Solaris: consistantly use /dev/random source

On Solaris, we opt to use /dev/random source instead of /dev/urandom due
to reasons explained in the comments and
[in this Solaris blog post](https://blogs.oracle.com/solaris/post/solaris-new-system-calls-getentropy2-and-getrandom2).

However, we haven't been making the same choice when getting randomness
via the `getrandom(2)` function, as we just pass `0` for the flags. We
[used to](https://github.com/rust-random/rand/pull/730/files#diff-694d4302a3ff2a976f2fbd34bc05ada22ee61a4e21d2d985beab27f7a809268fR151)
always set `GRND_RANDOM`, but that was removed in the move from `OsRng`
to this crate.

For context, rust-random/rand#730,
#9, and
#51 are the major changes
to the Solaris/Illumos implementation over the years.

See the solaris documentation for:
- [`getrandom(2)`](https://docs.oracle.com/cd/E88353_01/html/E37841/getrandom-2.html)
- [`urandom(4)`](https://docs.oracle.com/cd/E88353_01/html/E37851/urandom-4d.html)

I also updated the doucmentation to better reflect when
[Illumos added the `getrandom(2)` function](https://www.illumos.org/issues/9971#change-23483).

Signed-off-by: Joe Richey <joerichey@google.com>

Cargo.toml

@@ -18,7 +18,7 @@ compiler_builtins = { version = "0.1", optional = true }
 core = { version = "1.0", optional = true, package = "rustc-std-workspace-core" }
 
 [target.'cfg(unix)'.dependencies]
-libc = { version = "0.2.120", default-features = false }
+libc = { version = "0.2.128", default-features = false }
 
 [target.'cfg(target_os = "wasi")'.dependencies]
 wasi = "0.11"

src/solaris_illumos.rs

@@ -8,12 +8,11 @@
 
 //! Implementation for the Solaris family
 //!
-//! Read from `/dev/random`, with chunks of limited size (256 bytes).
 //! `/dev/random` uses the Hash_DRBG with SHA512 algorithm from NIST SP 800-90A.
 //! `/dev/urandom` uses the FIPS 186-2 algorithm, which is considered less
-//! secure. We choose to read from `/dev/random`.
+//! secure. We choose to read from `/dev/random` (and use GRND_RANDOM).
 //!
-//! Since Solaris 11.3 and mid-2015 illumos, the `getrandom` syscall is available.
+//! Solaris 11.3 and late-2018 illumos added the getrandom(2) libc function.
 //! To make sure we can compile on both Solaris and its derivatives, as well as
 //! function, we check for the existence of getrandom(2) in libc by calling
 //! libc::dlsym.
@@ -24,21 +23,23 @@ use crate::{
 };
 use core::mem::{self, MaybeUninit};
 
-#[cfg(target_os = "illumos")]
-type GetRandomFn = unsafe extern "C" fn(*mut u8, libc::size_t, libc::c_uint) -> libc::ssize_t;
-#[cfg(target_os = "solaris")]
-type GetRandomFn = unsafe extern "C" fn(*mut u8, libc::size_t, libc::c_uint) -> libc::c_int;
+static GETRANDOM: Weak = unsafe { Weak::new("getrandom\0") };
+type GetRandomFn =
+    unsafe extern "C" fn(*mut libc::c_void, libc::size_t, libc::c_uint) -> libc::ssize_t;
 
 pub fn getrandom_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
-    // getrandom(2) was introduced in Solaris 11.3 for Illumos in 2015.
-    static GETRANDOM: Weak = unsafe { Weak::new("getrandom\0") };
     if let Some(fptr) = GETRANDOM.ptr() {
         let func: GetRandomFn = unsafe { mem::transmute(fptr) };
         // 256 bytes is the lowest common denominator across all the Solaris
         // derived platforms for atomically obtaining random data.
         for chunk in dest.chunks_mut(256) {
             sys_fill_exact(chunk, |buf| unsafe {
-                func(buf.as_mut_ptr() as *mut u8, buf.len(), 0) as libc::ssize_t
+                // A cast is needed for the flags as libc uses the wrong type.
+                func(
+                    buf.as_mut_ptr() as *mut libc::c_void,
+                    buf.len(),
+                    libc::GRND_RANDOM as libc::c_uint,
+                )
             })?
         }
         Ok(())