Member access within misaligned address for type 'UTPSocketKeyData', which requires 8 byte alignment

[Coeur]

What is the issue?

Undefined Behavior Runtime error in libutp, on that line:

libutp/utp_internal.cpp

Line 2574 in c95738b

conn->ctx->utp_sockets->Add(UTPSocketKey(conn->addr, conn->conn_id_recv))->socket = conn;

Thread 6: Misaligned pointer use
Member access within misaligned address 0x0001570734ec for type 'UTPSocketKeyData', which requires 8 byte alignment

It's not a crash, but as it says, it's undefined behavior.
The Xcode documentation to attempt to resolve that is at https://developer.apple.com/documentation/xcode/misaligned-pointer.

Historically, that piece of code is from 2013 (3652544). We kind of branched off libutp from a commit of July 2017 (https://github.com/transmission/libutp/tree/d7daf7f36f64da975fc1b42772f774cbd5ffbbf1), but the official bittorrent repo has been abandoned since then, so no one else is maintaining libutp officially. I still opened an issue at bittorrent#136 some time ago.

Thread 6#0	0x0000000104f08eb4 in __ubsan_on_report ()
#1	0x0000000104f08f68 in __ubsan::UndefinedBehaviorReport::UndefinedBehaviorReport(char const*, __ubsan::Location&, __sanitizer::InternalScopedString&) ()
#2	0x0000000104f048f8 in __ubsan::Diag::~Diag() ()
#3	0x0000000104f06234 in handleTypeMismatchImpl(__ubsan::TypeMismatchData*, unsigned long, __ubsan::ReportOptions) ()
#4	0x0000000104f05ebc in __ubsan_handle_type_mismatch_v1 ()
#5	0x00000001033a44d8 in utp_initialize_socket(UTPSocket*, sockaddr const*, unsigned int, bool, unsigned int, unsigned int, unsigned int) at /Users/User/Developer/transmission/third-party/libutp/utp_internal.cpp:2574
#6	0x00000001033a7cfc in ::utp_connect(utp_socket *, const sockaddr *, socklen_t) at /Users/User/Developer/transmission/third-party/libutp/utp_internal.cpp:2748
#7	0x0000000102bcbfe8 in tr_peerIo::new_outgoing(tr_session*, tr_bandwidth*, tr_address const&, tr_port, std::__1::array<std::byte, 20ul> const&, bool, bool) at /Users/User/Developer/transmission/libtransmission/peer-io.cc:142
#8	0x0000000102bf647c in (anonymous namespace)::connect_helpers::initiateConnection(tr_peerMgr*, tr_swarm*, peer_atom&) at /Users/User/Developer/transmission/libtransmission/peer-mgr.cc:2451
#9	0x0000000102bf3608 in tr_peerMgr::makeNewPeerConnections(unsigned long) at /Users/User/Developer/transmission/libtransmission/peer-mgr.cc:2490
#10	0x0000000102bf2598 in tr_peerMgr::reconnectPulse() at /Users/User/Developer/transmission/libtransmission/peer-mgr.cc:2156
#11	0x0000000102bf39b8 in tr_peerMgr::bandwidthPulse() at /Users/User/Developer/transmission/libtransmission/peer-mgr.cc:2221
#12	0x0000000102bfeac4 in tr_peerMgr::tr_peerMgr(tr_session*)::'lambda'()::operator()() const at /Users/User/Developer/transmission/libtransmission/peer-mgr.cc:689
#13	0x0000000102bfea6c in decltype(std::declval<tr_peerMgr::tr_peerMgr(tr_session*)::'lambda'()&>()()) std::__1::__invoke[abi:v160002]<tr_peerMgr::tr_peerMgr(tr_session*)::'lambda'()&>(tr_peerMgr::tr_peerMgr(tr_session*)::'lambda'()&) at /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.0.sdk/usr/include/c++/v1/__functional/invoke.h:394
#14	0x0000000102bfe8dc in void std::__1::__invoke_void_return_wrapper<void, true>::__call<tr_peerMgr::tr_peerMgr(tr_session*)::'lambda'()&>(tr_peerMgr::tr_peerMgr(tr_session*)::'lambda'()&) at /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.0.sdk/usr/include/c++/v1/__functional/invoke.h:487
#15	0x0000000102bfe870 in std::__1::__function::__alloc_func<tr_peerMgr::tr_peerMgr(tr_session*)::'lambda'(), std::__1::allocator<tr_peerMgr::tr_peerMgr(tr_session*)::'lambda'()>, void ()>::operator()[abi:v160002]() at /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.0.sdk/usr/include/c++/v1/__functional/function.h:185
