[libvirt] [PATCHv2] build: avoid -lgcrypt with newer gnutls

[Eric Blake]

https://bugzilla.redhat.com/show_bug.cgi?id=951637

Newer gnutls uses nettle, rather than gcrypt, which is a lot nicer
regarding initialization.  Yet we were unconditionally initializing
gcrypt even when gnutls wouldn't be using it, and having two crypto
libraries linked into libvirt.so is pointless.

Assume that the switch to gnutls 3.0 is a reliable witness, when
pkg-config is present; otherwise be pessimistic and use gcrypt.

* configure.ac (WITH_GNUTLS): Probe whether to add -lgcrypt, and
define a witness WITH_GNUTLS_GCRYPT.
* src/libvirt.c (virTLSMutexInit, virTLSMutexDestroy)
(virTLSMutexLock, virTLSMutexUnlock, virTLSThreadImpl)
(virGlobalInit): Honor the witness.
* libvirt.spec.in (BuildRequires): Make gcrypt usage conditional,
no longer needed in Fedora 19.

Signed-off-by: Eric Blake <eblake at redhat.com>
---

v2: use second pkg-config invocation rather than ldd to determine
whether gnutls uses gcrypt

 configure.ac    | 27 +++++++++++++++++++--------
 libvirt.spec.in |  2 ++
 src/libvirt.c   | 10 ++++++----
 3 files changed, 27 insertions(+), 12 deletions(-)

diff --git a/configure.ac b/configure.ac
index cc9942a..eb56b63 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1076,12 +1076,19 @@ if test "x$with_gnutls" != "xno"; then
   LIBS="$LIBS $GNUTLS_LIBS"

   GNUTLS_FOUND=no
+  GNUTLS_GCRYPT=no
   if test -x "$PKG_CONFIG" ; then
+    dnl double probe, since we know that gnutls 3.0 switched to nettle instead of
+    dnl gcrypt
     PKG_CHECK_MODULES(GNUTLS, gnutls >= $GNUTLS_REQUIRED,
-      [GNUTLS_FOUND=yes], [GNUTLS_FOUND=no])
+      [GNUTLS_FOUND=yes
+       PKG_CHECK_MODULES([GNUTLS], [gnutls >= 3.0], [], [GNUTLS_GCRYPT=yes])],
+      [GNUTLS_FOUND=no])
   fi
   if test "$GNUTLS_FOUND" = "no"; then
+    dnl pkg-config couldn't help us, assume gcrypt is necessary
     fail=0
+    GNUTLS_GCRYPT=yes
     AC_CHECK_HEADER([gnutls/gnutls.h], [], [fail=1])
     AC_CHECK_LIB([gnutls], [gnutls_handshake],[], [fail=1], [-lgcrypt])

@@ -1098,13 +1105,17 @@ if test "x$with_gnutls" != "xno"; then
       AC_MSG_ERROR([You must install the GnuTLS library in order to compile and run libvirt])
     fi
   else
-    dnl Not all versions of gnutls include -lgcrypt, and so we add
-    dnl it explicitly for the calls to gcry_control/check_version
-    GNUTLS_LIBS="$GNUTLS_LIBS -lgcrypt"
-
-    dnl We're not using gcrypt deprecated features so define
-    dnl GCRYPT_NO_DEPRECATED to avoid deprecated warnings
-    GNUTLS_CFLAGS="$GNUTLS_CFLAGS -DGCRYPT_NO_DEPRECATED"
+    dnl If gnutls linked against -lgcrypt, then we must initialize gcrypt
+    dnl prior to using gnutls.  Newer versions of gnutls use -lnettle, in
+    dnl which case we don't want to drag in gcrypt ourselves.
+    if test "$GNUTLS_GCRYPT" = yes; then
+      GNUTLS_LIBS="$GNUTLS_LIBS -lgcrypt"
+      dnl We're not using gcrypt deprecated features so define
+      dnl GCRYPT_NO_DEPRECATED to avoid deprecated warnings
+      GNUTLS_CFLAGS="$GNUTLS_CFLAGS -DGCRYPT_NO_DEPRECATED"
+      AC_DEFINE_UNQUOTED([WITH_GNUTLS_GCRYPT], 1,
+        [set to 1 if it is known or assumed that GNUTLS uses gcrypt])
+    fi

     dnl gnutls 3.x moved some declarations to a new header
     AC_CHECK_HEADERS([gnutls/crypto.h], [], [], [[
diff --git a/libvirt.spec.in b/libvirt.spec.in
index e0e0004..4320281 100644
--- a/libvirt.spec.in
+++ b/libvirt.spec.in
@@ -422,7 +422,9 @@ BuildRequires: readline-devel
 BuildRequires: ncurses-devel
 BuildRequires: gettext
 BuildRequires: libtasn1-devel
+%if (0%{?rhel} && 0%{?rhel} < 7) || (0%{?fedora} && 0%{?fedora} < 19)
 BuildRequires: libgcrypt-devel
+%endif
 BuildRequires: gnutls-devel
 BuildRequires: libattr-devel
 %if %{with_libvirtd}
diff --git a/src/libvirt.c b/src/libvirt.c
index 8157488..66e8248 100644
--- a/src/libvirt.c
+++ b/src/libvirt.c
@@ -55,7 +55,9 @@
 #include "intprops.h"
 #include "virconf.h"
 #if WITH_GNUTLS
-# include <gcrypt.h>
+# if WITH_GNUTLS_GCRYPT
+#  include <gcrypt.h>
+# endif
 # include "rpc/virnettlscontext.h"
 #endif
 #include "vircommand.h"
@@ -270,7 +272,7 @@ winsock_init(void)
 #endif


-#ifdef WITH_GNUTLS
+#ifdef WITH_GNUTLS_GCRYPT
 static int virTLSMutexInit(void **priv)
 {
     virMutexPtr lock = NULL;
@@ -323,7 +325,7 @@ static struct gcry_thread_cbs virTLSThreadImpl = {
     virTLSMutexUnlock,
     NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL
 };
-#endif
+#endif /* WITH_GNUTLS_GCRYPT */

 /* Helper macros to implement VIR_DOMAIN_DEBUG using just C99.  This
  * assumes you pass fewer than 15 arguments to VIR_DOMAIN_DEBUG, but
@@ -407,7 +409,7 @@ virGlobalInit(void)
         virErrorInitialize() < 0)
         goto error;

-#ifdef WITH_GNUTLS
+#ifdef WITH_GNUTLS_GCRYPT
     /*
      * This sequence of API calls it copied exactly from
      * gnutls 2.12.23 source lib/gcrypt/init.c, with
-- 
1.8.3.1