Building glibc with current mainline GCC fails, among other reasons,
because of an error for use of strlen on the nonstring ut_user field.
This patch changes the problem code in getlogin_r to use __strnlen
instead. It also needs to set the trailing NUL byte of the result
explicitly, because of the case where ut_user does not have such a
trailing NUL byte (but the result should always have one).
Tested for x86_64. Also tested that, in conjunction with
<https://sourceware.org/ml/libc-alpha/2017-11/msg00797.html>, it fixes
the build for arm with mainline GCC.
[BZ #22447]
* sysdeps/unix/getlogin_r.c (__getlogin_r): Use __strnlen not
strlen to compute length of ut_user and set trailing NUL byte of
result explicitly.
4bae615022