		//! An implementation which calls out to an externally defined function.
		use crate::Error;
		use core::mem::MaybeUninit;

		/// Declares this function as an external implementation of [`fill_uninit`](crate::fill_uninit).
		#[eii(fill_uninit)]
		pub(crate) fn fill_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error>;

		/// Declares this function as an external implementation of [`u32`](crate::u32).
		#[eii(u32)]
		pub(crate) fn inner_u32() -> Result<u32, crate::Error> {
		crate::util::inner_u32()
		}

		/// Declares this function as an external implementation of [`u64`](crate::u64).
		#[eii(u64)]
		pub(crate) fn inner_u64() -> Result<u64, crate::Error> {
		crate::util::inner_u64()
		}

+1

-1

.cargo_vcs_info.json

		{
		"git": {
		"sha1": "b6a28dcbcfc928bc45613f5f6807b93378f2f1be"
		"sha1": "35fd5af2ed77b4a103b5b9a5248f0b8cd56c7aaa"
		},
		"path_in_vcs": ""
		}

+9

-7

benches/buffer.rs

		@@ -0,1 +1,2 @@
		//! Basic benchmarks
		#![feature(test, maybe_uninit_uninit_array_transpose)]
		@@ -26,3 +27,3 @@ extern crate test;
		#[bench]
		pub fn bench_u32(b: &mut test::Bencher) {
		fn bench_u32(b: &mut test::Bencher) {
		#[inline(never)]
		@@ -35,4 +36,5 @@ fn inner() -> u32 {
		}

		#[bench]
		pub fn bench_u32_via_fill(b: &mut test::Bencher) {
		fn bench_u32_via_fill(b: &mut test::Bencher) {
		#[inline(never)]
		@@ -51,3 +53,3 @@ fn inner() -> u32 {
		#[bench]
		pub fn bench_u64(b: &mut test::Bencher) {
		fn bench_u64(b: &mut test::Bencher) {
		#[inline(never)]
		@@ -62,3 +64,3 @@ fn inner() -> u64 {
		#[bench]
		pub fn bench_u64_via_fill(b: &mut test::Bencher) {
		fn bench_u64_via_fill(b: &mut test::Bencher) {
		#[inline(never)]
		@@ -85,5 +87,5 @@ fn inner() -> u64 {
		( $name:ident, $size:expr ) => {
		pub mod $name {
		mod $name {
		#[bench]
		pub fn bench_fill(b: &mut test::Bencher) {
		fn bench_fill(b: &mut test::Bencher) {
		#[inline(never)]
		@@ -98,3 +100,3 @@ fn inner() {
		#[bench]
		pub fn bench_fill_uninit(b: &mut test::Bencher) {
		fn bench_fill_uninit(b: &mut test::Bencher) {
		#[inline(never)]
		@@ -101,0 +103,0 @@ fn inner() {

+2

-0

build.rs

		@@ -0,1 +1,3 @@
		//! Build script for memory sanitization support

		fn main() {
		@@ -2,0 +4,0 @@ // Automatically detect cfg(sanitize = "memory") even if cfg(sanitize) isn't

+106

-61

Cargo.lock

		@@ -48,5 +48,5 @@ # This file is automatically @generated by Cargo.
		name = "cc"
		version = "1.2.53"
		version = "1.2.54"
		source = "registry+https://github.com/rust-lang/crates.io-index"
		checksum = "755d2fce177175ffca841e9a06afdb2c4ab0f593d53b4dee48147dfaade85932"
		checksum = "6354c81bbfd62d9cfa9cb3c773c2b7b2a3a482d569de977fd0e961f6e7c00583"
		dependencies = [
		@@ -82,4 +82,29 @@ "find-msvc-tools",
		[[package]]
		name = "futures-core"
		version = "0.3.31"
		source = "registry+https://github.com/rust-lang/crates.io-index"
		checksum = "05f29059c0c2090612e8d742178b0580d2dc940c837851ad723096f87af6663e"

		[[package]]
		name = "futures-task"
		version = "0.3.31"
		source = "registry+https://github.com/rust-lang/crates.io-index"
		checksum = "f90f7dce0722e95104fcb095585910c0977252f286e354b5e3bd38902cd99988"

