__getenvslot
while ((offset = __getenvslot(name, l_name, false)) != -1) {
extern ssize_t __getenvslot(const char *name, size_t l_name, bool allocate);
offset = __getenvslot(name, l_name, false);
offset = __getenvslot(name, l_name, false);
offset = __getenvslot(str, l_name, true);
offset = __getenvslot(name, l_name, true);
r_offset = __getenvslot(name, l_name, false);