The latest revision of GCC 8.0 adds a -Wstringop-truncation option
to detect common misuses of the strncpy and strncat functions that
may truncate the copy and leave the result without a terminating
nul character.

In testing the implementation with GDB sources on x86_64 I found
a few instances of the warning that are issued for what's safe
but nevertheless not strictly intended uses of the functions
(i.e., to create "bounded" non-nul-terminated copies of a string).
I adjusted the warning to accept some but not all of these use
cases.  The attached patch shows the two instances of the warning
that I had to suppress in GDB.

In general, even though the checker handles some such cases, to
avoid the warning, it's best to use strncpy only with a bound that
reflects the size of the destination, never that of the source.

Martin