[cfe-dev] clang-tidy false positive cplusplus.NewDeleteLeaks
Artem Dergachev via cfe-dev
cfe-dev at lists.llvm.org
Tue Dec 6 14:07:30 PST 2016
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/questions/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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