Review fixes

Author: newpavlov

src/lib.rs

@@ -225,17 +225,25 @@ cfg_if! {
         #[path = "use_file.rs"] mod imp;
     } else if #[cfg(all(
         not(feature = "disable_urandom_fallback"),
-        target_os = "linux",
         any(
-            target_arch = "i586",
-            target_arch = "i686",
-            target_arch = "x86",
-            target_arch = "x86_64",
-            target_arch = "arm",
-            target_arch = "armv7",
-            target_arch = "powerpc",
-            target_arch = "powerpc64le",
-            target_arch = "s390x",
+            // Rust supports Android API level 19 (KitKat) [0], while `getrandom(2)`
+            // was added only in level 23 (Marshmallow).
+            // [0]: https://blog.rust-lang.org/2023/01/09/android-ndk-update-r25.html
+            target_os = "android",
+            all(
+                target_os = "linux",
+                // Only on these architectures Rust supports Linux kernel versions (3.2+)
+                // that precede the version (3.17) in which `getrandom(2)` was added:
+                // https://doc.rust-lang.org/stable/rustc/platform-support.html
+                any(
+                    target_arch = "arm",
+                    target_arch = "powerpc",
+                    target_arch = "powerpc64",
+                    target_arch = "s390x",
+                    target_arch = "x86",
+                    target_arch = "x86_64",
+                ),
+            )
         ),
     ))] {
         mod util_libc;

src/linux_android.rs

@@ -1,14 +1,7 @@
-//! Implementation for Linux / Android
-use crate::{util_libc::sys_fill_exact, Error};
+//! Implementation for Linux / Android without `/dev/urandom` fallback
+use crate::{util_libc, Error};
 use core::mem::MaybeUninit;
 
 pub fn getrandom_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
-    sys_fill_exact(dest, |buf| unsafe {
-        libc::syscall(
-            libc::SYS_getrandom,
-            buf.as_mut_ptr() as *mut libc::c_void,
-            buf.len(),
-            0,
-        ) as libc::ssize_t
-    })
+    util_libc::sys_fill_exact(dest, util_libc::getrandom_syscall)
 }

src/linux_with_fallback.rs

@@ -1,7 +1,7 @@
-//! Implementation for Linux / Android
+//! Implementation for Linux with `/dev/urandom` fallback
 use crate::{
     lazy::LazyBool,
-    util_libc::{last_os_error, sys_fill_exact},
+    util_libc::{getrandom_syscall, last_os_error, sys_fill_exact},
     {use_file, Error},
 };
 use core::mem::MaybeUninit;
@@ -10,9 +10,7 @@ pub fn getrandom_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
     // getrandom(2) was introduced in Linux 3.17
     static HAS_GETRANDOM: LazyBool = LazyBool::new();
     if HAS_GETRANDOM.unsync_init(is_getrandom_available) {
-        sys_fill_exact(dest, |buf| unsafe {
-            getrandom(buf.as_mut_ptr() as *mut libc::c_void, buf.len(), 0)
-        })
+        sys_fill_exact(dest, getrandom_syscall)
     } else {
         use_file::getrandom_inner(dest)
     }

src/util_libc.rs

@@ -151,3 +151,16 @@ pub unsafe fn open_readonly(path: &str) -> Result<libc::c_int, Error> {
         }
     }
 }
+
+/// Thin wrapper around the `getrandom()` Linux system call
+#[cfg(any(target_os = "android", target_os = "linux"))]
+pub fn getrandom_syscall(buf: &mut [MaybeUninit<u8>]) -> libc::ssize_t {
+    unsafe {
+        libc::syscall(
+            libc::SYS_getrandom,
+            buf.as_mut_ptr() as *mut libc::c_void,
+            buf.len(),
+            0,
+        ) as libc::ssize_t
+    }
+}