Switch libmd wrapper to use dlsym()

Switch from the previous versioned symbol implementation which required
users to also link against the message digest provider explicitly, or
they would fail to find the symbols, to an implementation that loads
the symbols from the linked library providing the functions using
dlsym(), thus preserving backwards compatibility.

configure.ac

@@ -64,9 +64,15 @@ AM_CONDITIONAL([HAVE_LIBTESTU01],
                [test "x$ac_cv_lib_testu01_unif01_CreateExternGenBits" = "xyes"])
 
 saved_LIBS="$LIBS"
+AC_SEARCH_LIBS([dlsym], [dl], [
+  AS_IF([test "x$ac_cv_search_dlsym" != "xnone required"], [
+    LIBBSD_LIBS="$LIBBSD_LIBS $ac_cv_search_dlsym"
+  ])
+], [
+  AC_MSG_ERROR([cannot find required dlsym function])
+])
 AC_SEARCH_LIBS([MD5Update], [md], [
   AS_IF([test "x$ac_cv_search_MD5Update" != "xnone required"], [
-    MD_LIBS="$ac_cv_search_MD5Update"
     LIBBSD_LIBS="$LIBBSD_LIBS $ac_cv_search_MD5Update"
   ])
 ], [
@@ -74,13 +80,11 @@ AC_SEARCH_LIBS([MD5Update], [md], [
 ])
 AC_SEARCH_LIBS([SHA512Update], [md], [
   AS_IF([test "x$ac_cv_search_SHA512Update" != "xnone required"], [
-    MD_LIBS="$ac_cv_search_SHA512Update"
     LIBBSD_LIBS="$LIBBSD_LIBS $ac_cv_search_SHA512Update"
   ])
 ], [
   AC_MSG_ERROR([cannot find required SHA-2 functions in libc or libmd])
 ])
-AC_SUBST([MD_LIBS])
 LIBS="$saved_LIBS"
 
 is_windows=no

src/md5.c

@@ -24,68 +24,100 @@
  * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+#include <stddef.h>
+#include <stdlib.h>
+#include <dlfcn.h>
 #include <md5.h>
-#include "local-link.h"
+
+static void (*libmd_MD5Init)(MD5_CTX *);
+static void (*libmd_MD5Update)(MD5_CTX *, const uint8_t *, size_t);
+static void (*libmd_MD5Pad)(MD5_CTX *);
+static void (*libmd_MD5Final)(uint8_t [MD5_DIGEST_LENGTH], MD5_CTX *);
+static void (*libmd_MD5Transform)(uint32_t [4], const uint8_t [MD5_BLOCK_LENGTH]);
+static char *(*libmd_MD5End)(MD5_CTX *, char *);
+static char *(*libmd_MD5File)(const char *, char *);
+static char *(*libmd_MD5FileChunk)(const char *, char *, off_t, off_t);
+static char *(*libmd_MD5Data)(const uint8_t *, size_t, char *);
+
+static void *
+libmd_loader(const char *symbol)
+{
+	void *func;
+
+	func = dlsym(RTLD_NEXT, symbol);
+	if (func == NULL) {
+		fprintf(stderr,
+		        "libbsd: cannot find wrapped symbol %s in libc or libmd\n",
+		        symbol);
+		abort();
+	}
+
+	return func;
+}
+
+#define libmd_wrapper(symbol) \
+	if (libmd_ ## symbol == NULL) \
+		libmd_ ## symbol = libmd_loader(#symbol)
 
 void
-bsd_MD5Init(MD5_CTX *context)
+MD5Init(MD5_CTX *context)
 {
-	MD5Init(context);
+	libmd_wrapper(MD5Init);
+	libmd_MD5Init(context);
 }
-libbsd_symver_variant(MD5Init, bsd_MD5Init, LIBBSD_0.0);
 
 void
-bsd_MD5Update(MD5_CTX *context, const uint8_t *data, size_t len)
+MD5Update(MD5_CTX *context, const uint8_t *data, size_t len)
 {
-	MD5Update(context, data, len);
+	libmd_wrapper(MD5Update);
+	libmd_MD5Update(context, data, len);
 }
-libbsd_symver_variant(MD5Update, bsd_MD5Update, LIBBSD_0.0);
 
 void
-bsd_MD5Pad(MD5_CTX *context)
+MD5Pad(MD5_CTX *context)
 {
-	MD5Pad(context);
+	libmd_wrapper(MD5Pad);
+	libmd_MD5Pad(context);
 }
-libbsd_symver_variant(MD5Pad, bsd_MD5Pad, LIBBSD_0.0);
 
 void
-bsd_MD5Final(uint8_t digest[MD5_DIGEST_LENGTH], MD5_CTX *context)
+MD5Final(uint8_t digest[MD5_DIGEST_LENGTH], MD5_CTX *context)
 {
-	MD5Final(digest, context);
+	libmd_wrapper(MD5Final);
+	libmd_MD5Final(digest, context);
 }
-libbsd_symver_variant(MD5Final, bsd_MD5Final, LIBBSD_0.0);
 
 void
-bsd_MD5Transform(uint32_t state[4], const uint8_t block[MD5_BLOCK_LENGTH])
+MD5Transform(uint32_t state[4], const uint8_t block[MD5_BLOCK_LENGTH])
 {
-	MD5Transform(state, block);
+	libmd_wrapper(MD5Transform);
+	libmd_MD5Transform(state, block);
 }
-libbsd_symver_variant(MD5Transform, bsd_MD5Transform, LIBBSD_0.0);
 
 char *
-bsd_MD5End(MD5_CTX *context, char *buf)
+MD5End(MD5_CTX *context, char *buf)
 {
-	return MD5End(context, buf);
+	libmd_wrapper(MD5End);
+	return libmd_MD5End(context, buf);
 }
-libbsd_symver_variant(MD5End, bsd_MD5End, LIBBSD_0.0);
 
 char *
-bsd_MD5File(const char *filename, char *buf)
+MD5File(const char *filename, char *buf)
 {
+	libmd_wrapper(MD5File);
 	return MD5File(filename, buf);
 }
-libbsd_symver_variant(MD5File, bsd_MD5File, LIBBSD_0.0);
 
 char *
-bsd_MD5FileChunk(const char *filename, char *buf, off_t offset, off_t length)
+MD5FileChunk(const char *filename, char *buf, off_t offset, off_t length)
 {
-	return MD5FileChunk(filename, buf, offset, length);
+	libmd_wrapper(MD5FileChunk);
+	return libmd_MD5FileChunk(filename, buf, offset, length);
 }
-libbsd_symver_variant(MD5FileChunk, bsd_MD5FileChunk, LIBBSD_0.0);
 
 char *
-bsd_MD5Data(const uint8_t *data, size_t len, char *buf)
+MD5Data(const uint8_t *data, size_t len, char *buf)
 {
-	return MD5Data(data, len, buf);
+	libmd_wrapper(MD5Data);
+	return libmd_MD5Data(data, len, buf);
 }
-libbsd_symver_variant(MD5Data, bsd_MD5Data, LIBBSD_0.0);

test/Makefile.am

@@ -52,8 +52,6 @@ check_PROGRAMS = \
 	vis-openbsd \
 	$(nil)
 
-md5_LDADD = $(LDADD) $(MD_LIBS)
-
 if HAVE_LIBTESTU01
 arc4random_LDADD = $(LDADD) $(TESTU01_LIBS)