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I am trying to install the gcc 4.8 on a system where gcc 4.3 is installed and used currently. I did some research and knew that it is possible to keep multiple versions of gcc. And it seems for me that using --program-suffix= option is the best solution for me. But my question is, can I install new gcc 4.8 directly into the place where old gcc is installed? Can libraries from both versions be mixed in the same lib directory?
Some more details: the old gcc is installed in /usr/bin, /usr/lib64. If i install new gcc directly to the same location, new libraries will be also installed /usr/lib64. Is this a problem? Will gcc compiler know which library to use when linking?
Many thanks in advance!
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With GCC compilers installed, we can now proceed to install multiple versions of G++ compilers. Alternatively, you can install both GCC and G++ compilers with a single command, as shown below.
Libstdc++ is the standard C++ library. It is needed to compile C++ code (part of GCC is written in C++), but we had to defer its installation when we built gcc-pass1 because it depends on glibc, which was not yet available in /tools. Approximate build time: 0.5 SBU. Required disk space: 878 MB.
Most implementations of libstdc++ depend on libc, so they require it. The C++ standard includes most of the C standard library. So it's kind of a dependency and technically it's part of the C++ standard library.
I'm on Gentoo, which does support installing multiple versions of GCC at the same time. The libraries end up in /usr/lib/gcc/<target>/<version>. Ubuntu seems to install them in the same place, so I'd guess this to be a fairly common setup.
While gcc can apparently figure out the correct version to link against at compile time, the version used at runtime is configured using a file in /etc/ld.so.conf.d. So it might happen that a program gets compiled against one version of the gcc libraries, but executed with another.
If the ld.so.conf.d setting prefers newer versions over older, then this is mostly all right as long as gcc guys didn't introduce a new bug into one of these libraries, and as long as the configuration causes the libraries to be fully backwards-compatible.
In this bug we had a situation where libstdc++ broke backwards compatibility with regard to some C++11 features which were experimental and enabled using a custom configure switch. These things should be rare, but they can happen.
In a related gcc bug report I learned from Jonathan Wakely:
It is totally unsupported (and unlikely to work) to mix C++11 code built with GCC 4.x and 4.y, for any x!=y
Mixing code built with 4.8.x and 4.8.y should work, and does with the default configuration.
So while this setup works in practice on Gentoo, you are on your own if you try this yourself. Particularly since I know of no clean way to ensure that resulting binaries will link against the matching libraries at runtime.
You can try whether --program-suffix affects library names as well. If so, then the SONAME of the newer version libraries should be different from that of the older, helping to get the linking right at runtime. If the library name is unaffected, you could try examining the build system whether you can either change the SONAME of the generated libraries, or have the linker set the RPATH of all the programs it links. I have no experience with either of these approaches.
On Gentoo, /usr/bin/gcc appears to be some kind of wrapper, and the actual programs end up in /usr/<target>/gcc-bin/<version>/gcc and the likes. At least judging from the package web site, Ubuntu doesn't do this for the default version of gcc, although something similar is apparently used for cross-compilation to Android. I guess that setting is the result of a matching --bindir at configure time.
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