Fix watchOS and visionOS for pread64 and pwrite64 calls

* Refactor apple OSs  to use pwritev and preadv rather pwritev64 and preadv64
* Updated the comments for preadv and pwritev

library/std/src/sys/pal/unix/fd.rs

@@ -45,13 +45,9 @@ const READ_LIMIT: usize = libc::ssize_t::MAX as usize;
 #[cfg(any(
     target_os = "dragonfly",
     target_os = "freebsd",
-    target_os = "ios",
-    target_os = "tvos",
-    target_os = "macos",
     target_os = "netbsd",
     target_os = "openbsd",
-    target_os = "watchos",
-    target_os = "visionos",
+    target_vendor = "apple",
 ))]
 const fn max_iov() -> usize {
     libc::IOV_MAX as usize
@@ -72,17 +68,13 @@ const fn max_iov() -> usize {
     target_os = "dragonfly",
     target_os = "emscripten",
     target_os = "freebsd",
-    target_os = "ios",
-    target_os = "tvos",
     target_os = "linux",
-    target_os = "macos",
     target_os = "netbsd",
     target_os = "nto",
     target_os = "openbsd",
     target_os = "horizon",
     target_os = "vita",
-    target_os = "watchos",
-    target_os = "visionos",
+    target_vendor = "apple",
 )))]
 const fn max_iov() -> usize {
     16 // The minimum value required by POSIX.
@@ -201,13 +193,10 @@ impl FileDesc {
         target_os = "fuchsia",
         target_os = "hurd",
         target_os = "illumos",
-        target_os = "ios",
-        target_os = "tvos",
         target_os = "linux",
-        target_os = "macos",
         target_os = "netbsd",
         target_os = "openbsd",
-        target_os = "watchos",
+        target_vendor = "apple",
     )))]
     pub fn read_vectored_at(&self, bufs: &mut [IoSliceMut<'_>], offset: u64) -> io::Result<usize> {
         io::default_read_vectored(|b| self.read_at(b, offset), bufs)
@@ -241,15 +230,7 @@ impl FileDesc {
         Ok(ret as usize)
     }
 
-    // We support old MacOS and iOS versions that do not have `preadv`. There is
-    // no `syscall` possible in these platform.
-    #[cfg(any(
-        all(target_os = "android", target_pointer_width = "32"),
-        target_os = "ios", // ios 14.0
-        target_os = "tvos", // tvos 14.0
-        target_os = "macos", // macos 11.0
-        target_os = "watchos", // watchos 7.0
-    ))]
+    #[cfg(all(target_os = "android", target_pointer_width = "32"))]
     pub fn read_vectored_at(&self, bufs: &mut [IoSliceMut<'_>], offset: u64) -> io::Result<usize> {
         super::weak::weak!(fn preadv64(libc::c_int, *const libc::iovec, libc::c_int, off64_t) -> isize);
 
@@ -269,6 +250,35 @@ impl FileDesc {
         }
     }
 
+    // We support old MacOS, iOS, watchOS, tvOS and visionOS. `preadv` was added in the following
+    // Apple OS versions:
+    // ios 14.0
+    // tvos 14.0
+    // macos 11.0
+    // watchos 7.0
+    //
+    // These versions may be newer than the minimum supported versions of OS's we support so we must
+    // use "weak" linking.
+    #[cfg(target_vendor = "apple")]
+    pub fn read_vectored_at(&self, bufs: &mut [IoSliceMut<'_>], offset: u64) -> io::Result<usize> {
+        super::weak::weak!(fn preadv(libc::c_int, *const libc::iovec, libc::c_int, off64_t) -> isize);
+
+        match preadv.get() {
+            Some(preadv) => {
+                let ret = cvt(unsafe {
+                    preadv(
+                        self.as_raw_fd(),
+                        bufs.as_mut_ptr() as *mut libc::iovec as *const libc::iovec,
+                        cmp::min(bufs.len(), max_iov()) as libc::c_int,
+                        offset as _,
+                    )
+                })?;
+                Ok(ret as usize)
+            }
+            None => io::default_read_vectored(|b| self.read_at(b, offset), bufs),
+        }
+    }
+
     pub fn write(&self, buf: &[u8]) -> io::Result<usize> {
         let ret = cvt(unsafe {
             libc::write(
@@ -360,13 +370,10 @@ impl FileDesc {
         target_os = "fuchsia",
         target_os = "hurd",
         target_os = "illumos",
-        target_os = "ios",
-        target_os = "tvos",
         target_os = "linux",
-        target_os = "macos",
         target_os = "netbsd",
         target_os = "openbsd",
-        target_os = "watchos",
+        target_vendor = "apple",
     )))]
     pub fn write_vectored_at(&self, bufs: &[IoSlice<'_>], offset: u64) -> io::Result<usize> {
         io::default_write_vectored(|b| self.write_at(b, offset), bufs)
@@ -400,15 +407,7 @@ impl FileDesc {
         Ok(ret as usize)
     }
 
