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
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Reporter: Pavel Fevralev <dllmain@â¦> | Owner: (none)
Type: Bugs | Status: new
Milestone: To Be Determined | Component: None
Version: Boost 1.67.0 | Severity: Problem
Keywords: |
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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.
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