The -Wstringop-truncation option new in GCC 8 detects common misuses

of the strncat and strncpy function that may result in truncating
the copied string before the terminating NUL.  To avoid false positive
warnings for correct code that intentionally creates sequences of
characters that aren't guaranteed to be NUL-terminated, arrays that
are intended to store such sequences should be decorated with a new
nonstring attribute.  This change add this attribute to Glibc and
uses it to suppress such false positives.

ChangeLog:
	* misc/sys/cdefs.h (__attribute_nonstring__): New macro.
	* sysdeps/gnu/bits/utmp.h (struct utmp): Use it.
	* sysdeps/unix/sysv/linux/s390/bits/utmp.h (struct utmp): Same.

1 files changed, 6 insertions, 3 deletions

diff --git a/sysdeps/gnu/bits/utmp.h b/sysdeps/gnu/bits/utmp.h
index 2ee11cb706..71c9fa2a9f 100644
--- a/sysdeps/gnu/bits/utmp.h
+++ b/sysdeps/gnu/bits/utmp.h
@@ -59,10 +59,13 @@ struct utmp
 {
   short int ut_type;		/* Type of login.  */
   pid_t ut_pid;			/* Process ID of login process.  */
-  char ut_line[UT_LINESIZE];	/* Devicename.  */
+  char ut_line[UT_LINESIZE]
+    __attribute_nonstring__;	/* Devicename.  */
   char ut_id[4];		/* Inittab ID.  */
-  char ut_user[UT_NAMESIZE];	/* Username.  */
-  char ut_host[UT_HOSTSIZE];	/* Hostname for remote login.  */
+  char ut_user[UT_NAMESIZE]
+    __attribute_nonstring__;	/* Username.  */
+  char ut_host[UT_HOSTSIZE]
+    __attribute_nonstring__;	/* Hostname for remote login.  */
   struct exit_status ut_exit;	/* Exit status of a process marked
 				   as DEAD_PROCESS.  */
 /* The ut_session and ut_tv fields must be the same size when compiled