-    // We support old MacOS and iOS versions that do not have `pwritev`. There is
-    // no `syscall` possible in these platform.
-    #[cfg(any(
-        all(target_os = "android", target_pointer_width = "32"),
-        target_os = "ios", // ios 14.0
-        target_os = "tvos", // tvos 14.0
-        target_os = "macos", // macos 11.0
-        target_os = "watchos", // watchos 7.0
-    ))]
+    #[cfg(all(target_os = "android", target_pointer_width = "32"))]
     pub fn write_vectored_at(&self, bufs: &[IoSlice<'_>], offset: u64) -> io::Result<usize> {
         super::weak::weak!(fn pwritev64(libc::c_int, *const libc::iovec, libc::c_int, off64_t) -> isize);
 
@@ -428,6 +427,35 @@ impl FileDesc {
         }
     }
 
+    // We support old MacOS, iOS, watchOS, tvOS and visionOS. `pwritev` was added in the following
+    // Apple OS versions:
+    // ios 14.0
+    // tvos 14.0
+    // macos 11.0
+    // watchos 7.0
+    //
+    // These versions may be newer than the minimum supported versions of OS's we support so we must
+    // use "weak" linking.
+    #[cfg(target_vendor = "apple")]
+    pub fn write_vectored_at(&self, bufs: &[IoSlice<'_>], offset: u64) -> io::Result<usize> {
+        super::weak::weak!(fn pwritev(libc::c_int, *const libc::iovec, libc::c_int, off64_t) -> isize);
+
+        match pwritev.get() {
+            Some(pwritev) => {
+                let ret = cvt(unsafe {
+                    pwritev(
+                        self.as_raw_fd(),
+                        bufs.as_ptr() as *const libc::iovec,
+                        cmp::min(bufs.len(), max_iov()) as libc::c_int,
+                        offset as _,
+                    )
+                })?;
+                Ok(ret as usize)
+            }
+            None => io::default_write_vectored(|b| self.write_at(b, offset), bufs),
+        }
+    }
+
     #[cfg(not(any(
         target_env = "newlib",
         target_os = "solaris",

library/std/src/sys/pal/unix/weak.rs

@@ -28,7 +28,7 @@ use crate::ptr;
 use crate::sync::atomic::{self, AtomicPtr, Ordering};
 
 // We can use true weak linkage on ELF targets.
-#[cfg(not(any(target_os = "macos", target_os = "ios", target_os = "tvos")))]
+#[cfg(all(unix, not(target_vendor = "apple")))]
 pub(crate) macro weak {
     (fn $name:ident($($t:ty),*) -> $ret:ty) => (
         let ref $name: ExternWeak<unsafe extern "C" fn($($t),*) -> $ret> = {
@@ -43,7 +43,7 @@ pub(crate) macro weak {
 }
 
 // On non-ELF targets, use the dlsym approximation of weak linkage.
-#[cfg(any(target_os = "macos", target_os = "ios", target_os = "tvos"))]
+#[cfg(target_vendor = "apple")]
 pub(crate) use self::dlsym as weak;
 
 pub(crate) struct ExternWeak<F: Copy> {