3 files changed, 25 insertions, 0 deletions

diff --git a/lib/libc/string/memcpy.3 b/lib/libc/string/memcpy.3
index 25a6c359f1da..febc0fa34dd9 100644
--- a/lib/libc/string/memcpy.3
+++ b/lib/libc/string/memcpy.3
@@ -54,6 +54,11 @@ bytes from string
 .Fa src
 to string
 .Fa dst .
+If
+.Fa src
+and
+.Fa dst
+overlap, the results are not defined.
 .Sh RETURN VALUES
 The
 .Fn memcpy
diff --git a/lib/libc/string/strcat.3 b/lib/libc/string/strcat.3
index 802226980d27..a6d0fcef61f0 100644
--- a/lib/libc/string/strcat.3
+++ b/lib/libc/string/strcat.3
@@ -62,6 +62,11 @@ then add a terminating
 The string
 .Fa s
 must have sufficient space to hold the result.
+If
+.Fa s
+and
+.Fa append
+overlap, the results are undefined.
 .Pp
 The
 .Fn strncat
@@ -72,6 +77,11 @@ characters from
 .Fa append ,
 and then adds a terminating
 .Ql \e0 .
+If
+.Fa s
+and
+.Fa append
+overlap, the results are undefined.
 .Sh RETURN VALUES
 The
 .Fn strcat
diff --git a/lib/libc/string/strcpy.3 b/lib/libc/string/strcpy.3
index 4d4a1ee7b3ce..bc555411dde1 100644
--- a/lib/libc/string/strcpy.3
+++ b/lib/libc/string/strcpy.3
@@ -63,6 +63,11 @@ to
 (including the terminating
 .Ql \e0
 character.)
+If
+.Fa src
+and
+.Fa dst
+overlap, the results are undefined.
 .Pp
 The
 .Fn stpncpy
@@ -89,6 +94,11 @@ Otherwise,
 is
 .Em not
 terminated.
+If
+.Fa src
+and
+.Fa dst
+overlap, the results are undefined.
 .Sh RETURN VALUES
 The
 .Fn strcpy