It looks like we found out why we weren't using `%zu` before: ``` 17:55:39 In file included from src/or/or.h:72:0, 17:55:39 from src/or/circuitlist.c:54: 17:55:39 src/or/circuitlist.c: In function 'circuits_handle_oom': 17:55:39 src/or/circuitlist.c:2407:26: error: unknown conversion type character 'z' in format [-Werror=format=] 17:55:39 log_notice(LD_GENERAL, "We're low on memory (cell queues total alloc: %zu," 17:55:39 ^ 17:55:39 ./src/common/torlog.h:232:45: note: in definition of macro 'log_notice' 17:55:39 log_fn_(LOG_NOTICE, domain, __FUNCTION__, args, ##__VA_ARGS__) 17:55:39 ^~~~ 17:55:39 src/or/circuitlist.c:2407:26: error: unknown conversion type character 'z' in format [-Werror=format=] 17:55:39 log_notice(LD_GENERAL, "We're low on memory (cell queues total alloc: %zu," 17:55:39 ^ ``` (from https://jenkins.torproject.org/job/tor-ci-mingwcross-master/1577/ARCHITECTURE=amd64,SUITE=stretch/consoleFull) In theory we can select a more c99 one with `__USE_MINGW_ANSI_STDIO`, but that would change our stdio everywhere. (Which is a little scary.) We could also define a PRIsz macro that has the correct format for whatever compiler we are using. That might be a better choice.