diff --git a/library/std/src/os/fortanix_sgx/ffi.rs b/library/std/src/os/fortanix_sgx/ffi.rs
index 63fc5ff2866a8..ac1db0e5e39cc 100644
--- a/library/std/src/os/fortanix_sgx/ffi.rs
+++ b/library/std/src/os/fortanix_sgx/ffi.rs
@@ -34,5 +34,8 @@
 
 #![unstable(feature = "sgx_platform", issue = "56975")]
 
+#[path = "../unix/ffi/os_str.rs"]
+mod os_str;
+
 #[unstable(feature = "sgx_platform", issue = "56975")]
-pub use crate::sys_common::os_str_bytes::*;
+pub use self::os_str::{OsStrExt, OsStringExt};
diff --git a/library/std/src/os/hermit/ffi.rs b/library/std/src/os/hermit/ffi.rs
index 07b59a02556d9..19761fd99b400 100644
--- a/library/std/src/os/hermit/ffi.rs
+++ b/library/std/src/os/hermit/ffi.rs
@@ -34,5 +34,8 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
+#[path = "../unix/ffi/os_str.rs"]
+mod os_str;
+
 #[stable(feature = "rust1", since = "1.0.0")]
-pub use crate::sys_common::os_str_bytes::*;
+pub use self::os_str::{OsStrExt, OsStringExt};
diff --git a/library/std/src/os/unix/ffi.rs b/library/std/src/os/unix/ffi/mod.rs
similarity index 93%
rename from library/std/src/os/unix/ffi.rs
rename to library/std/src/os/unix/ffi/mod.rs
index 123f85deaf9e3..c29df6596fd94 100644
--- a/library/std/src/os/unix/ffi.rs
+++ b/library/std/src/os/unix/ffi/mod.rs
@@ -34,5 +34,7 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
+mod os_str;
+
 #[stable(feature = "rust1", since = "1.0.0")]
-pub use crate::sys_common::os_str_bytes::*;
+pub use self::os_str::{OsStrExt, OsStringExt};
diff --git a/library/std/src/os/unix/ffi/os_str.rs b/library/std/src/os/unix/ffi/os_str.rs
new file mode 100644
index 0000000000000..54c9a9382f22f
--- /dev/null
+++ b/library/std/src/os/unix/ffi/os_str.rs
@@ -0,0 +1,68 @@
+use crate::ffi::{OsStr, OsString};
+use crate::mem;
+use crate::sealed::Sealed;
+use crate::sys::os_str::Buf;
+use crate::sys_common::{AsInner, FromInner, IntoInner};
+
+// Note: this file is currently reused in other `std::os::{platform}::ffi` modules to reduce duplication.
+// Keep this in mind when applying changes to this file that only apply to `unix`.
+
+/// Platform-specific extensions to [`OsString`].
+///
+/// This trait is sealed: it cannot be implemented outside the standard library.
+/// This is so that future additional methods are not breaking changes.
+#[stable(feature = "rust1", since = "1.0.0")]
+pub trait OsStringExt: Sealed {
+    /// Creates an [`OsString`] from a byte vector.
+    ///
+    /// See the module documentation for an example.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn from_vec(vec: Vec<u8>) -> Self;
+
+    /// Yields the underlying byte vector of this [`OsString`].
+    ///
+    /// See the module documentation for an example.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn into_vec(self) -> Vec<u8>;
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl OsStringExt for OsString {
+    fn from_vec(vec: Vec<u8>) -> OsString {
+        FromInner::from_inner(Buf { inner: vec })
+    }
+    fn into_vec(self) -> Vec<u8> {
+        self.into_inner().inner
+    }
+}
+
+/// Platform-specific extensions to [`OsStr`].
+///
+/// This trait is sealed: it cannot be implemented outside the standard library.
+/// This is so that future additional methods are not breaking changes.
+#[stable(feature = "rust1", since = "1.0.0")]
+pub trait OsStrExt: Sealed {
+    #[stable(feature = "rust1", since = "1.0.0")]
+    /// Creates an [`OsStr`] from a byte slice.
+    ///
+    /// See the module documentation for an example.
+    fn from_bytes(slice: &[u8]) -> &Self;
+
+    /// Gets the underlying byte view of the [`OsStr`] slice.
+    ///
+    /// See the module documentation for an example.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn as_bytes(&self) -> &[u8];
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl OsStrExt for OsStr {
+    #[inline]
+    fn from_bytes(slice: &[u8]) -> &OsStr {
+        unsafe { mem::transmute(slice) }
+    }
+    #[inline]
+    fn as_bytes(&self) -> &[u8] {
+        &self.as_inner().inner
+    }
+}
diff --git a/library/std/src/os/wasi/ffi.rs b/library/std/src/os/wasi/ffi.rs
index f71f316d1ba10..17e12a395a670 100644
--- a/library/std/src/os/wasi/ffi.rs
+++ b/library/std/src/os/wasi/ffi.rs
@@ -2,5 +2,8 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
+#[path = "../unix/ffi/os_str.rs"]
+mod os_str;
+
 #[stable(feature = "rust1", since = "1.0.0")]
-pub use crate::sys_common::os_str_bytes::*;
+pub use self::os_str::{OsStrExt, OsStringExt};
diff --git a/library/std/src/sys/hermit/args.rs b/library/std/src/sys/hermit/args.rs
index 4eb0d8437ba5f..1c7e1dd8d5778 100644
--- a/library/std/src/sys/hermit/args.rs
+++ b/library/std/src/sys/hermit/args.rs
@@ -55,8 +55,8 @@ impl DoubleEndedIterator for Args {
 mod imp {
     use super::Args;
     use crate::ffi::{CStr, OsString};
+    use crate::os::unix::ffi::OsStringExt;
     use crate::ptr;
-    use crate::sys_common::os_str_bytes::*;
 
