We need to inherit -mcpu=power9, -mtune=power9 at least. This does not change baseline, it just enables control via redhat-rpm-config.
Minimal patch: diff --git a/glibc.spec b/glibc.spec index 40b605f..5ee1887 100644 --- a/glibc.spec +++ b/glibc.spec @@ -1095,10 +1095,14 @@ rpm_inherit_flags \ "-march=z15" \ "-march=zEC12" \ "-mbranch-protection=standard" \ + "-mcpu=power8" \ + "-mcpu=power9" \ "-mfpmath=sse" \ "-msse2" \ "-mstackrealign" \ "-mtune=generic" \ + "-mtune=power8" \ + "-mtune=power9" \ "-mtune=z13" \ "-mtune=z14" \ "-mtune=z15" \
Fixed in rawhide via: https://src.fedoraproject.org/rpms/glibc/c/78c735d31e55b33de8ded299ead41a99e0b4966a And 34: https://src.fedoraproject.org/rpms/glibc/c/8f1bd5d8a778711279d6cd405ecf64dab15105ae These changes are no-ops for Fedora, so I didn't bump the Release number.