freebsd: Try getrandom() first

src/freebsd.rs

@@ -7,9 +7,11 @@
 // except according to those terms.
 
 //! Implementation for FreeBSD
-use crate::util_libc::fill_exact;
+use crate::util_libc::{fill_exact, Weak};
 use crate::Error;
-use core::ptr;
+use core::{mem, ptr};
+
+type GetRandomFn = unsafe extern "C" fn(*mut u8, libc::size_t, libc::c_uint) -> libc::ssize_t;
 
 fn kern_arnd(buf: &mut [u8]) -> libc::ssize_t {
     static MIB: [libc::c_int; 2] = [libc::CTL_KERN, libc::KERN_ARND];
@@ -33,5 +35,11 @@ fn kern_arnd(buf: &mut [u8]) -> libc::ssize_t {
 }
 
 pub fn getrandom_inner(dest: &mut [u8]) -> Result<(), Error> {
-    fill_exact(dest, kern_arnd)
+    static GETRANDOM: Weak = unsafe { Weak::new("getrandom\0") };
+    if let Some(fptr) = GETRANDOM.ptr() {
+        let func: GetRandomFn = unsafe { mem::transmute(fptr) };
+        fill_exact(dest, |buf| unsafe { func(buf.as_mut_ptr(), buf.len(), 0) })
+    } else {
+        fill_exact(dest, kern_arnd)
+    }
 }

src/lib.rs

@@ -16,7 +16,7 @@
 //! | Windows          | [`RtlGenRandom`][3]
 //! | macOS            | [`getentropy()`][19] if available, otherise [`/dev/random`][20] (identical to `/dev/urandom`)
 //! | iOS              | [`SecRandomCopyBytes`][4]
-//! | FreeBSD          | [`kern.arandom`][5]
+//! | FreeBSD          | [`getrandom()`][21] if available, otherise [`kern.arandom`][5]
 //! | OpenBSD          | [`getentropy`][6]
 //! | NetBSD           | [`/dev/urandom`][7] after reading from `/dev/random` once
 //! | Dragonfly BSD    | [`/dev/random`][8]
@@ -101,6 +101,7 @@
 //! [18]: https://software.intel.com/en-us/articles/intel-digital-random-number-generator-drng-software-implementation-guide
 //! [19]: https://www.unix.com/man-page/mojave/2/getentropy/
 //! [20]: https://www.unix.com/man-page/mojave/4/random/
+//! [21]: https://www.freebsd.org/cgi/man.cgi?query=getrandom&manpath=FreeBSD+12.0-stable
 
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