		[[package]]
		name = "futures-util"
		version = "0.3.31"
		source = "registry+https://github.com/rust-lang/crates.io-index"
		checksum = "9fa08315bb612088cc391249efdc3bc77536f16c91f6cf495e6fbe85b20a4a81"
		dependencies = [
		"futures-core",
		"futures-task",
		"pin-project-lite",
		"pin-utils",
		"slab",
		]

		[[package]]
		name = "getrandom"
		version = "0.4.0-rc.1"
		version = "0.4.0"
		dependencies = [
		@@ -144,5 +169,5 @@ "cfg-if",
		name = "js-sys"
		version = "0.3.83"
		version = "0.3.85"
		source = "registry+https://github.com/rust-lang/crates.io-index"
		checksum = "464a3709c7f55f1f721e5389aa6ea4e3bc6aba669353300af094b29ffbdde1d8"
		checksum = "8c942ebf8e95485ca0d52d97da7c5a2c387d0e7f0ba4c35e93bfcaee045955b3"
		dependencies = [
		@@ -167,5 +192,5 @@ "once_cell",
		name = "libm"
		version = "0.2.15"
		version = "0.2.16"
		source = "registry+https://github.com/rust-lang/crates.io-index"
		checksum = "f9fbbcab51052fe104eb5e5d351cf728d30a5be1fe14d9be8a3b097481fb97de"
		checksum = "b6d2cec3eae94f9f509c767b45932f1ada8350c4bdb85af2fcab4a3c14807981"

		@@ -226,2 +251,14 @@ [[package]]
		[[package]]
		name = "pin-project-lite"
		version = "0.2.16"
		source = "registry+https://github.com/rust-lang/crates.io-index"
		checksum = "3b3cff922bd51709b605d9ead9aa71031d81447142d828eb4a6eba76fe619f9b"

		[[package]]
		name = "pin-utils"
		version = "0.1.0"
		source = "registry+https://github.com/rust-lang/crates.io-index"
		checksum = "8b870d8c151b6f2fb93e84a13146138f05d02ed11c7e7c54f8826aaaf7c9f184"

		[[package]]
		name = "prettyplease"
		@@ -238,5 +275,5 @@ version = "0.2.37"
		name = "proc-macro2"
		version = "1.0.105"
		version = "1.0.106"
		source = "registry+https://github.com/rust-lang/crates.io-index"
		checksum = "535d180e0ecab6268a3e718bb9fd44db66bbbc256257165fc699dadf70d16fe7"
		checksum = "8fd00f0bb2e90d81d1044c2b32617f68fcb9fa3bb7640c23e9c748e53fb30934"
		dependencies = [
		@@ -248,5 +285,5 @@ "unicode-ident",
		name = "quote"
		version = "1.0.43"
		version = "1.0.44"
		source = "registry+https://github.com/rust-lang/crates.io-index"
		checksum = "dc74d9a594b72ae6656596548f56f667211f8a97b3d4c3d467150794690dc40a"
		checksum = "21b2ebcf727b7760c461f091f9f0f539b77b8e87f2fd88131e7f1b433b3cece4"
		dependencies = [
		@@ -264,5 +301,5 @@ "proc-macro2",
		name = "rand_core"
		version = "0.10.0-rc-6"
		version = "0.10.0"
		source = "registry+https://github.com/rust-lang/crates.io-index"
		checksum = "70765ff7112b0fb2d272d24d9a2f907fc206211304328fe58b2db15a5649ef28"
		checksum = "0c8d0fd677905edcbeedbf2edb6494d676f0e98d54d5cf9bda0b061cb8fb8aba"

		@@ -340,2 +377,8 @@ [[package]]
		[[package]]
		name = "slab"
		version = "0.4.11"
		source = "registry+https://github.com/rust-lang/crates.io-index"
		checksum = "7a2ae44ef20feb57a68b23d846850f861394c2e02dc425a50098ae8c90267589"

