[cfe-dev] clang-tidy false positive cplusplus.NewDeleteLeaks
Tiago Macarios via cfe-dev
cfe-dev at lists.llvm.org
Tue Dec 6 16:54:33 PST 2016
Ok got it. File attached.
Command line used to generate it:
/usr/bin/clang++ \
-E \
-isystem /opt/Qt5.7.0/5.7/gcc_64/include \
-isystem /opt/Qt5.7.0/5.7/gcc_64/include/QtCore \
-fPIC \
-std=c++14 \
-c main.cpp \
-o preprocessed.cpp
To compile:
/usr/bin/clang++ \
--analyze \
-DQT_CORE_LIB \
-DQT_NO_DEBUG \
-fPIC \
-std=c++14 \
-c preprocessed.cpp
Shows the same warning:
In file included from main.cpp:2:
In file included from /opt/Qt5.7.0/5.7/gcc_64/include/QtCore/QObject:1:
/opt/Qt5.7.0/5.7/gcc_64/include/QtCore/qobject.h:343:16: warning: Potential
memory leak
return connectImpl(sender, reinterpret_cast<void **>(&signal),
context, nullptr,
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
On Tue, Dec 6, 2016 at 2:07 PM, Artem Dergachev <noqnoqneo at gmail.com> wrote:
> Could you run `clang` with flag `-E` to obtain a preprocessed file, and
> then demonstrate the problem by running `clang --analyze` (probably with
> some flags) on that file? That'd be really great.
>
> There must be some pointer-escape that we're missing. Hmm, it's not the
> first time Qt turns out to be difficult for the analyzer to handle.
>
> I think i should be able to figure out how to suppress the warning from
> the preprocessed file even if the fix would take some time.
>
>
> On 12/7/16 12:42 AM, Tiago Macarios wrote:
>
>> Hi Artem,
>>
>> Thanks for the email. Could you let me know exactly what you need?
>>
>> If I run clang with the --analyze flag I get a simpler log than the one
>> clang-tidy generates (same problem though):
>>
>> ...
>> [ 75%] Building CXX object CMakeFiles/main.dir/main_automoc.cpp.o
>> In file included from /mnt/e/_working/tidy/main.cpp:2:
>> In file included from /opt/Qt5.7.0/5.7/gcc_64/include/QtCore/QObject:1:
>> /opt/Qt5.7.0/5.7/gcc_64/include/QtCore/qobject.h:343:16: warning:
>> Potential memory leak
>> return connectImpl(sender, reinterpret_cast<void **>(&signal),
>> context, Q_NULLPTR,
>> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> ~~~~~~~~~~~~~~~~
>> 1 warning generated.
>> [100%] Linking CXX executable main
>> clang: warning: CMakeFiles/main.dir/main.cpp.o: 'linker' input unused
>> clang: warning: CMakeFiles/main.dir/main_automoc.cpp.o: 'linker' input
>> unused
>> clang: warning: /opt/Qt5.7.0/5.7/gcc_64/lib/libQt5Core.so.5.7.0:
>> 'linker' input unused
>> clang: warning: -Wl,-rpath,/opt/Qt5.7.0/5.7/gcc_64/lib: 'linker' input
>> unused
>> clang: warning: argument unused during compilation: '-rdynamic'
>> make[3]: Leaving directory '/mnt/e/_working/tidy/build/linux'
>> ...
>>
>>
>>
>> I modified the original cmake file to this:
>>
>> SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} --analyze")
>>
>> set_target_properties(main
>> PROPERTIES
>> CXX_STANDARD 14
>> CXX_EXTENSIONS OFF
>> AUTOMOC ON
>> AUTOUIC ON
>> # CXX_CLANG_TIDY
>> # "clang-tidy"
>> # "-checks=modernize-*,readability-*,performance-*"
>> # "-fix"
>> )
>>
>> On Tue, Dec 6, 2016 at 11:59 AM, Artem Dergachev <noqnoqneo at gmail.com
>> <mailto:noqnoqneo at gmail.com>> wrote:
>>
>> Whoops sorry missed this message!
>>
>> This is (or looks like) a false positive for the clang static
>> analyzer's MallocChecker (clang-tidy runs the analyzer internally,
>> but is not responsible for this checker directly).
>>
>> I think we should investigate that, and a preprocessed file with
>> an -analyze/--analyze command line would speed us up significantly :)
>>
>> On 12/5/16 9:26 PM, Tiago Macarios via cfe-dev wrote:
>>
>> Hi,
>>
>> If this is the wrong mail-list could someone point me to the
>> correct one please?
>>
>> Mac
>>
>> On Thu, Dec 1, 2016 at 5:52 PM, Tiago Macarios
>> <tiagomacarios at gmail.com <mailto:tiagomacarios at gmail.com>
>> <mailto:tiagomacarios at gmail.com
>>
>> <mailto:tiagomacarios at gmail.com>>> wrote:
>>
>> Hi,
>>
>> First time poster so I hope I get the etiquette right.
>>
>> I am trying to use clang-tidy (3.9.1) with a Qt (5.7)
>> project and
>> I am getting a false positive memory leak.
