https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85142
--- Comment #10 from Jim Wilson <wilson at gcc dot gnu.org> --- The main problem turns out to be your deletion of MULTILIB_REUSE. You get an error if MULTILIB_REUSE refers to directories that aren't in MULTILIB_REQUIRED, but deleting the whole thing is wrong, as this is required to handle the fact that imafdc and gc are the same architecture. Defining MULTILIB_REUSE makes MULTILIB_MATCHES unnecessary. The RISC-V port is using default options specified by configure, so MULTILIB_DEFAULTS appears to be unnecessary. Adding back to your patch MULTILIB_REUSE = \ march.rv64imafdc/mabi.lp64d=march.rv64imafd/mabi.lp64d \ march.rv64imafdc/mabi.lp64d=march.rv64gc/mabi.lp64d \ march.rv64imafdc/mabi.lp64d=march.rv64g/mabi.lp64d I get gamma05:2256$ ./xgcc -B./ --print-multi-lib .; lib64/lp64d;@march=rv64imafdc@mabi=lp64d gamma05:2257$ ./xgcc -B./ --print-multi-dir lib64/lp64d gamma05:2258$ ./xgcc -B./ --print-multi-os-directory ../lib64/lp64d gamma05:2259$ which looks mostly OK. We still have two multilibs according to print-multi-lib though. The default one will never match, because it is identical to the second one, and hence will never be used. We are wasting time building it and installing it. It will install into /usr/lib which we don't want. To get rid of the extra multilib, I need to add multilib defaults again. With that change, I now get gamma05:2331$ ./xgcc -B./ --print-multi-lib .; gamma05:2332$ ./xgcc -B./ --print-multi-dir lib64/lp64d gamma05:2333$ ./xgcc -B./ --print-multi-os-directory ../lib64/lp64d which looks right. Only one copy of the libraries are built, and they get installed in the right place, in ../lib64/lp64d. I'll attach my patch.
