[Bug c++/56066] g++ generates strong symbols conflicting with C99 extern inline code on Windows

["solomon.gibbs.lists at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56066

Solomon Gibbs <solomon.gibbs.lists at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|FIXED                       |---

--- Comment #5 from Solomon Gibbs <solomon.gibbs.lists at gmail dot com> ---
Sorry, I missed the request for more information.

This is still broken for me under 4.8.1. 

In a nutshell, I think that differing assumptions about inline functions made
by g++ and gcc are carrying over into object file output and preventing
linking. 

Working from a shared header with a non-static inline function, gcc explicitly
creates an implementation at the location of an "extern inline ...". On the
other hand, g++ creates an implementation in every unit where the header was
included, intending to throw away redundant definitions at link time. 

This gives us a definition in the C unit and the C++ unit. However, for some
reason, possibly related to the difference in COFF data, the linker is unable
to determine that the definitions are truly identical as it would if they both
came from a non-static C++ inline.

One workaround is to prevent the C++ definition from being created using the
gnu_inline function attribute.


I updated the original attachment to show the workaround and added a Makefile.
Since this requires a shared header, C and C++ units to manifest, I did not
paste all three files into the comment, but left them in the attachment
archive. Please let me know if you still need something else to reproduce the
issue.

The relevant output is obtained from objdump as:

$ objdump -x app-broken.o |grep -B1 -e 'COMDAT _problem_function'
  3 .text$problem_function 0000000c  00000000  00000000  00000180  2**2
                  CONTENTS, ALLOC, LOAD, READONLY, CODE, LINK_ONCE_DISCARD
(COMDAT _problem_function 4)


$ gcc -v
Using built-in specs.
COLLECT_GCC=C:\opt\MinGW-w64\x86-posix-dwarf\bin\gcc.exe
COLLECT_LTO_WRAPPER=c:/opt/mingw-w64/x86-posix-dwarf/bin/../libexec/gcc/i686-w64-mingw32/4.8.1/lto-wrapper.exe
Target: i686-w64-mingw32
Configured with: ../../../src/gcc-4.8.1/configure --host=i686-w64-mingw32
--build=i686-w64-mingw32 --target=i686-w64-mingw32 --prefix=/mingw32
--with-sysroot=/tmp/x32-481-posix-dwarf-r5/mingw32 --enable-shared
--enable-static --disable-multilib
--enable-languages=ada,c,c++,fortran,objc,obj-c++,lto
--enable-libstdcxx-time=yes --enable-threads=posix --enable-libgomp
--enable-lto --enable-graphite --enable-checking=release
--enable-fully-dynamic-string --enable-version-specific-runtime-libs
--disable-sjlj-exceptions --with-dwarf2 --disable-isl-version-check
--disable-cloog-version-check --disable-libstdcxx-pch --disable-libstdcxx-debug
--enable-bootstrap --disable-rpath --disable-win32-registry --disable-nls
--disable-werror --disable-symvers --with-gnu-as --with-gnu-ld --with-arch=i686
--with-tune=generic --with-libiconv --with-system-zlib
--with-gmp=/tmp/mingw-prereq/i686-w64-mingw32-static
--with-mpfr=/tmp/mingw-prereq/i686-w64-mingw32-static
--with-mpc=/tmp/mingw-prereq/i686-w64-mingw32-static
--with-isl=/tmp/mingw-prereq/i686-w64-mingw32-static
--with-cloog=/tmp/mingw-prereq/i686-w64-mingw32-static
--enable-cloog-backend=isl --with-pkgversion='rev5, Built by MinGW-W64 project'
--with-bugurl=http://sourceforge.net/projects/mingw-w64 CFLAGS='-O2 -pipe
-I/tmp/x32-481-posix-dwarf-r5/libs/include -I/tmp/mingw-prereq/x32-zlib/include
-I/tmp/mingw-prereq/i686-w64-mingw32-static/include' CXXFLAGS='-O2 -pipe
-I/tmp/x32-481-posix-dwarf-r5/libs/include -I/tmp/mingw-prereq/x32-zlib/include
-I/tmp/mingw-prereq/i686-w64-mingw32-static/include' CPPFLAGS= LDFLAGS='-pipe
-L/tmp/x32-481-posix-dwarf-r5/libs/lib -L/tmp/mingw-prereq/x32-zlib/lib
-L/tmp/mingw-prereq/i686-w64-mingw32-static/lib
-L/tmp/x32-481-posix-dwarf-r5/mingw32/opt/lib -Wl,--large-address-aware'
Thread model: posix
gcc version 4.8.1 (rev5, Built by MinGW-W64 project)


$ g++ -v
Using built-in specs.
COLLECT_GCC=C:\opt\MinGW-w64\x86-posix-dwarf\bin\g++.exe
COLLECT_LTO_WRAPPER=c:/opt/mingw-w64/x86-posix-dwarf/bin/../libexec/gcc/i686-w64-mingw32/4.8.1/lto-wrapper.exe
Target: i686-w64-mingw32
Configured with: ../../../src/gcc-4.8.1/configure --host=i686-w64-mingw32
--build=i686-w64-mingw32 --target=i686-w64-mingw32 --prefix=/mingw32
--with-sysroot=/tmp/x32-481-posix-dwarf-r5/mingw32 --enable-shared
--enable-static --disable-multilib
--enable-languages=ada,c,c++,fortran,objc,obj-c++,lto
--enable-libstdcxx-time=yes --enable-threads=posix --enable-libgomp
--enable-lto --enable-graphite --enable-checking=release
--enable-fully-dynamic-string --enable-version-specific-runtime-libs
--disable-sjlj-exceptions --with-dwarf2 --disable-isl-version-check
--disable-cloog-version-check --disable-libstdcxx-pch --disable-libstdcxx-debug
--enable-bootstrap --disable-rpath --disable-win32-registry --disable-nls
--disable-werror --disable-symvers --with-gnu-as --with-gnu-ld --with-arch=i686
--with-tune=generic --with-libiconv --with-system-zlib
--with-gmp=/tmp/mingw-prereq/i686-w64-mingw32-static
--with-mpfr=/tmp/mingw-prereq/i686-w64-mingw32-static
--with-mpc=/tmp/mingw-prereq/i686-w64-mingw32-static
--with-isl=/tmp/mingw-prereq/i686-w64-mingw32-static
--with-cloog=/tmp/mingw-prereq/i686-w64-mingw32-static
--enable-cloog-backend=isl --with-pkgversion='rev5, Built by MinGW-W64 project'
--with-bugurl=http://sourceforge.net/projects/mingw-w64 CFLAGS='-O2 -pipe
-I/tmp/x32-481-posix-dwarf-r5/libs/include -I/tmp/mingw-prereq/x32-zlib/include
-I/tmp/mingw-prereq/i686-w64-mingw32-static/include' CXXFLAGS='-O2 -pipe
-I/tmp/x32-481-posix-dwarf-r5/libs/include -I/tmp/mingw-prereq/x32-zlib/include
-I/tmp/mingw-prereq/i686-w64-mingw32-static/include' CPPFLAGS= LDFLAGS='-pipe
-L/tmp/x32-481-posix-dwarf-r5/libs/lib -L/tmp/mingw-prereq/x32-zlib/lib
-L/tmp/mingw-prereq/i686-w64-mingw32-static/lib
-L/tmp/x32-481-posix-dwarf-r5/mingw32/opt/lib -Wl,--large-address-aware'
Thread model: posix
gcc version 4.8.1 (rev5, Built by MinGW-W64 project)