#20350: Work with gcc's new cxx11 abi
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Reporter: vbraun | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-7.2
Component: packages: standard | Resolution:
Keywords: | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
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Comment (by leif):
Replying to [ticket:20350 vbraun]:
> gcc-5 introduces a new cxx11 abi, and linking C++ libraries with
different abi versions will cause missing `std::__cxx11` symbols like
> {{{
> undefined reference to `std::__cxx11::basic_string<char,
std::char_traits<char>, std::allocator<char>
>::push_back(char)@GLIBCXX_3.4.21'
> }}}
GCC's newer libstdc++ comes (by default at least) with a ''dual'' ABI, so
there's no problem when older programs or libraries use the newer one
(e.g. if we upgrade our GCC to 5.x or later and the system GCC is < 5.x).
\\
> This is an issue whenever we build our own gcc; Right now that means
gcc-4.9.3 which only supports the old abi. So linking with any system C++
library will fail, and there are various optional libraries that packages
test for and link when available.
The real problem arises from incompatibilites of (C++) libraries that
expose functions whose signatures contain types like `std::string`,
because the symbol names differ depending on whether the library was
compiled using the old or the new ABI (same of course when compiling code
''using'' such libraries). This leads to linker errors ''if a library and
modules using it'' are compiled with different ABIs (but only if the
modules ''actually use'' such functions).
\\
> Also, gcc-5 system installations may default to the old abi (e.g.
Fedora), so we can't just do a version check. [...]
Well, that's easy to figure out, and we can configure Sage's GCC (>= 5.x)
accordingly: ;-)
{{{
#!sh
GCC_CONFIGURE_CXX_ABI="--with-default-libstdcxx-abi="$(
($CXX -x c++ -S -o - - | awk '/.globl/{print
$2!~/__cxx11/?"gcc4-compatible":"c++11"}') <<EOF
#include <string>
void foo(std::string s){}
EOF
}}}
\\
> Its clear that we must update our gcc to 5 if we ever want to be able to
link to new-abi libraries. Then we could also match the abi by putting
`-D_GLIBCXX_USE_CXX11_ABI=[0|1]` into the `CFLAGS`.
`CXXFLAGS` (if respected by a package) that is, but see above.
--
Ticket URL: <https://trac.sagemath.org/ticket/20350#comment:5>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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