From 59ffa607a46135d0d02af72a40914e438e56d586 Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Wed, 22 Oct 2025 06:05:55 -0700
Subject: [PATCH] std.Io.Threaded: fix sending invalid pointer

OS wants valid control pointer even when len is zero
---
 lib/std/Io/Threaded.zig | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/std/Io/Threaded.zig b/lib/std/Io/Threaded.zig
index bce028c13f..4a216c5601 100644
--- a/lib/std/Io/Threaded.zig
+++ b/lib/std/Io/Threaded.zig
@@ -3555,7 +3555,8 @@ fn netSendOne(
         .namelen = addressToPosix(message.address, &addr),
         .iov = (&iovec)[0..1],
         .iovlen = 1,
-        .control = @constCast(message.control.ptr),
+        // OS returns EINVAL if this pointer is invalid even if controllen is zero.
+        .control = if (message.control.len == 0) null else @constCast(message.control.ptr),
         .controllen = @intCast(message.control.len),
         .flags = 0,
     };