The developers distro of LIBC comes with several different libc versions, one of the most useful ones are the libcXY.logchk one. Replacing the libcXY.dll with it will cause all new LIBC processes to do detailed logging and internal strictness checks. The libc logs are written to libc-<pid>.log files in the current working directory. The format of these files are briefly described by the column headers at the top of each log file.
For most people it is not useful to have internal libc strictness enabled. This can be disabled by setting the env.var. LIBC_STRICT_DISABLED to 1 (or whaterver else, as long as it is set).
It is possible to disable (or enabled) certain log groups using the LIBC_LOGGING env.var. The value of LIBC_LOGGING is a list of groups with an operator '+' or '-' operator in front of them. There is a special group 'all' which can be used to disable or enable all groups. For a correct list of groups, see the source code:
Further details about the logging can be obtained by checking out the source file and header: