Update glibc at the same time or before upgrading microcode_ctl on Intel Haswell hardware that has hardware transactional memory support. If you upgrade microcode_ctl before upgrading glibc your system will fail to boot and you will need to rescue your system (downgrade microcode_ctl).

Intel errata HSW136 identifies a defect in hardware transactional memory support that requires the user to install a new microcode update to disable this cpu feature. Unfortunately the present method for updating microcode (microcode_ctl) happens too late in the system boot order causing all already running threads that use this feature to die with invalid opcode errors. In order to prevent users from damaging their systems this glibc update completely disables hardware transactional memory support in POSIX threads for Intel devices until such a time as the microcode update can be done earlier in the boot process.