#16	0x0000000102bfa778 in std::__1::__function::__func<tr_peerMgr::tr_peerMgr(tr_session*)::'lambda'(), std::__1::allocator<tr_peerMgr::tr_peerMgr(tr_session*)::'lambda'()>, void ()>::operator()() at /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.0.sdk/usr/include/c++/v1/__functional/function.h:356
#17	0x0000000102b81754 in std::__1::__function::__value_func<void ()>::operator()[abi:v160002]() const at /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.0.sdk/usr/include/c++/v1/__functional/function.h:510
#18	0x0000000102b7ff90 in std::__1::function<void ()>::operator()() const at /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.0.sdk/usr/include/c++/v1/__functional/function.h:1156
#19	0x00000001030e0ab0 in libtransmission::EvTimer::handleTimer() at /Users/User/Developer/transmission/libtransmission/timer-ev.cc:145
#20	0x00000001030dfd40 in libtransmission::EvTimer::onTimer(int, short, void*) at /Users/User/Developer/transmission/libtransmission/timer-ev.cc:137
#21	0x0000000103286868 in event_persist_closure at /Users/User/Developer/transmission/third-party/libevent/event.c:1623
#22	0x000000010328255c in event_process_active_single_queue at /Users/User/Developer/transmission/third-party/libevent/event.c:1682
#23	0x00000001032621d8 in event_process_active at /Users/User/Developer/transmission/third-party/libevent/event.c:1783
#24	0x000000010325b600 in event_base_loop at /Users/User/Developer/transmission/third-party/libevent/event.c:2006
#25	0x0000000102b7e790 in tr_session_thread_impl::sessionThreadFunc(event_base*) at /Users/User/Developer/transmission/libtransmission/session-thread.cc:245
#26	0x0000000102b83980 in decltype(*std::declval<tr_session_thread_impl*>().*std::declval<void (tr_session_thread_impl::*)(event_base*)>()(std::declval<event_base*>())) std::__1::__invoke[abi:v160002]<void (tr_session_thread_impl::*)(event_base*), tr_session_thread_impl*, event_base*, void>(void (tr_session_thread_impl::*&&)(event_base*), tr_session_thread_impl*&&, event_base*&&) at /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.0.sdk/usr/include/c++/v1/__functional/invoke.h:359
#27	0x0000000102b838ac in void std::__1::__thread_execute[abi:v160002]<std::__1::unique_ptr<std::__1::__thread_struct, std::__1::default_delete<std::__1::__thread_struct>>, void (tr_session_thread_impl::*)(event_base*), tr_session_thread_impl*, event_base*, 2ul, 3ul>(std::__1::tuple<std::__1::unique_ptr<std::__1::__thread_struct, std::__1::default_delete<std::__1::__thread_struct>>, void (tr_session_thread_impl::*)(event_base*), tr_session_thread_impl*, event_base*>&, std::__1::__tuple_indices<2ul, 3ul>) at /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.0.sdk/usr/include/c++/v1/thread:288
#28	0x0000000102b82770 in void* std::__1::__thread_proxy[abi:v160002]<std::__1::tuple<std::__1::unique_ptr<std::__1::__thread_struct, std::__1::default_delete<std::__1::__thread_struct>>, void (tr_session_thread_impl::*)(event_base*), tr_session_thread_impl*, event_base*>>(void*) at /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.0.sdk/usr/include/c++/v1/thread:299
#29	0x0000000104b61628 in _pthread_start ()

Which application of Transmission?

macOS app

Which version of Transmission?

4.1.0-dev (76166d8fa7)

[ckerr]

@Coeur, @mikedld, @tearfur PR is up @ #13

This is largish diff and the libutp repo has no tests. If / when we merge this and start using in Transmission, we will want a decent amount of time for nightly build users to test it out.

[Coeur]

So, that issue was easily reproducible in current Transmission main (transmission/transmission@a575be7), which is based on c95738b.
Trying with newer libutp now (4ed4d43)... and the misaligned address undefined behavior is gone. 👍 🎉