crypto: do an explicit check for nettle pbkdf functions

Support for the PBKDF functions in nettle was not introduced
until version 2.6. Some distros QEMU targets have older
versions and thus lack PBKDF support. Address this by doing
a check in configure for the desired function and then skipping
compilation of the nettle-pbkdf.o module
Reported-by: NWen Congyang <wency@cn.fujitsu.com>
Tested-by: NWen Congyang <wency@cn.fujitsu.com>
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

configure

@@ -308,6 +308,7 @@ gnutls=""
 gnutls_hash=""
 gnutls_rnd=""
 nettle=""
+nettle_kdf="no"
 gcrypt=""
 gcrypt_kdf="no"
 vte=""
@@ -2335,6 +2336,17 @@ if test "$nettle" != "no"; then
         libs_tools="$nettle_libs $libs_tools"
         QEMU_CFLAGS="$QEMU_CFLAGS $nettle_cflags"
         nettle="yes"
+
+        cat > $TMPC << EOF
+#include <nettle/pbkdf2.h>
+int main(void) {
+     pbkdf2_hmac_sha256(8, NULL, 1000, 8, NULL, 8, NULL);
+     return 0;
+}
+EOF
+        if compile_prog "$nettle_cflags" "$nettle_libs" ; then
+            nettle_kdf=yes
+        fi
     else
         if test "$nettle" = "yes"; then
             feature_not_found "nettle" "Install nettle devel"
@@ -4746,6 +4758,7 @@ if test "$nettle" = "yes"; then
 else
     echo "nettle            $nettle"
 fi
+echo "nettle kdf        $nettle_kdf"
 echo "libtasn1          $tasn1"
 echo "VTE support       $vte"
 echo "curses support    $curses"
@@ -5130,6 +5143,9 @@ fi
 if test "$nettle" = "yes" ; then
   echo "CONFIG_NETTLE=y" >> $config_host_mak
   echo "CONFIG_NETTLE_VERSION_MAJOR=${nettle_version%%.*}" >> $config_host_mak
+  if test "$nettle_kdf" = "yes" ; then
+    echo "CONFIG_NETTLE_KDF=y" >> $config_host_mak
+  fi
 fi
 if test "$tasn1" = "yes" ; then
   echo "CONFIG_TASN1=y" >> $config_host_mak

crypto/Makefile.objs

@@ -11,8 +11,8 @@ crypto-obj-y += secret.o
 crypto-obj-$(CONFIG_GCRYPT) += random-gcrypt.o
 crypto-obj-$(if $(CONFIG_GCRYPT),n,$(CONFIG_GNUTLS_RND)) += random-gnutls.o
 crypto-obj-y += pbkdf.o
-crypto-obj-$(CONFIG_NETTLE) += pbkdf-nettle.o
-crypto-obj-$(if $(CONFIG_NETTLE),n,$(CONFIG_GCRYPT_KDF)) += pbkdf-gcrypt.o
+crypto-obj-$(CONFIG_NETTLE_KDF) += pbkdf-nettle.o
+crypto-obj-$(if $(CONFIG_NETTLE_KDF),n,$(CONFIG_GCRYPT_KDF)) += pbkdf-gcrypt.o
 crypto-obj-y += ivgen.o
 crypto-obj-y += ivgen-essiv.o
 crypto-obj-y += ivgen-plain.o