Mark strlcat() and strlcpy() as weak functions, for libsyslog

The strlcat() and strlcpy() functions are only intended to be used
by syslog.c internally (and syslogd), when building libsyslog.

A user linking with libsyslog may have another library that provides
strlcat() or strlcpy() replacements.  We must therefore mark ours as
weak functions so they can be overridden.

This patch also add a convenience library for libsyslog, to control
the build deps. for libsyslog.  This is where external dependencies
should be addded (explicitly) when syslog.c is updated from NetBSD.
If you add new deps you likely want to mark them too as weak refs.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

lib/strlcat.c

@@ -16,6 +16,10 @@
  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
+#include <config.h>
+#include <compat.h>
+#ifndef HAVE_STRLCAT
+
 #include <sys/types.h>
 #include <string.h>
 
@@ -27,7 +31,7 @@
  * If retval >= dsize, truncation occurred.
  */
 size_t
-strlcat(char *dst, const char *src, size_t dsize)
+__strlcat(char *dst, const char *src, size_t dsize)
 {
 	const char *odst = dst;
 	const char *osrc = src;
@@ -53,3 +57,7 @@ strlcat(char *dst, const char *src, size_t dsize)
 
 	return(dlen + (src - osrc));	/* count does not include NUL */
 }
+
+weak_alias(__strlcat, strlcat);
+
+#endif /* HAVE_STRLCAT */

lib/strlcpy.c

@@ -16,6 +16,10 @@
  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
+#include <config.h>
+#include <compat.h>
+#ifndef HAVE_STRLCPY
+
 #include <sys/types.h>
 #include <string.h>
 
@@ -25,7 +29,7 @@
  * Returns strlen(src); if retval >= dsize, truncation occurred.
  */
 size_t
-strlcpy(char *dst, const char *src, size_t dsize)
+__strlcpy(char *dst, const char *src, size_t dsize)
 {
 	const char *osrc = src;
 	size_t nleft = dsize;
@@ -48,3 +52,7 @@ strlcpy(char *dst, const char *src, size_t dsize)
 
 	return(src - osrc - 1);	/* count does not include NUL */
 }
+
+weak_alias(__strlcpy, strlcpy);
+
+#endif /* HAVE_STRLCPY */

src/.gitignore

@@ -6,5 +6,6 @@ logger
 syslogd
 syslog_tst
 tsyslogd
+libcompat.la
 libsyslog.la
 libsyslog.pc

src/Makefile.am

@@ -19,6 +19,7 @@
 bin_PROGRAMS           = logger
 sbin_PROGRAMS         = syslogd klogd
 lib_LTLIBRARIES       = libsyslog.la
+noinst_LTLIBRARIES    = libcompat.la
 
 AM_CFLAGS             = -W -Wall -Wextra
 AM_CFLAGS            += -Wno-unused-result -Wno-unused-parameter -fno-strict-aliasing
@@ -39,11 +40,15 @@ logger_CPPFLAGS       = $(AM_CPPFLAGS) -D_XOPEN_SOURCE=600
 logger_LDADD          = $(LIBS) $(LIBOBJS)
 logger_LDADD         += libsyslog.la
 
+# Convenience library for libsyslog instead of linking with $(LTLIBOBJS),
+# which would pull in pidfile() and other (strong) symbols as well.
+libcompat_la_SOURCES  = ../lib/strlcpy.c ../lib/strlcat.c
+
 pkgconfigdir          = $(libdir)/pkgconfig
 pkgincludedir         = $(includedir)/syslog
 pkgconfig_DATA        = libsyslog.pc
 pkginclude_HEADERS    = syslog.h
 libsyslog_la_SOURCES  = syslog.c syslog.h
 libsyslog_la_CPPFLAGS = $(AM_CPPFLAGS) -D_XOPEN_SOURCE=600
-libsyslog_la_LIBADD   = $(LTLIBOBJS)
 libsyslog_la_LDFLAGS  = $(AM_LDFLAGS) -version-info 0:0:0
+libsyslog_la_LIBADD   = libcompat.la

src/compat.h

@@ -46,6 +46,17 @@
  */
 #define __UNCONST(a)	((void *)(unsigned long)(const void *)(a))
 
+/*
+ * The functions strlcat() and strlcpy() may be available in either
+ * the C library or another library the user links their application
+ * with.  So we must declare them as "weak" symbols in libsyslog.
+ */
+#ifndef weak_alias
+# define  weak_alias(name, aliasname) _weak_alias (name, aliasname)
+# define _weak_alias(name, aliasname) \
+  extern __typeof (name) aliasname __attribute__ ((weak, alias (#name)))
+#endif
+
 /* Pthread wrapper for BSD LWP mutexes */
 typedef pthread_mutex_t    mutex_t;