     use crate::sys_common::mutex::StaticMutex;
 
diff --git a/library/std/src/sys/hermit/fs.rs b/library/std/src/sys/hermit/fs.rs
index 76ea70d997f5d..be019d4435db5 100644
--- a/library/std/src/sys/hermit/fs.rs
+++ b/library/std/src/sys/hermit/fs.rs
@@ -3,6 +3,7 @@ use crate::fmt;
 use crate::hash::{Hash, Hasher};
 use crate::io::{self, Error, ErrorKind};
 use crate::io::{IoSlice, IoSliceMut, SeekFrom};
+use crate::os::unix::ffi::OsStrExt;
 use crate::path::{Path, PathBuf};
 use crate::sys::cvt;
 use crate::sys::hermit::abi;
@@ -10,7 +11,6 @@ use crate::sys::hermit::abi::{O_APPEND, O_CREAT, O_EXCL, O_RDONLY, O_RDWR, O_TRU
 use crate::sys::hermit::fd::FileDesc;
 use crate::sys::time::SystemTime;
 use crate::sys::unsupported;
-use crate::sys_common::os_str_bytes::OsStrExt;
 
 pub use crate::sys_common::fs::{copy, try_exists};
 //pub use crate::sys_common::fs::remove_dir_all;
diff --git a/library/std/src/sys/hermit/os.rs b/library/std/src/sys/hermit/os.rs
index 40bd393098f57..eeb30a578c05b 100644
--- a/library/std/src/sys/hermit/os.rs
+++ b/library/std/src/sys/hermit/os.rs
@@ -4,13 +4,13 @@ use crate::ffi::{CStr, OsStr, OsString};
 use crate::fmt;
 use crate::io;
 use crate::marker::PhantomData;
+use crate::os::unix::ffi::OsStringExt;
 use crate::path::{self, PathBuf};
 use crate::str;
 use crate::sync::Mutex;
 use crate::sys::hermit::abi;
 use crate::sys::memchr;
 use crate::sys::unsupported;
-use crate::sys_common::os_str_bytes::*;
 use crate::vec;
 
 pub fn errno() -> i32 {
diff --git a/library/std/src/sys_common/os_str_bytes.rs b/library/std/src/sys_common/os_str_bytes.rs
index 32705c432fa8a..470f401a6d254 100644
--- a/library/std/src/sys_common/os_str_bytes.rs
+++ b/library/std/src/sys_common/os_str_bytes.rs
@@ -2,30 +2,25 @@
 //! systems: just a `Vec<u8>`/`[u8]`.
 
