Commit e098b287e1

@@ -1196,13 +1196,26 @@ pub const File = struct {
         }
     }
 
-    /// The `iovecs` parameter is mutable because this function needs to mutate the fields in
-    /// order to handle partial writes from the underlying OS layer.
+    /// The `iovecs` parameter is mutable because:
+    /// * This function needs to mutate the fields in order to handle partial
+    ///   writes from the underlying OS layer.
+    /// * The OS layer expects pointer addresses to be inside the application's address space
+    ///   even if the length is zero. Meanwhile, in Zig, slices may have undefined pointer
+    ///   addresses when the length is zero. So this function modifies the iov_base fields
+    ///   when the length is zero.
     /// See https://github.com/ziglang/zig/issues/7699
     /// See equivalent function: `std.net.Stream.writevAll`.
     pub fn writevAll(self: File, iovecs: []os.iovec_const) WriteError!void {
         if (iovecs.len == 0) return;
 
+        // We use the address of this local variable for all zero-length
+        // vectors so that the OS does not complain that we are giving it
+        // addresses outside the application's address space.
+        var garbage: [1]u8 = undefined;
+        for (iovecs) |*v| {
+            if (v.iov_len == 0) v.iov_base = &garbage;
+        }
+
         var i: usize = 0;
         while (true) {
             var amt = try self.writev(iovecs[i..]);

@@ -767,8 +767,8 @@ pub fn read(fd: fd_t, buf: []u8) ReadError!usize {
 /// * Windows
 /// On these systems, the read races with concurrent writes to the same file descriptor.
 ///
-/// This function assumes that all zero-length vectors have a pointer within the address
-/// space of the application.
+/// This function assumes that all vectors, including zero-length vectors, have
+/// a pointer within the address space of the application.
 pub fn readv(fd: fd_t, iov: []const iovec) ReadError!usize {
     if (builtin.os.tag == .windows) {
         // TODO improve this to use ReadFileScatter
@@ -1170,6 +1170,9 @@ pub fn write(fd: fd_t, bytes: []const u8) WriteError!usize {
 /// used to perform the I/O. `error.WouldBlock` is not possible on Windows.
 ///
 /// If `iov.len` is larger than `IOV_MAX`, a partial write will occur.
+///
+/// This function assumes that all vectors, including zero-length vectors, have
+/// a pointer within the address space of the application.
 pub fn writev(fd: fd_t, iov: []const iovec_const) WriteError!usize {
     if (builtin.os.tag == .windows) {
         // TODO improve this to use WriteFileScatter