		[[package]]
		name = "syn"
		@@ -375,7 +418,7 @@ version = "2.0.114"
		name = "wasip2"
		version = "1.0.1+wasi-0.2.4"
		version = "1.0.2+wasi-0.2.9"
		source = "registry+https://github.com/rust-lang/crates.io-index"
		checksum = "0562428422c63773dad2c345a1882263bbf4d65cf3f42e90921f787ef5ad58e7"
		checksum = "9517f9239f02c069db75e65f174b3da828fe5f5b945c4dd26bd25d89c03ebcf5"
		dependencies = [
		"wit-bindgen 0.46.0",
		"wit-bindgen",
		]
		@@ -385,7 +428,7 @@
		name = "wasip3"
		version = "0.3.1+wasi-0.3.0-rc-2025-09-16"
		version = "0.4.0+wasi-0.3.0-rc-2026-01-06"
		source = "registry+https://github.com/rust-lang/crates.io-index"
		checksum = "87ba4be47b1d11244670d11857eee0758a8f2c39aea64d80b78c1ce29b4642cd"
		checksum = "5428f8bf88ea5ddc08faddef2ac4a67e390b88186c703ce6dbd955e1c145aca5"
		dependencies = [
		"wit-bindgen 0.48.1",
		"wit-bindgen",
		]
		@@ -395,5 +438,5 @@
		name = "wasm-bindgen"
		version = "0.2.106"
		version = "0.2.108"
		source = "registry+https://github.com/rust-lang/crates.io-index"
		checksum = "0d759f433fa64a2d763d1340820e46e111a7a5ab75f993d1852d70b03dbb80fd"
		checksum = "64024a30ec1e37399cf85a7ffefebdb72205ca1c972291c51512360d90bd8566"
		dependencies = [
		@@ -409,7 +452,8 @@ "cfg-if",
		name = "wasm-bindgen-futures"
		version = "0.4.56"
		version = "0.4.58"
		source = "registry+https://github.com/rust-lang/crates.io-index"
		checksum = "836d9622d604feee9e5de25ac10e3ea5f2d65b41eac0d9ce72eb5deae707ce7c"
		checksum = "70a6e77fd0ae8029c9ea0063f87c46fde723e7d887703d74ad2616d792e51e6f"
		dependencies = [
		"cfg-if",
		"futures-util",
		"js-sys",
		@@ -423,5 +467,5 @@ "once_cell",
		name = "wasm-bindgen-macro"
		version = "0.2.106"
		version = "0.2.108"
		source = "registry+https://github.com/rust-lang/crates.io-index"
		checksum = "48cb0d2638f8baedbc542ed444afc0644a29166f1595371af4fecf8ce1e7eeb3"
		checksum = "008b239d9c740232e71bd39e8ef6429d27097518b6b30bdf9086833bd5b6d608"
		dependencies = [
		@@ -434,5 +478,5 @@ "quote",
		name = "wasm-bindgen-macro-support"
		version = "0.2.106"
		version = "0.2.108"
		source = "registry+https://github.com/rust-lang/crates.io-index"
		checksum = "cefb59d5cd5f92d9dcf80e4683949f15ca4b511f4ac0a6e14d4e1ac60c6ecd40"
		checksum = "5256bae2d58f54820e6490f9839c49780dff84c65aeab9e772f15d5f0e913a55"
		dependencies = [
		@@ -448,5 +492,5 @@ "bumpalo",
		name = "wasm-bindgen-shared"
		version = "0.2.106"
		version = "0.2.108"
		source = "registry+https://github.com/rust-lang/crates.io-index"
		checksum = "cbc538057e648b67f72a982e708d485b2efa771e1ac05fec311f9f63e5800db4"
		checksum = "1f01b580c9ac74c8d8f0c0e4afb04eeef2acf145458e52c03845ee9cd23e3d12"
		dependencies = [
		@@ -458,5 +502,5 @@ "unicode-ident",
		name = "wasm-bindgen-test"
		version = "0.3.56"
		version = "0.3.58"
		source = "registry+https://github.com/rust-lang/crates.io-index"
		checksum = "25e90e66d265d3a1efc0e72a54809ab90b9c0c515915c67cdf658689d2c22c6c"
		checksum = "45649196a53b0b7a15101d845d44d2dda7374fc1b5b5e2bbf58b7577ff4b346d"
		dependencies = [
		@@ -476,2 +520,3 @@ "async-trait",
		"wasm-bindgen-test-macro",
		"wasm-bindgen-test-shared",
		]
		@@ -481,5 +526,5 @@
		name = "wasm-bindgen-test-macro"
		version = "0.3.56"
		version = "0.3.58"
		source = "registry+https://github.com/rust-lang/crates.io-index"
		checksum = "7150335716dce6028bead2b848e72f47b45e7b9422f64cccdc23bedca89affc1"
		checksum = "f579cdd0123ac74b94e1a4a72bd963cf30ebac343f2df347da0b8df24cdebed2"
		dependencies = [
		@@ -492,6 +537,12 @@ "proc-macro2",
		[[package]]
		name = "wasm-bindgen-test-shared"
		version = "0.2.108"
		source = "registry+https://github.com/rust-lang/crates.io-index"
		checksum = "a8145dd1593bf0fb137dbfa85b8be79ec560a447298955877804640e40c2d6ea"

