About static libstdc++

[Jonathan Wakely]

On 20 March 2017 at 14:45, Xi Ruoyao wrote:
> Hi all,
>
> At first I would like to tell my sad story:
>
> I'm working on some strange math problem and want to use GCC
> to compile MATLAB MEX files.  Unfortunately, MATLAB rejects recent
> GCC but accepts GCC-4.7.
>
> So I checkouted GCC-4.7.4, compiled it with program-suffix=-4.7.
> I thought with this suffix, I can install it without damage my system
> (only thing has to be done is recreate libstdc++.so link to
> libstdc++.so.6.0.23).
>
> At first it seems OK, but after I put down the math thing and gone to
> hack GCC code, I found out I can't compile GCC anymore...  Then I
> noticed -static-libstdc++ in GCC Makefile and realized my libstdc++.a
> had been replaced by libstdc++ 6.0.17.  At last I had to use GCC-4.7
> to bootstrap GCC trunk version again.
>
> I know I've made a serious mistake to install ancient GCC with only
> a program suffix (w/o a different prefix).  Then I have an idea to
> install libstdc++.a to $prefix/lib/gcc/$arch/$version so that each GCC
> version would be able to use its own static libstdc++ and no version
> would be broke with -static-libstdc++.

There's a configure option that should do something like that:
--enable-version-specific-runtime-libs
but it's broken for multilib:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=32415

> My question is: is this really a good idea or I'm making serious
> mistakes again?

It's probably not a good idea to install to the same prefix as the
system compiler unless you're going to be *very* careful to avoid
conflicts, which is hard to do if you just run "make install" as root.
In theory it can be made to work though.