On 24 March 2016 at 17:29, Jeffrey Walton <noloader@xxxxxxxxx> wrote: > On Thu, Mar 24, 2016 at 1:02 PM, Jonathan Wakely <jwakely.gcc@xxxxxxxxx> wrote: >> On 24 March 2016 at 16:43, Jeffrey Walton wrote: >>> There are lots of folks who have experienced the issue; check out >>> http://bugs.debian.org/cgi-bin/pkgreport.cgi?tag=libstdc%2B%2B-cxx11;users=debian-gcc@xxxxxxxxxxxxxxxx. >>> Debian happened to say "f**k it, we'll just recompile everything under >>> the new ABI and be done with it". But they experienced the corner-case >>> issues too. I don't know why they did not consult with the GCC folks. >> >> They did. Rebuilding everything is the right choice. > > It was an incomplete remediation. Debian still has open bugs because > of it, and we are fielding reports because of it. > >>> This step was not obvious to me at all. I don't ever recall having to >>> define a library macro for a library: >>> >>> $ g++ -D_GLIBCXX_USE_CXX11_ABI=0 -c test.cxx -o test-v1.o >>> $ g++ -D_GLIBCXX_USE_CXX11_ABI=1 -c test.cxx -o test-v2.o >>> >>> Naively, because of the blog post on the coexistent implementations, I >>> was looking for an option like -dual-abi to do it for me. >> >> Which is a leap that doesn't in any way follow from a literal reading >> of the blog post! > > Right. We've had similar on other platforms for years and even on > Linux. For example, with Apple, we can build fat binaries. Even the > kernel has FatELF (http://lwn.net/Articles/359070/). > > This situation seems like a perfect application of the technologies, > but it seems to be missing from the solution. Hence the reason I > refrained from the leap, and asked what to do/how do I do it. I've written up the basic steps of how to do what I really, really suggest you do not try to do at http://kayari.org/cxx/dualabi.html The last section explains why a simple compiler switch probably won't work: most code will need non-trivial refactoring to make it work, which a compiler could not do on the fly if you simply provide a command-line option.