		[[package]]
		name = "wasm-encoder"
		version = "0.241.2"
		version = "0.244.0"
		source = "registry+https://github.com/rust-lang/crates.io-index"
		checksum = "e01164c9dda68301e34fdae536c23ed6fe90ce6d97213ccc171eebbd3d02d6b8"
		checksum = "990065f2fe63003fe337b932cfb5e3b80e0b4d0f5ff650e6985b1048f62c8319"
		dependencies = [
		@@ -504,5 +555,5 @@ "leb128fmt",
		name = "wasm-metadata"
		version = "0.241.2"
		version = "0.244.0"
		source = "registry+https://github.com/rust-lang/crates.io-index"
		checksum = "876fe286f2fa416386deedebe8407e6f19e0b5aeaef3d03161e77a15fa80f167"
		checksum = "bb0e353e6a2fbdc176932bbaab493762eb1255a7900fe0fea1a2f96c296cc909"
		dependencies = [
		@@ -517,5 +568,5 @@ "anyhow",
		name = "wasmparser"
		version = "0.241.2"
		version = "0.244.0"
		source = "registry+https://github.com/rust-lang/crates.io-index"
		checksum = "46d90019b1afd4b808c263e428de644f3003691f243387d30d673211ee0cb8e8"
		checksum = "47b807c72e1bac69382b3a6fb3dbe8ea4c0ed87ff5629b8685ae6b9a611028fe"
		dependencies = [
		@@ -530,5 +581,5 @@ "bitflags",
		name = "web-sys"
		version = "0.3.83"
		version = "0.3.85"
		source = "registry+https://github.com/rust-lang/crates.io-index"
		checksum = "9b32828d774c412041098d182a8b38b16ea816958e07cf40eec2bc080ae137ac"
		checksum = "312e32e551d92129218ea9a2452120f4aabc03529ef03e4d0d82fb2780608598"
		dependencies = [
		@@ -565,11 +616,5 @@ "js-sys",
		name = "wit-bindgen"
		version = "0.46.0"
		version = "0.51.0"
		source = "registry+https://github.com/rust-lang/crates.io-index"
		checksum = "f17a85883d4e6d00e8a97c586de764dabcc06133f7f1d55dce5cdc070ad7fe59"

