fix(libkernel): clear POLLOUT from a hung-up socket in poll on Linux

FreeBSD's pollscan clears POLLOUT whenever POLLHUP is set, for every
descriptor. 64ca6e332 applied that to pipes, but a stream socket whose
peer has closed and whose own sending side is shut down still reported
POLLOUT next to POLLHUP, because Linux's poll sets both. Linux sets
POLLHUP only once both directions are shut, the same condition as
FreeBSD, so poll now clears POLLOUT from any entry that reports POLLHUP
there.

core/libs/prx/libkernel/Socket/src/Udp.cpp

@@ -1834,6 +1834,9 @@ int APS5_VABI poll_nid_postfix(GuestPollDescriptor* descriptors, std::uint32_t c
         if (pipe && (entry.revents & GuestPollError)) entry.revents = static_cast<short>((entry.revents & ~GuestPollError) | GuestPollHangUp);
         if (pipe && (entry.revents & GuestPollHangUp))
             entry.revents = static_cast<short>((entry.revents & ~GuestPollWritable) | (entry.events & GuestPollReadable));
+#ifndef _WIN32
+        if (entry.revents & GuestPollHangUp) entry.revents = static_cast<short>(entry.revents & ~GuestPollWritable);
+#endif
         if (entry.revents) ++ready;
     };
     const auto deadline = std::chrono::steady_clock::now() + std::chrono::milliseconds(timeout < 0 ? 0 : timeout);

core/libs/tests/GuestPoll.cpp

@@ -261,9 +261,36 @@ static void PollsAStreamWhosePeerClosed() {
     for (const int descriptor : {client, server, listener}) Require(close_nid_postfix(descriptor) == 0);
 }
 
+#ifndef _WIN32
+static void PollsAHungUpSocketWithoutPollout() {
+    const int listener = socket_nid_postfix(2, 1, 0);
+    Require(listener >= 0);
+    std::array<unsigned char, 16> address{16, 2, 0, 0, 127, 0, 0, 1};
+    Require(bind_nid_postfix(listener, address.data(), address.size()) == 0);
+    std::uint32_t size = address.size();
+    Require(getsockname_nid_postfix(listener, address.data(), &size) == 0 && listen_nid_postfix(listener, 1) == 0);
+    const int client = socket_nid_postfix(2, 1, 0);
+    Require(client >= 0 && connect_nid_postfix(client, address.data(), address.size()) == 0);
+    const int server = accept_nid_postfix(listener, nullptr, nullptr);
+    Require(server >= 0);
+    Require(close_nid_postfix(client) == 0);
+    char byte = 0;
+    GuestPollDescriptor ended{server, In, 0};
+    Require(poll_nid_postfix(&ended, 1, 1000) == 1);
+    Require(recv_nid_postfix(server, &byte, 1, 0) == 0);
+    Require(shutdown_nid_postfix(server, 1) == 0);
+    GuestPollDescriptor hungUp{server, static_cast<short>(In | Out), 0};
+    Require(poll_nid_postfix(&hungUp, 1, 1000) == 1 && hungUp.revents == (In | Hup));
+    Require(close_nid_postfix(server) == 0 && close_nid_postfix(listener) == 0);
+}
+#endif
+
 int main() {
     PollsUrgentData();
     PollsAStreamWhosePeerClosed();
+#ifndef _WIN32
+    PollsAHungUpSocketWithoutPollout();
+#endif
     const int listener = socket_nid_postfix(2, 1, 0);
     Require(listener >= 0 && listener < 1024);
     std::array<unsigned char, 16> address{16, 2, 0, 0, 127, 0, 0, 1};