https://www.phoronix.com/scan.php?page=news_item&px=Ryzen-Compiler-Issues It originally looked as an bug on GCC, but last research seems to confirm this is part of the older SMT/uop bug. Remember that earlier engineering samples had uop or the SMT disabled due to this bug. It seems that the bug wasn't completely corrected in retail chips. The problem seems to be traced down to the IRETQ instruction and it is not reproducible when threads are running on different cores. AMD is recommending to disable SMT https://community.amd.com/thread/216084 https://community.amd.com/message/2796982 Surely a microcode update will fix this.