type-context: disable clang-tidy UndefinedBinaryOperatorResult error

ryanofsky · ryanofsky · commit 80f1c2ef3242 · 2025-06-20T08:25:43.000-04:00
Reported by fanquake <fanquake@gmail.com> bitcoin/bitcoin#31802 (comment) https://cirrus-ci.com/task/6552721135763456 https://api.cirrus-ci.com/v1/task/6552721135763456/logs/ci.log Error is spurious and comes from kj/async-inl.h and it seems to be shown because clang-tidy considers this error to come from "main file" of the translation unit (see https://clang.llvm.org/extra/clang-tidy/, https://stackoverflow.com/a/47611238, https://reviews.llvm.org/D26418) even though this is not the case. Even though the header is included via -isystem and clang-tidy --dump-config shows "SystemHeaders: false" the error is still shown. I also tried to suppress the error by editing .clang-tidy to include: HeaderFilterRegex: '.*' ExcludeHeaderFilterRegex: '.*/include/kj/async-inl\.h$' and many variations but the error is always shown, I assume because ExcludeHeaderFilterRegex does not ignore the isInMainFile condition (https://github.com/llvm/llvm-project/pull/91400/files). Adding NOLINT to the getLocalServer() line in types-context.h at the boundary between libmultiprocess and Cap'n Proto code also does not suppress the error. It does suppress clang-tidy "note:" lines below the NOLINT point in the call stack, making the error messages shorter, but the only way of suppressing the error completely seems to be either adding NOLINT inside the Cap'n Proto header, which requires a patch, or adding it to all top-level callers of the getLocalServer() function in .cpp files, which seems impractical and overbroad, and I didn't attempt. The actual warning is a false positive that comes from ABI-specific code in Cap'n Proto that gets the starting function address (that can be passed to addr2line) from a lambda or function object. This code calls a helper to get the starting function address from a pointer-to-member-function, which in this case is the the operator() member function. That code handles pointers to virtual member functions, so it checks if the pointer is virtual by testing its low-order bit, and if set, assumes the first bytes of the object are a vtable pointer, and does pointer arithmetic with the vtable address. Clang-tidy complains about this because it does not know the vtable address is valid, assuming incorrectly it is a "garbage value". I wrote patch adding NOLINT to Cap'n Proto in capnproto/capnproto#2334 which could be good long-term fix for this issue if clang-tidy does not provide a better way of suppressing the error. Complete error output is: /nix/store/46kiq9naswgbqfc14kc9nxcbgd0rv0m2-capnproto-1.1.0/include/kj/async-inl.h:609:37: error: The left operand of '+' is a garbage value [clang-analyzer-core.UndefinedBinaryOperatorResult,-warnings-as-errors] 609 | return *(void**)(*(char**)obj + voff); | ^ build/test/mp/test/foo.capnp.proxy-server.c++:93:12: note: Calling 'serverInvoke<mp::ProxyServer<mp::test::messages::FooFn>, capnp::CallContext<mp::test::messages::FooFn::CallParams, mp::test::messages::FooFn::CallResults>, mp::ServerField<0, mp::Accessor<mp::foo_fields::Context, 17>, mp::ServerRet<mp::Accessor<mp::foo_fields::Result, 2>, mp::ServerCall>>>' 93 | return serverInvoke(*this, call_context, MakeServerField<0, Accessor<foo_fields::Context, FIELD_IN | FIELD_BOXED>>(Make<ServerRet, Accessor<foo_fields::Result, FIELD_OUT>>(ServerCall()))); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ include/mp/proxy-types.h:739:16: note: Calling 'ReplaceVoid<(lambda at include/mp/proxy-types.h:739:28), (lambda at include/mp/proxy-types.h:740:13)>' 739 | return ReplaceVoid([&]() { return fn.invoke(server_context, ArgList()); }, | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 740 | [&]() { return kj::Promise<CallContext>(kj::mv(call_context)); }) | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ include/mp/proxy-types.h:700:19: note: 'is_same_v' is false 700 | if constexpr (std::is_same_v<decltype(fn()), void>) { | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ include/mp/proxy-types.h:700:5: note: Taking false branch 700 | if constexpr (std::is_same_v<decltype(fn()), void>) { | ^ include/mp/proxy-types.h:704:16: note: Calling 'operator()' 704 | return fn(); | ^~~~ include/mp/proxy-types.h:739:43: note: Calling 'ServerField::invoke' 739 | return ReplaceVoid([&]() { return fn.invoke(server_context, ArgList()); }, | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ include/mp/proxy-types.h:563:16: note: Calling 'PassField<mp::Accessor<mp::foo_fields::Context, 17>, mp::ServerInvokeContext<mp::ProxyServer<mp::test::messages::FooFn>, capnp::CallContext<mp::test::messages::FooFn::CallParams, mp::test::messages::FooFn::CallResults>>, mp::ServerRet<mp::Accessor<mp::foo_fields::Result, 2>, mp::ServerCall>, mp::TypeList<>>' 563 | return PassField<Accessor>(Priority<2>(), | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 564 | typename Split<argc, ArgTypes>::First(), | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 565 | server_context, | ~~~~~~~~~~~~~~~ 566 | this->parent(), | ~~~~~~~~~~~~~~~ 567 | typename Split<argc, ArgTypes>::Second(), | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 568 | std::forward<Args>(args)...); | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ include/mp/type-context.h:151:12: note: Calling 'CapabilityServerSet::getLocalServer' 151 | return server.m_context.connection->m_threads.getLocalServer(thread_client) | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ /nix/store/46kiq9naswgbqfc14kc9nxcbgd0rv0m2-capnproto-1.1.0/include/capnp/capability.h:1274:10: note: Calling 'Promise::then' 1274 | return getLocalServerInternal(client) | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 1275 | .then([](void* server) -> kj::Maybe<typename T::Server&> { | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 1276 | if (server == nullptr) { | ~~~~~~~~~~~~~~~~~~~~~~~~ 1277 | return nullptr; | ~~~~~~~~~~~~~~~ 1278 | } else { | ~~~~~~~~ 1279 | return *reinterpret_cast<typename T::Server*>(server); | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 1280 | } | ~ 1281 | }); | ~~ /nix/store/46kiq9naswgbqfc14kc9nxcbgd0rv0m2-capnproto-1.1.0/include/kj/async-inl.h:1295:32: note: Calling 'GetFunctorStartAddress::apply' 1295 | void* continuationTracePtr = _::GetFunctorStartAddress<_::FixVoid<T>&&>::apply(func); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ /nix/store/46kiq9naswgbqfc14kc9nxcbgd0rv0m2-capnproto-1.1.0/include/kj/async-inl.h:677:12: note: Calling 'PtmfHelper::apply' 677 | return PtmfHelper::from<ReturnType, Decay<Func>, ParamTypes...>( | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 678 | &Decay<Func>::operator()).apply(&func); | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ /nix/store/46kiq9naswgbqfc14kc9nxcbgd0rv0m2-capnproto-1.1.0/include/kj/async-inl.h:606:9: note: Assuming the condition is true 606 | if (voff & 1) { | ^~~~~~~~ /nix/store/46kiq9naswgbqfc14kc9nxcbgd0rv0m2-capnproto-1.1.0/include/kj/async-inl.h:606:5: note: Taking true branch 606 | if (voff & 1) { | ^ /nix/store/46kiq9naswgbqfc14kc9nxcbgd0rv0m2-capnproto-1.1.0/include/kj/async-inl.h:609:37: note: The left operand of '+' is a garbage value 609 | return *(void**)(*(char**)obj + voff); | ~~~~~~~~~~~~ ^
diff --git a/.clang-tidy b/.clang-tidy
@@ -26,8 +26,9 @@ performance-*,
 readability-const-return-type,
 readability-redundant-declaration,
 readability-redundant-string-init,
-clang-analyzer-core.StackAddressEscape,
-clang-analyzer-optin.core.EnumCastOutOfRange,
+clang-analyzer-core.*,
+-clang-analyzer-core.UndefinedBinaryOperatorResult,
+clang-analyzer-optin.core.*,
 '
 HeaderFilterRegex: '.'
 WarningsAsErrors: '*'
