The hard-coded size for the CodeBuffer used in generate_satb_log_enqueue is too small; we can overrun the buffer under certain rare conditions. Specifically, we have seen a case where CBCond was not supported (older Fujitsu hardware) and libjvm.so was loaded far enough away from the code cache that PC-relative addressing could not be used. This case resulted in an overrun of 8 bytes (2 instructions).

The fix for JDK-8166317 appears to have been the "straw that broke the camel's back". The with_frame version of satb_log_enqueue is a few instructions longer than the frameless version, making this issue a regression in practice.