[Bug sanitizer/68777] New: [UBSAN] Spurious warning with C++11 lambdas ("member call on null pointer")

["neil.conway at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68777

            Bug ID: 68777
           Summary: [UBSAN] Spurious warning with C++11 lambdas ("member
                    call on null pointer")
           Product: gcc
           Version: 5.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: sanitizer
          Assignee: unassigned at gcc dot gnu.org
          Reporter: neil.conway at gmail dot com
                CC: dodji at gcc dot gnu.org, dvyukov at gcc dot gnu.org,
                    jakub at gcc dot gnu.org, kcc at gcc dot gnu.org
  Target Milestone: ---

Created attachment 36948
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36948&action=edit
Reduced test case.

$ vi sync-test.cpp
vagrant@vagrant-ubuntu-wily-64:~$ g++ -fsanitize=undefined -std=c++11 -Wall -W
sync-test.cpp -o sync_test
vagrant@vagrant-ubuntu-wily-64:~$ ./sync_test
vagrant@vagrant-ubuntu-wily-64:~$ g++ -DUSE_LAMBDA -fsanitize=undefined
-std=c++11 -Wall -W sync-test.cpp -o sync_test
vagrant@vagrant-ubuntu-wily-64:~$ ./sync_test
sync-test.cpp:25:6: runtime error: member call on null pointer of type 'const
struct __lambda0'
    #0 0x400832 in Synchronized<int>
my_synchronize_warns<int>(int*)::{lambda(int*)#1}::_FUN(int*)
(/home/vagrant/sync_test+0x400832)
    #1 0x400a79 in Synchronized<int>::Synchronized(int*, void (*)(int*), void
(*)(int*)) (/home/vagrant/sync_test+0x400a79)
    #2 0x40091d in Synchronized<int> my_synchronize_warns<int>(int*)
(/home/vagrant/sync_test+0x40091d)
    #3 0x4007df in main (/home/vagrant/sync_test+0x4007df)
    #4 0x7fc3708eca3f in __libc_start_main
(/lib/x86_64-linux-gnu/libc.so.6+0x20a3f)
    #5 0x4006e8 in _start (/home/vagrant/sync_test+0x4006e8)

sync-test.cpp:26:6: runtime error: member call on null pointer of type 'const
struct __lambda1'
    #0 0x400880 in Synchronized<int>
my_synchronize_warns<int>(int*)::{lambda(int*)#2}::_FUN(int*)
(/home/vagrant/sync_test+0x400880)
    #1 0x4009a6 in Synchronized<int>::~Synchronized()
(/home/vagrant/sync_test+0x4009a6)
    #2 0x4007eb in main (/home/vagrant/sync_test+0x4007eb)
    #3 0x7fc3708eca3f in __libc_start_main
(/lib/x86_64-linux-gnu/libc.so.6+0x20a3f)
    #4 0x4006e8 in _start (/home/vagrant/sync_test+0x4006e8)

$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/5/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 5.2.1-22ubuntu2'
--with-bugurl=file:///usr/share/doc/gcc-5/README.Bugs
--enable-languages=c,ada,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-5 --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=new --enable-gnu-unique-object
--disable-vtable-verify --enable-libmpx --enable-plugin --with-system-zlib
--disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-5-amd64/jre --enable-java-home
--with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-5-amd64
--with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-5-amd64
--with-arch-directory=amd64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar
--enable-objc-gc --enable-multiarch --disable-werror --with-arch-32=i686
--with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib
--with-tune=generic --enable-checking=release --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 5.2.1 20151010 (Ubuntu 5.2.1-22ubuntu2)
$ uname -a
Linux vagrant-ubuntu-wily-64 4.2.0-19-generic #23-Ubuntu SMP Wed Nov 11
11:39:30 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux


As far as I can see, my_synchronize_warns() and my_synchronize_no_warning() are
equivalent.