		[[package]]
		name = "wit-bindgen"
		version = "0.48.1"
		source = "registry+https://github.com/rust-lang/crates.io-index"
		checksum = "7f8c2adb5f74ac9395bc3121c99a1254bf9310482c27b13f97167aedb5887138"
		checksum = "d7249219f66ced02969388cf2bb044a09756a083d0fab1e566056b04d9fbcaa5"
		dependencies = [
		@@ -581,5 +626,5 @@ "wit-bindgen-rust-macro",
		name = "wit-bindgen-core"
		version = "0.48.1"
		version = "0.51.0"
		source = "registry+https://github.com/rust-lang/crates.io-index"
		checksum = "9b881a098cae03686d7a0587f8f306f8a58102ad8da8b5599100fbe0e7f5800b"
		checksum = "ea61de684c3ea68cb082b7a88508a8b27fcc8b797d738bfc99a82facf1d752dc"
		dependencies = [
		@@ -593,5 +638,5 @@ "anyhow",
		name = "wit-bindgen-rust"
		version = "0.48.1"
		version = "0.51.0"
		source = "registry+https://github.com/rust-lang/crates.io-index"
		checksum = "69667efa439a453e1d50dac939c6cab6d2c3ac724a9d232b6631dad2472a5b70"
		checksum = "b7c566e0f4b284dd6561c786d9cb0142da491f46a9fbed79ea69cdad5db17f21"
		dependencies = [
		@@ -610,5 +655,5 @@ "anyhow",
		name = "wit-bindgen-rust-macro"
		version = "0.48.1"
		version = "0.51.0"
		source = "registry+https://github.com/rust-lang/crates.io-index"
		checksum = "eae2e22cceb5d105d52326c07e3e67603a861cc7add70fc467f7cc7ec5265017"
		checksum = "0c0f9bfd77e6a48eccf51359e3ae77140a7f50b1e2ebfe62422d8afdaffab17a"
		dependencies = [
		@@ -626,5 +671,5 @@ "anyhow",
		name = "wit-component"
		version = "0.241.2"
		version = "0.244.0"
		source = "registry+https://github.com/rust-lang/crates.io-index"
		checksum = "1fd0c57df25e7ee612d946d3b7646c1ddb2310f8280aa2c17e543b66e0812241"
		checksum = "9d66ea20e9553b30172b5e831994e35fbde2d165325bec84fc43dbf6f4eb9cb2"
		dependencies = [
		@@ -646,5 +691,5 @@ "anyhow",
		name = "wit-parser"
		version = "0.241.2"
		version = "0.244.0"
		source = "registry+https://github.com/rust-lang/crates.io-index"
		checksum = "09ef1c6ad67f35c831abd4039c02894de97034100899614d1c44e2268ad01c91"
		checksum = "ecc8ac4bc1dc3381b7f59c34f00b67e18f910c2c0f50015669dde7def656a736"
		dependencies = [
		@@ -665,4 +710,4 @@ "anyhow",
		name = "zmij"
		version = "1.0.15"
		version = "1.0.17"
		source = "registry+https://github.com/rust-lang/crates.io-index"
		checksum = "94f63c051f4fe3c1509da62131a678643c5b6fbdc9273b2b79d4378ebda003d2"
		checksum = "02aae0f83f69aafc94776e879363e9771d7ecbffe2c7fbb6c14c5e00dfe88439"

+25

-5

Cargo.toml

		@@ -16,3 +16,3 @@ # THIS FILE IS AUTOMATICALLY GENERATED BY CARGO
		name = "getrandom"
		version = "0.4.0-rc.1"
		version = "0.4.0"
		authors = ["The Rand Project Developers"]
		@@ -41,2 +41,3 @@ build = "build.rs"
		]
		rustdoc-args = ['--cfg getrandom_backend="extern_impl"']

		@@ -81,3 +82,3 @@ [package.metadata.cross.target.x86_64-unknown-netbsd]
		[dependencies.rand_core]
		version = "0.10.0-rc-6"
		version = "0.10.0"
		optional = true
		@@ -107,4 +108,3 @@
		[target.'cfg(all(target_arch = "wasm32", target_os = "wasi", target_env = "p3"))'.dependencies.wasip3]
		version = "0.3"
		default-features = false
		version = "0.4"

		@@ -143,2 +143,21 @@ [target.'cfg(all(target_os = "uefi", getrandom_backend = "efi_rng"))'.dependencies.r-efi]

		[lints.clippy]
		cast_lossless = "warn"
		cast_possible_truncation = "warn"
		cast_possible_wrap = "warn"
		cast_precision_loss = "warn"
		cast_ptr_alignment = "warn"
		cast_sign_loss = "warn"
		char_lit_as_u8 = "warn"
		checked_conversions = "warn"
		fn_to_numeric_cast = "warn"
		fn_to_numeric_cast_with_truncation = "warn"
		ptr_as_ptr = "warn"
		unnecessary_cast = "warn"
		useless_conversion = "warn"

		[lints.rust]
		missing_docs = "warn"
		unused_lifetimes = "warn"

		[lints.rust.unexpected_cfgs]
		@@ -148,3 +167,3 @@ level = "warn"
		check-cfg = [
		'cfg(getrandom_backend, values("custom", "efi_rng", "rdrand", "rndr", "linux_getrandom", "linux_raw", "windows_legacy", "unsupported"))',
		'cfg(getrandom_backend, values("custom", "efi_rng", "rdrand", "rndr", "linux_getrandom", "linux_raw", "windows_legacy", "unsupported", "extern_impl"))',
		"cfg(getrandom_msan)",
		@@ -155,2 +174,3 @@ "cfg(getrandom_test_linux_fallback)",
		'cfg(target_os, values("cygwin"))',
		'cfg(target_os, values("motor"))',
		]