>>
>> Here is the CMake file:
>>
>> cmake_minimum_required(VERSION 3.2)
>> project(main)
>> add_executable(main main.cpp)
>> set_target_properties(main
>> PROPERTIES
>> CXX_STANDARD 14
>> CXX_EXTENSIONS OFF
>> AUTOMOC ON
>> AUTOUIC ON
>> CXX_CLANG_TIDY
>> "clang-tidy"
>> "-checks=modernize-*,readability-*,performance-*"
>> "-fix"
>> )
>> find_package(Qt5Core)
>> target_link_libraries(main Qt5::Core)
>>
>>
>>
>> Here is the main.cpp (it is the minimum amount of code to
>> reproduce the issue, the code itself is brain-dead):
>>
>> #include <QObject>
>>
>> int main(int argc, char *argv[])
>> {
>> QObject a;
>> QObject::connect(&a, &QObject::destroyed, []() {});
>> return 0;
>> }
>>
>>
>>
>> clang-tidy will display the following warning:
>>
>> /opt/Qt5.7.0/5.7/gcc_64/include/QtCore/qobject.h:343:16:
>> warning:
>> Potential memory leak
>> [clang-analyzer-cplusplus.NewDeleteLeaks]
>> return connectImpl(sender, reinterpret_cast<void
>> **>(&signal), context, Q_NULLPTR,
>> ^
>> /mnt/e/_Working/tidy/main.cpp:8:5: note: Calling
>> 'QObject::connect'
>> QObject::connect(&a, &QObject::destroyed, []() {});
>> ^
>> /opt/Qt5.7.0/5.7/gcc_64/include/QtCore/qobject.h:293:16:
>> note:
>> Calling 'QObject::connect'
>> return connect(sender, signal, sender, slot,
>> Qt::DirectConnection);
>> ^
>> /opt/Qt5.7.0/5.7/gcc_64/include/QtCore/qobject.h:308:39:
>> note: '?'
>> condition is true
>> const int SlotArgumentCount =
>> (FunctorArgumentCount >= 0)
>> ? FunctorArgumentCount : 0;
>> ^
>> /opt/Qt5.7.0/5.7/gcc_64/include/QtCore/qobject.h:340:13:
>> note:
>> Left side of '||' is false
>> if (type == Qt::QueuedConnection || type ==
>> Qt::BlockingQueuedConnection)
>> ^
>> /opt/Qt5.7.0/5.7/gcc_64/include/QtCore/qobject.h:340:9: note:
>> Taking false branch
>> if (type == Qt::QueuedConnection || type ==
>> Qt::BlockingQueuedConnection)
>> ^
>> /opt/Qt5.7.0/5.7/gcc_64/include/QtCore/qobject.h:344:28:
>> note:
>> Memory is allocated
>> new QtPrivate::QFunctorSlotObject<Func2, SlotArgumentCount,
>> ^
>> /opt/Qt5.7.0/5.7/gcc_64/include/QtCore/qobject.h:343:16:
>> note:
>> Potential memory leak
>> return connectImpl(sender, reinterpret_cast<void
>> **>(&signal), context, Q_NULLPTR,
>> ^
>>
>>
>>
>> Here is the code it refers to QtCore/qobject.h:343:
>>
>> return connectImpl(sender, reinterpret_cast<void **>(&signal),
>> context, Q_NULLPTR,
>> new QtPrivate::QFunctorSlotObject<Func2,
>> SlotArgumentCount,
>> typename QtPrivate::List_Left<typename SignalType::Arguments,
>> SlotArgumentCount>::Value,
>> typename SignalType::ReturnType>(slot),
>> type, types,
>> &SignalType::Object::staticMetaObject);
>>
>>
>>
>> The object created by that new, does get properly
>> destroyed. This
>> seems to happen at tCore\qobject_impl.h:168:
>>
>> static void impl(int which, QSlotObjectBase *this_,
>> QObject *r, void **a, bool *ret)
>> {
>> switch (which) {
>> case Destroy:
>> delete
>> static_cast<QFunctorSlotObject*>(this_); //HERE
>> break;
>> case Call:
>> FuncType::template call<Args,
>> R>(static_cast<QFunctorSlotObject*>(this_)->function, r, a);
>> break;
>> case Compare: // not implemented
>> case NumOperations:
>> Q_UNUSED(ret);
>> }
>> }
>>
>>
>>
>> From a naive perspective it seems like that false positive
>> leak
>> would be pretty hard to catch. So I guess the best
>> solution (at
>> the moment) would be for me to silence the error. (Please
>> someone
>> correct me if I am wrong).
>>
>> Googling around I found two different ways to silence this
>> false
>> positives:
>> // NOLINT
>> #ifndef __clang_analyzer__
>>
>> I tried to use both in multiple ways, see this SO post:
>> http://stackoverflow.com/questions/40642307/silencing-clang-tidy
>> <http://stackoverflow.com/questions/40642307/silencing-clang-tidy
>> >
>> <http://stackoverflow.com/que
>> stions/40642307/silencing-clang-tidy
>> <http://stackoverflow.com/questions/40642307/silencing-clang-tidy
>> >>
>> But I still haven't figured out a way to silence this
>> error. Maybe
>> someone can help me figure this one out?
>>
>> FYI: QObject::connect is used all over Qt code. So I would
>> rather
>> patch the Qt source files, then have to annotate every call to
>> that function.
>>
>> Mac.
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> _______________________________________________
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>> cfe-dev at lists.llvm.org <mailto:cfe-dev at lists.llvm.org>
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
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>>
>>
>>
>>
>
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