This might be of interest to some. Not all things detected make me worry too much, but there's at least a few interesting bits. http://blog.regehr.org/archives/963 For example, we have this in S_uiv_2buf: uv = -iv; using the obvious types. According to the above tool, this could trigger undefined behaviour (perl 5.18 code): sv.c:2710:7: runtime error: negation of -9223372036854775808 cannot be represented in type 'IV' (aka 'long'); cast to an unsigned type to negate this value to itself --SteffenThread Next