+5

-1

CHANGELOG.md

		@@ -7,3 +7,3 @@ # Changelog

		## [Unreleased]
		## [0.4.0] - 2026-02-02

		@@ -14,2 +14,4 @@ ### Added
		- WASIp3 support [#779]
		- `extern_impl` opt-in backend [#786] [#794]
		- Motor OS support [#797]

		@@ -23,2 +25,4 @@ ### Changed
		[#779]: https://github.com/rust-random/getrandom/pull/779
		[#786]: https://github.com/rust-random/getrandom/pull/786
		[#794]: https://github.com/rust-random/getrandom/pull/794

		@@ -25,0 +29,0 @@ ## [0.3.4] - 2025-10-14

+46

-11

README.md

		@@ -46,3 +46,3 @@ # getrandom: system's random number generator
		\| Linux, Android \| `‑linux‑` \| [`getrandom`][1] system call if available, otherwise [`/dev/urandom`][2] after successfully polling `/dev/random`
		\| Windows 10+ \| `‑windows‑` \| [`ProcessPrng`] on Rust 1.78+, [`RtlGenRandom`] otherwise
		\| Windows 10+ \| `‑windows‑` \| [`ProcessPrng`]
		\| Windows 7, 8 \| `-win7‑windows‑` \| [`RtlGenRandom`]
		@@ -74,2 +74,3 @@ \| macOS \| `*‑apple‑darwin` \| [`getentropy`][3]
		\| Cygwin \| `*-cygwin` \| [`getrandom`][20] (based on [`RtlGenRandom`])
		\| Motor OS \| `x86_64-unknown-motor` \| [`RDRAND`]

		@@ -104,12 +105,13 @@ Pull Requests that add support for new targets to `getrandom` are always welcome.

		\| Backend name \| Target \| Target Triple \| Implementation
		\| ----------------- \| -------------------- \| ------------------------ \| --------------
		\| `linux_getrandom` \| Linux, Android \| `‑linux‑` \| [`getrandom`][1] system call (without `/dev/urandom` fallback). Bumps minimum supported Linux kernel version to 3.17 and Android API level to 23 (Marshmallow).
		\| `linux_raw` \| Linux, Android \| `‑linux‑` \| Same as `linux_getrandom`, but uses raw `asm!`-based syscalls instead of `libc`.
		\| `rdrand` \| x86, x86-64 \| `x86_64-`, `i686-` \| [`RDRAND`] instruction
		\| `rndr` \| AArch64 \| `aarch64-*` \| [`RNDR`] register
		\| `efi_rng` \| UEFI \| `*-unknown‑uefi` \| [`EFI_RNG_PROTOCOL`] with `EFI_RNG_ALGORITHM_RAW` (requires `std` and Nightly compiler)
		\| `windows_legacy` \| Windows \| `-windows-` \| [`RtlGenRandom`]
		\| `custom` \| All targets \| `*` \| User-provided custom implementation (see [custom backend])
		\| `unsupported` \| All targets \| `*` \| Always returns `Err(Error::UNSUPPORTED)` (see [unsupported backend])
		\| Backend name \| Target \| Target Triple \| Implementation
		\| ------------------- \| -------------------- \| ------------------------ \| --------------
		\| `linux_getrandom` \| Linux, Android \| `‑linux‑` \| [`getrandom`][1] system call (without `/dev/urandom` fallback). Bumps minimum supported Linux kernel version to 3.17 and Android API level to 23 (Marshmallow).
		\| `linux_raw` \| Linux, Android \| `‑linux‑` \| Same as `linux_getrandom`, but uses raw `asm!`-based syscalls instead of `libc`.
		\| `rdrand` \| x86, x86-64 \| `x86_64-`, `i686-` \| [`RDRAND`] instruction
		\| `rndr` \| AArch64 \| `aarch64-*` \| [`RNDR`] register
		\| `efi_rng` \| UEFI \| `*-unknown‑uefi` \| [`EFI_RNG_PROTOCOL`] with `EFI_RNG_ALGORITHM_RAW` (requires `std` and Nightly compiler)
		\| `windows_legacy` \| Windows \| `-windows-` \| [`RtlGenRandom`]
		\| `custom` \| All targets \| `*` \| User-provided custom implementation (see [custom backend])
		\| `unsupported` \| All targets \| `*` \| Always returns `Err(Error::UNSUPPORTED)` (see [unsupported backend])
		\| `extern_impl` \| All targets \| `*` \| Externally-provided custom implementation (see [externally implemented interface])

		@@ -207,2 +209,34 @@ Opt-in backends can be enabled using the `getrandom_backend` configuration flag.

		### Externally Implemented Interface

		Using the nightly-only feature [`extern_item_impls`] it is possible to provide
		a custom backend for `getrandom`, even to override an existing first-party implementation.
		First, enable the `extern_impl` opt-in backend to allow usage of this nightly feature.
		Then, you may provide implementations for `fill_uninit`, `u32`, and/or `u64`
		with an attribute macro from the `implementation` module.

		[`extern_item_impls`]: https://github.com/rust-lang/rust/issues/125418

		```rust
		use core::mem::MaybeUninit;

		#[cfg(getrandom_backend = "extern_impl")]
		#[getrandom::implementation::fill_uninit]
		fn my_fill_uninit_implementation(
		dest: &mut [MaybeUninit<u8>]
		) -> Result<(), getrandom::Error> {
		// ...
		Ok(())
		}
		```

		For further details on what a suitable implementation for `fill_uninit` may look
		like, see [custom backend].

		`getrandom` will provide a default implementation for `u32` and `u64`, but does
		not currently provide a default for `fill_uninit`, even if one is normally
		available for the current target. If no implementation is available,
		a compilation error will be raised with instructions for how to provide
		an implementation.

		### Unsupported backend
		@@ -380,2 +414,3 @@
		[opt-in]: #opt-in-backends
		[externally implemented interface]: #externally-implemented-interface

		@@ -382,0 +417,0 @@ [//]: # (licenses)

+6

-0

src/backends.rs

		@@ -35,2 +35,5 @@ //! System-specific implementations.
		pub use unsupported::*;
		} else if #[cfg(getrandom_backend = "extern_impl")] {
		pub(crate) mod extern_impl;
		pub use extern_impl::*;
		} else if #[cfg(all(target_os = "linux", target_env = ""))] {
		@@ -150,2 +153,5 @@ mod linux_raw;
		pub use hermit::*;
		} else if #[cfg(all(target_arch = "x86_64", target_os = "motor"))] {
		mod rdrand;
		pub use rdrand::*;
		} else if #[cfg(target_os = "vxworks")] {
		@@ -152,0 +158,0 @@ mod vxworks;

+28

-16

src/lib.rs

		@@ -11,20 +11,5 @@ // Overwrite links to crate items with intra-crate links
		#![doc = include_str!("../README.md")]
		#![warn(rust_2018_idioms, unused_lifetimes, missing_docs)]
		#![cfg_attr(docsrs, feature(doc_cfg))]
		#![cfg_attr(getrandom_backend = "efi_rng", feature(uefi_std))]
		#![deny(
		clippy::cast_lossless,
		clippy::cast_possible_truncation,
		clippy::cast_possible_wrap,
		clippy::cast_precision_loss,
		clippy::cast_ptr_alignment,
		clippy::cast_sign_loss,
		clippy::char_lit_as_u8,
		clippy::checked_conversions,
		clippy::fn_to_numeric_cast,
		clippy::fn_to_numeric_cast_with_truncation,
		clippy::ptr_as_ptr,
		clippy::unnecessary_cast,
		clippy::useless_conversion
		)]
		#![cfg_attr(getrandom_backend = "extern_impl", feature(extern_item_impls))]

		@@ -54,2 +39,29 @@ #[macro_use]

