On 05 Oct 2015 20:45, Paweł Hajdan, Jr. wrote: > On 10/3/15 4:13 AM, Mike Frysinger wrote: > > Title: GCC 5 Defaults to the New C++11 ABI > > Author: Mike Frysinger <vap...@gentoo.org> > > Content-Type: text/plain > > Posted: 2015-10-02 > > Revision: 1 > > News-Item-Format: 1.0 > > Display-If-Installed: >=sys-devel/gcc-5 > > > > GCC 5 uses the new C++ ABI by default. When building new code, you might > > run > > into link time errors like: > > ...: undefined reference to > > '_ZNSt6chrono12steady_clock3nowEv@GLIBCXX_3.4.17' > > Or you might see linkage failures with "std::__cxx11::string" in the output. > > > > These are signs that you need to rebuild packages using the new C++ ABI. > > You can quickly do so by using revdep-rebuild like so: > > # revdep-rebuild --library 'libstdc\+\+\.so\.6' > > > > For more details, feel free to peruse: > > https://developerblog.redhat.com/2015/02/05/gcc5-and-the-c11-abi/ > > https://blogs.gentoo.org/blueness/2015/03/10/the-c11-abi-incompatibility-problem-in-gentoo/ > > Curious, can one reasonably easy downgrade from GCC 5 back to GCC 4? > > Are there any instructions for that? Is it sufficient to do a similar > revdep-rebuild command? > > In case the downgrade would horribly break systems or be otherwise > highly nontrivial, I'd recommend some note for that.
it's like any other attempt to downgrade an ABI: you're on your own. in Gentoo, we guarantee backwards compatibility, not forward -- this is not specific to GCC. in practice, as long as you don't unmerge gcc-5, you can switch the active compiler to gcc-4.9 and use it, but the runtime libs will be taken from the latest one you have installed (gcc-5). -mike
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