On Fri, Dec 01, 2017 at 06:16:26PM -0800, john.hubbard@xxxxxxxxx wrote: > MAP_FIXED has been widely used for a very long time, yet the man > page still claims that "the use of this option is discouraged". I think we should continue to discourage the use of this option, but I'm going to include some of your text in my replacement paragraph ... -Because requiring a fixed address for a mapping is less portable, -the use of this option is discouraged. +The use of this option is discouraged because it forcibly unmaps any +existing mapping at that address. Programs which use this option need +to be aware that their memory map may change significantly from one run to +the next, depending on library versions, kernel versions and random numbers. +In a threaded process, checking the existing mappings can race against +a new dynamic library being loaded, for example in response to another +thread making a library call which causes a PAM module to be loaded. (I don't love this text, in particular "PAM module". I'm going off to use the ATM machine now. Please edit.)
