Hello World

Project Setup

We will start by creating a new Rust library crate:

$ cargo new hello_world --lib
$ cd hello_world


Let's set up our crate by adding ext-php-rs as a dependency and setting the crate type to cdylib. Update the Cargo.toml to look something like so:

name = "hello_world"
version = "0.1.0"
edition = "2018"

crate-type = ["cdylib"]

ext-php-rs = "*"

strip = "debuginfo"


When compiling for Linux and macOS, we do not link directly to PHP, rather PHP will dynamically load the library. We need to tell the linker it's ok to have undefined symbols (as they will be resolved when loaded by PHP).

On Windows, we also need to switch to using the rust-lld linker.

Microsoft Visual C++'s link.exe is supported, however you may run into issues if your linker is not compatible with the linker used to compile PHP.

We do this by creating a Cargo config file in .cargo/config.toml with the following contents:

[target.'cfg(not(target_os = "windows"))']
rustflags = ["-C", "link-arg=-Wl,-undefined,dynamic_lookup"]

linker = "rust-lld"

linker = "rust-lld"

Writing our extension


Let's actually write the extension code now. We start by importing the ext-php-rs prelude, which contains most of the imports required to make a basic extension. We will then write our basic hello_world function, which will take a string argument for the callers name, and we will return another string. Finally, we write a get_module function which is used by PHP to find out about your module. The #[php_module] attribute automatically registers your new function so we don't need to do anything except return the ModuleBuilder that we were given.

We also need to enable the abi_vectorcall feature when compiling for Windows. This is a nightly-only feature so it is recommended to use the #[cfg_attr] macro to not enable the feature on other operating systems.

#![cfg_attr(windows, feature(abi_vectorcall))]
use ext_php_rs::prelude::*;

pub fn hello_world(name: &str) -> String {
    format!("Hello, {}!", name)

pub fn get_module(module: ModuleBuilder) -> ModuleBuilder {

Building the extension

Now let's build our extension. This is done through cargo like any other Rust crate.

If you installed php using a package manager in the previous chapter (or if the php and php-config binaries are already in your $PATH), then you can just run

cargo build

If you have multiple PHP versions in your PATH, or your installation resides in a custom location, you can use the following environment variables:

# explicitly specifies the path to the PHP executable:
export PHP=/path/to/php
# explicitly specifies the path to the php-config executable:
export PHP_CONFIG=/path/to/php-config

As an alternative, if you compiled PHP from source and installed it under it's own prefix (configure --prefix=/my/prefix), you can just put this prefix in front of your PATH:

export PATH="/my/prefix:${PATH}"

Once you've setup these variables, you can just run

cargo build

Cargo will track changes to these environment variables and rebuild the library accordingly.

Testing our extension

The extension we just built is stored inside the cargo target directory: target/debug if you did a debug build, target/release for release builds.

The extension file name is OS-dependent. The naming works as follows:

  • let S be the empty string
  • append to S the value of std::env::consts::DLL_PREFIX (empty on windows, lib on unixes)
  • append to S the lower-snake-case version of your crate name
  • append to S the value of std::env::consts::DLL_SUFFIX (.dll on windows, .dylib on macOS, .so on other unixes).
  • set the filename to the value of S

Which in our case would give us:

  • linux: libhello_world.so
  • macOS: libhello_world.dylib
  • windows: hello_world.dll

Now we need a way to tell the PHP CLI binary to load our extension. There are several ways to do that. For now we'll simply pass the -d extension=/path/to/extension option to the PHP CLI binary.

Let's make a test script:




And run it:

$ php -d extension=./target/debug/libhello_world.so test.php
string(13) "Hello, David!"