This patch is intended as a companion to the
“Adding buffer overflow detection to string functions”
blog post:

<https://developers.redhat.com/blog/2017/02/02/adding-buffer-overflow-detection-to-string-functions/>

It is relative to libbsd 0.8.3 (commit
9bed430ee30e677d8774e4feba8707507979d62b).

diff --git a/include/bsd/string.h b/include/bsd/string.h
index ee2f953..987abb7 100644
--- a/include/bsd/string.h
+++ b/include/bsd/string.h
@@ -43,6 +43,18 @@ char *strnstr(const char *str, const char *find, size_t str_len);
 void strmode(mode_t mode, char *str);
 
 void explicit_bzero(void *buf, size_t len);
+
+#if defined(__GNUC__) && defined(_FORTIFY_SOURCE) && _FORTIFY_SOURCE > 0
+size_t libbsd_strlcpy_chk(char *dst, const char *src,
+                          size_t siz, size_t dstsiz);
+extern __inline__ __attribute__((__always_inline__, __artificial__))
+size_t
+strlcpy(char *dst, const char *src, size_t siz)
+{
+  return libbsd_strlcpy_chk(dst, src, siz, __builtin_object_size(dst, 1));
+}
+#endif
+
 __END_DECLS
 
 #endif
diff --git a/src/Makefile.am b/src/Makefile.am
index ad83dbf..7ed20ee 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -86,8 +86,10 @@ libbsd_la_SOURCES = \
 	heapsort.c \
 	humanize_number.c \
 	inet_net_pton.c \
+	libbsd_strlcpy_chk.c \
 	local-elf.h \
 	local-link.h \
+	local-string.h \
 	merge.c \
 	nlist.c \
 	pidfile.c \
diff --git a/src/libbsd.map b/src/libbsd.map
index 2b9a3db..5016f50 100644
--- a/src/libbsd.map
+++ b/src/libbsd.map
@@ -136,3 +136,7 @@ LIBBSD_0.7 {
 LIBBSD_0.8 {
     explicit_bzero;
 } LIBBSD_0.7;
+
+LIBBSD_0.9 {
+    libbsd_strlcpy_chk;
+} LIBBSD_0.8;
diff --git a/src/libbsd_strlcpy_chk.c b/src/libbsd_strlcpy_chk.c
new file mode 100644
index 0000000..588f5a0
--- /dev/null
+++ b/src/libbsd_strlcpy_chk.c
@@ -0,0 +1,10 @@
+#include "local-string.h"
+#include <stdlib.h>
+
+size_t
+libbsd_strlcpy_chk(char *dst, const char *src, size_t siz, size_t dstsiz)
+{
+  if (siz > dstsiz)
+    abort();
+  return libbsd_strlcpy_local(dst, src, siz);
+}
diff --git a/src/local-string.h b/src/local-string.h
new file mode 100644
index 0000000..ee381d2
--- /dev/null
+++ b/src/local-string.h
@@ -0,0 +1,9 @@
+#ifndef LIBBSD_LOCAL_STRING_H
+#define LIBBSD_LOCAL_STRING_H
+
+#include <string.h>
+
+size_t libbsd_strlcpy_local(char *dst, const char *src, size_t siz)
+  __attribute__ ((visibility ("hidden")));
+
+#endif
diff --git a/src/strlcpy.c b/src/strlcpy.c
index 1719d35..048765a 100644
--- a/src/strlcpy.c
+++ b/src/strlcpy.c
@@ -17,15 +17,15 @@
  */
 
 #include <sys/types.h>
-#include <string.h>
+#include "local-string.h"
 
 /*
  * Copy src to string dst of size siz.  At most siz-1 characters
  * will be copied.  Always NUL terminates (unless siz == 0).
  * Returns strlen(src); if retval >= siz, truncation occurred.
  */
-size_t
-strlcpy(char *dst, const char *src, size_t siz)
+size_t __attribute__ ((alias("strlcpy")))
+libbsd_strlcpy_local(char *dst, const char *src, size_t siz)
 {
 	char *d = dst;
 	const char *s = src;
@@ -49,3 +49,6 @@ strlcpy(char *dst, const char *src, size_t siz)
 
 	return(s - src - 1);	/* count does not include NUL */
 }
+
+size_t strlcpy(char *dst, const char *src, size_t siz)
+  __attribute__ ((alias("libbsd_strlcpy_local")));