		/// Attribute macros for overwriting the core functionality of this crate.
		///
		/// This allows `getrandom` to provide a default implementation and a common interface
		/// for all crates to use, while giving users a safe way to override that default where required.
		///
		/// Must be enabled via the `extern_impl` opt-in backend, as this functionality
		/// is currently limited to nightly.
		///
		/// # Examples
		///
		/// ```rust
		/// # use core::mem::MaybeUninit;
		/// # #[cfg(getrandom_backend = "extern_impl")]
		/// #[getrandom::implementation::fill_uninit]
		/// fn my_fill_uninit_implementation(
		/// dest: &mut [MaybeUninit<u8>]
		/// ) -> Result<(), getrandom::Error> {
		/// // ...
		/// # let _ = dest;
		/// # Err(Error::UNSUPPORTED)
		/// }
		/// ```
		#[cfg(getrandom_backend = "extern_impl")]
		pub mod implementation {
		pub use crate::backends::extern_impl::{fill_uninit, u32, u64};
		}

		/// Fill `dest` with random bytes from the system's preferred random number source.
		@@ -56,0 +68,0 @@ ///

+1

-0

src/sys_rng.rs

		@@ -32,2 +32,3 @@ use crate::Error;
		/// [`Rng`]: rand_core::Rng
		/// [`UnwrapErr`]: rand_core::UnwrapErr
		#[derive(Clone, Copy, Debug, Default)]
		@@ -34,0 +35,0 @@ pub struct SysRng;

+1

-84

tests/mod.rs

		@@ -0,1 +1,2 @@
		//! Main `getrandom` tests
		use core::mem::MaybeUninit;
		@@ -209,85 +210,1 @@ use getrandom::{fill, fill_uninit};
		}

		#[cfg(getrandom_backend = "custom")]
		mod custom {
		use getrandom::Error;

		struct Xoshiro128PlusPlus {
		s: [u32; 4],
		}

		impl Xoshiro128PlusPlus {
		fn new(mut seed: u64) -> Self {
		const PHI: u64 = 0x9e3779b97f4a7c15;
		let mut s = [0u32; 4];
		for val in s.iter_mut() {
		seed = seed.wrapping_add(PHI);
		let mut z = seed;
		z = (z ^ (z >> 30)).wrapping_mul(0xbf58476d1ce4e5b9);
		z = (z ^ (z >> 27)).wrapping_mul(0x94d049bb133111eb);
		z = z ^ (z >> 31);
		*val = z as u32;
		}
		Self { s }
		}

		fn next_u32(&mut self) -> u32 {
		let res = self.s[0]
		.wrapping_add(self.s[3])
		.rotate_left(7)
		.wrapping_add(self.s[0]);

		let t = self.s[1] << 9;

		self.s[2] ^= self.s[0];
		self.s[3] ^= self.s[1];
		self.s[1] ^= self.s[2];
		self.s[0] ^= self.s[3];

		self.s[2] ^= t;

		self.s[3] = self.s[3].rotate_left(11);

		res
		}
		}

		// This implementation uses current timestamp as a PRNG seed.
		//
		// WARNING: this custom implementation is for testing purposes ONLY!

		#[unsafe(no_mangle)]
		unsafe extern "Rust" fn __getrandom_v03_custom(dest: *mut u8, len: usize) -> Result<(), Error> {
		use std::time::{SystemTime, UNIX_EPOCH};

		assert_ne!(len, 0);

		if len == 142 {
		return Err(Error::new_custom(142));
		}

		let dest_u32 = dest.cast::<u32>();
		let ts = SystemTime::now().duration_since(UNIX_EPOCH).unwrap();
		let mut rng = Xoshiro128PlusPlus::new(ts.as_nanos() as u64);
		for i in 0..len / 4 {
		let val = rng.next_u32();
		unsafe { core::ptr::write_unaligned(dest_u32.add(i), val) };
		}
		if len % 4 != 0 {
		let start = 4 * (len / 4);
		for i in start..len {
		let val = rng.next_u32();
		unsafe { core::ptr::write_unaligned(dest.add(i), val as u8) };
		}
		}
		Ok(())
		}

		// Test that enabling the custom feature indeed uses the custom implementation
		#[test]
		fn test_custom() {
		let mut buf = [0u8; 142];
		let res = getrandom::fill(&mut buf);
		assert!(res.is_err());
		}
		}

+1

-0

tests/sys_rng.rs

		@@ -0,1 +1,2 @@
		//! Tests for `SysRng`
		#![cfg(feature = "sys_rng")]
		@@ -2,0 +3,0 @@

Cargo.toml.orig

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LICENSE-MIT

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