 use crate::borrow::Cow;
-use crate::ffi::{OsStr, OsString};
+
 use crate::fmt;
 use crate::mem;
 use crate::rc::Rc;
-use crate::sealed::Sealed;
 use crate::str;
 use crate::sync::Arc;
 use crate::sys_common::bytestring::debug_fmt_bytestring;
-use crate::sys_common::{AsInner, FromInner, IntoInner};
+use crate::sys_common::{AsInner, IntoInner};
 
 use core::str::lossy::Utf8Lossy;
 
 #[derive(Hash)]
-pub(crate) struct Buf {
+#[repr(transparent)]
+pub struct Buf {
     pub inner: Vec<u8>,
 }
 
-// FIXME:
-// `Buf::as_slice` current implementation relies
-// on `Slice` being layout-compatible with `[u8]`.
-// When attribute privacy is implemented, `Slice` should be annotated as `#[repr(transparent)]`.
-// Anyway, `Slice` representation and layout are considered implementation detail, are
-// not documented and must not be relied upon.
-pub(crate) struct Slice {
+#[repr(transparent)]
+pub struct Slice {
     pub inner: [u8],
 }
 
@@ -243,63 +238,3 @@ impl Slice {
         self.inner.eq_ignore_ascii_case(&other.inner)
     }
 }
-
-/// Platform-specific extensions to [`OsString`].
-///
-/// This trait is sealed: it cannot be implemented outside the standard library.
-/// This is so that future additional methods are not breaking changes.
-#[stable(feature = "rust1", since = "1.0.0")]
-pub trait OsStringExt: Sealed {
-    /// Creates an [`OsString`] from a byte vector.
-    ///
-    /// See the module documentation for an example.
-    #[stable(feature = "rust1", since = "1.0.0")]
-    fn from_vec(vec: Vec<u8>) -> Self;
-
-    /// Yields the underlying byte vector of this [`OsString`].
-    ///
-    /// See the module documentation for an example.
-    #[stable(feature = "rust1", since = "1.0.0")]
-    fn into_vec(self) -> Vec<u8>;
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl OsStringExt for OsString {
-    fn from_vec(vec: Vec<u8>) -> OsString {
-        FromInner::from_inner(Buf { inner: vec })
-    }
-    fn into_vec(self) -> Vec<u8> {
-        self.into_inner().inner
-    }
-}
-
-/// Platform-specific extensions to [`OsStr`].
-///
-/// This trait is sealed: it cannot be implemented outside the standard library.
-/// This is so that future additional methods are not breaking changes.
-#[stable(feature = "rust1", since = "1.0.0")]
-pub trait OsStrExt: Sealed {
-    #[stable(feature = "rust1", since = "1.0.0")]
-    /// Creates an [`OsStr`] from a byte slice.
-    ///
-    /// See the module documentation for an example.
-    fn from_bytes(slice: &[u8]) -> &Self;
-
-    /// Gets the underlying byte view of the [`OsStr`] slice.
-    ///
-    /// See the module documentation for an example.
-    #[stable(feature = "rust1", since = "1.0.0")]
-    fn as_bytes(&self) -> &[u8];
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl OsStrExt for OsStr {
-    #[inline]
-    fn from_bytes(slice: &[u8]) -> &OsStr {
-        unsafe { mem::transmute(slice) }
-    }
-    #[inline]
-    fn as_bytes(&self) -> &[u8] {
-        &self.as_inner().inner
-    }
-}