[Boost-bugs] [Boost C++ Libraries] #13619: boost.crc fails to compile with gcc due to undefined behaviour

Subject: [Boost-bugs] [Boost C++ Libraries] #13619: boost.crc fails to compile with gcc due to undefined behaviour
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2018-06-26 19:11:34

#13619: boost.crc fails to compile with gcc due to undefined behaviour
----------------------------------------+---------------------
 Reporter:  Pavel Fevralev <dllmain@…>  |      Owner:  (none)
     Type:  Bugs                        |     Status:  new
Milestone:  To Be Determined            |  Component:  None
  Version:  Boost 1.67.0                |   Severity:  Problem
 Keywords:                              |
----------------------------------------+---------------------
 Boost revision: 62faaa4584e16cd60cd62d5cbb0833954686e89c\\
 Following code is minimal example to reproduce error:
 {{{
  #include <boost/crc.hpp>
  template class boost::crc_optimal<6,6,6,6,0,0>;
  int main() {}
 }}}
 {{{
  $ g++ -std=c++14 -pedantic-errors -I../boost/install-root/include/
 -o/dev/null crc-test.cxx
  In file included from ../boost/install-
 root/include/boost/config.hpp:61:0,
                   from ../boost/install-root/include/boost/crc.hpp:12,
                   from crc-test.cxx:1:
  ../boost/install-root/include/boost/crc.hpp: In instantiation of 'const
 least boost::detail::mask_uint_t<6ul>::sig_bits':
  ../boost/install-root/include/boost/crc.hpp:356:9:   required from 'const
 fast boost::detail::mask_uint_t<6ul>::sig_bits_fast'
  ../boost/install-root/include/boost/crc.hpp:915:41:   required from
 'boost::crc_optimal<Bits, TruncPoly, InitRem, FinalXor, ReflectIn,
 ReflectRem>::value_type boost::crc_optimal<Bits, TruncPoly, InitRem,
 FinalXor, ReflectIn, ReflectRem>::get_interim_remainder() const [with long
 unsigned int Bits = 6ul; typename boost::uint_t<Bits>::fast TruncPoly =
 6u; typename boost::uint_t<Bits>::fast InitRem = 6u; typename
 boost::uint_t<Bits>::fast FinalXor = 6u; bool ReflectIn = false; bool
 ReflectRem = false; boost::crc_optimal<Bits, TruncPoly, InitRem, FinalXor,
 ReflectIn, ReflectRem>::value_type = unsigned char]'
  crc-test.cxx:3:23:   required from here
  ../boost/install-root/include/boost/crc.hpp:350:69: error: left operand
 of shift expression '(-1 << 6ul)' is negative [-fpermissive]
           BOOST_STATIC_CONSTANT( least, sig_bits = (~( ~(least( 0u )) <<
 Bits )) );
 ~~~~~~~~~~~~~~~~~^~~~~~~~~
 }}}
 GCC produce incorrect message: there is no -Werror options or similar, as
 you see. Reason is initialization of static constant in declaration in
 class with expression that is _not_ constant because consists UB(left
 shift of negative value). '0u' literal is unsigned, but promouted to 'int'
 when 'least' is 'unsigned char'. Error is reproductable on release 1.67.0.
 Solution, for example, is make explicit cast of left operand to unsigned
 integral type. GCC information:
 {{{
 $ g++ -v
 Using built-in specs.
 COLLECT_GCC=g++
 COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/6/lto-wrapper
 Target: x86_64-linux-gnu
 Configured with: ../src/configure -v --with-pkgversion='Debian
 6.3.0-18+deb9u1' --with-bugurl=file:///usr/share/doc/gcc-6/README.Bugs
 --enable-languages=c,ada,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr
 --program-suffix=-6 --program-prefix=x86_64-linux-gnu- --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 --enable-default-pie --with-
 system-zlib --disable-browser-plugin --enable-java-awt=gtk --enable-gtk-
 cairo --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-6-amd64/jre --enable-
 java-home --with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-6-amd64 --with-
 jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-6-amd64 --with-arch-
 directory=amd64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --with-
 target-system-zlib --enable-objc-gc=auto --enable-multiarch --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 6.3.0 20170516 (Debian 6.3.0-18+deb9u1)
 }}}

-- 
Ticket URL: <https://svn.boost.org/trac10/ticket/13619>
Boost C++ Libraries <http://www.boost.org/>
Boost provides free peer-reviewed portable C++ source libraries.