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