CODEWITHSUNDEEP
c++linuxgccc++14configure
Bruce Adams
Bruce Adams

Reputation: 5589

How to probe the C++ ABI used by the system version of gcc on the target platform

I have a configuration probe that determines what flags to pass to g++ based on platform and version. I typically use a later version of gcc than the native install version in order to gain access to C++14 features. On older platforms this means I need to add -D_GLIBCXX_USE_CXX11_ABI=0 to use the older C++ ABI or I cannot link with host versions of C++ libraries. However some newer platforms do use the new ABI in which case -D_GLIBCXX_USE_CXX11_ABI=1 (or nothing at all) is required.

I can do this based on the version of the target platform (i.e. the output of lsb_release -a) but I would like a more general method.

I think I'm half way there with compiling a C++ hello world program with the native compiler (as opposed to my later one) but I can't quite figure out how to probe the ABI version. E.g.

>strings hello | grep ABI
.note.ABI-tag
>strings hello | grep CXX
GLIBCXX_3.4

or similarly on the version of libstdc++ used by the hello probe program.

ldd ./hello | grep stdc++ | sed -e 's_.* /_/_' | cut -f 1 -d' ' |xargs strings | grep

Does anyone have any better suggestions?

update: In fact I don't need to do this at all. My real problem was that I had an older version of libstdc++.so hanging around. Compilation picked up one version 6.0.20 and the runtime picked up an incompatible one 6.0.19 (or possibly visa versa). I had an unresolved symbol which I incorrectly blamed on the ABI version. Contrary to popular belief minor versions of libstdc++ aren't always binary compatible. My intention is always to use the exact same version at run and compile time (if not using the host native one).

Upvotes: 8

Views: 7815

Answers (1)

Jonathan Wakely
Jonathan Wakely

Reputation: 171413

Contrary to popular belief minor versions of libstdc++ aren't always binary compatible.

They aren't binary compatible in both directions. libstdc++.so.6.0.20 can be used when libstdc++.so.6.0.19 is required, but not the other way round.

However, prior to GCC 5 the C++11 support was still experimental (i.e. work in progress) and so the ABI of new C++11 components was not stable, so you can't mix C++11/C++14 code compiled with GCC 4.x and GCC 4.y, or GCC 4 and GCC 5. For C++98 code you can mix&match freely (just use the newer libstdc++.so because it's only compatible in one direction).

The details of the major C++11 incompatibilities prior to GCC 5 are documented at https://gcc.gnu.org/wiki/Cxx11AbiCompatibility

Anyway, to answer the now irrelevant question:

I think I'm half way there with compiling a C++ hello world program with the native compiler (as opposed to my later one) but I can't quite figure out how to probe the ABI version

If you can run the native compiler then I don't see what the problem is, just check the default value of the macro:

echo '#include <string>' | g++ -x c++ -E -dM - | fgrep _GLIBCXX_USE_CXX11_ABI

Upvotes: 7

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