On Wed, 24 Oct 2018 at 16:05, Dennis Clarke wrote: > So the mess seems to be that one must have these include-fixed headers > in place OR not. As I said earlier, when libstdc++ is built it looks at the target headers and checks which features are present in the libc headers. It then assumes that doesn't change. If the host machine's headers change significantly, that can invalidate the configuration that libstdc++ decided on at build time. Due to the significant changes to the libc <math.h> as part of patch 119966-02, I expect you cannot take a libstdc++ built on an unpatched system and run it on a patched system. Rainer should be able to confirm it, but I think this is related to https://gcc.gnu.org/ml/gcc-patches/2016-11/msg00330.html -- that patch is present in all versions of GCC 7 and 8, so if you're seeing problems with those versions then I suspect it's due to differences between <math.h> when libstdc++ was configured and when you're trying to use it. What's not clear from your email is whether you built those versions of GCC on the host machines where you're testing them (and if so, whether it was before or after installing patch 119966-02) or whether you built them on one machine and then copied them to the other hosts.
