on the silicon that exist just for controlling the GPIO. These processors have a much smaller reduced set but are great for writing deterministic code that controls the pins. This system of sub-processors and the pins that they control are known as “Programmable IO.” They are programmed using assembler. There’s much to say about PIO. In the next post that I make on the Pico, I’ll walk you through an introduction to the PIO system.