[Bug gcov-profile/68080] New: gcov returns negative counts

[Bug gcov-profile/68080] New: gcov returns negative counts

[Pidgeot18 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68080

            Bug ID: 68080
           Summary: gcov returns negative counts
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: gcov-profile
          Assignee: unassigned at gcc dot gnu.org
          Reporter: Pidgeot18 at gmail dot com
  Target Milestone: ---

Created attachment 36576
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36576&action=edit
File to run

(See also bug 67937 for bad things that happen when this occurs).

I finally minimized a test case that causes negative counts to happen. If you
name the attached file TestDeadlockDetector.cpp and run:
 rm -rf *.gcda && c++ --coverage -std=c++11 -pthread -Os
TestDeadlockDetector.cpp && ./a.out && gcov -a -b -p TestDeadlockDetector.gcda
&& grep -- '-[0-9][0-9]*:' TestDeadlockDetector.cpp.gcov

you should usually see ContentionNoDeadlock_thread have negative counts. The
exact count changes from each run (and sometimes, it's not negative).

The -Os is in the c++ command line is definitely required.

[Bug gcov-profile/68080] gcov returns negative counts

[Pidgeot18 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68080

--- Comment #1 from Joshua Cranmer <Pidgeot18 at gmail dot com> ---
For what it's worth:
jcranmer@huitzilopochtli /tmp/gcov-dir $ c++ -v
Using built-in specs.
COLLECT_GCC=c++
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='Debian 5.2.1-22'
--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 --with-arch-32=i586 --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 (Debian 5.2.1-22)