build: Make TPM2 support conditional

* configure.ac (HAVE_LIBTSS): New acdefine and am_conditional.
* agent/Makefile.am: (gpg_agent_SOURCES): Move tpm files to ...
(gpg_agent_SOURCES) [HAVE_LIBTSS]: ... here.
* agent/agent.h (divert_tpm2_pksign, divert_tpm2_pkdecrypt)
(divert_tpm2_writekey) [!HAVE_LIBTSS]: Add stub functions.

--
This adds a configure stanza to check for the necessary libtss to
support TPM functions.  If found, the library functions will be
dynamically loaded, meaning that a system built with TPM2 support will
still execute correctly (obviously minus TPM2 support) if installed
without libtss being present.

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

agent/Makefile.am

@@ -51,12 +51,15 @@ gpg_agent_SOURCES = \
 	protect.c \
 	trustlist.c \
 	divert-scd.c \
-	divert-tpm2.c \
-	tpm2.c tpm2.h \
 	cvt-openpgp.c cvt-openpgp.h \
 	call-scd.c \
 	learncard.c
 
+if HAVE_LIBTSS
+gpg_agent_SOURCES += tpm2.c tpm2.h \
+	divert-tpm2.c
+endif
+
 common_libs = $(libcommon)
 commonpth_libs = $(libcommonpth)
 if HAVE_W32CE_SYSTEM

agent/agent.h

@@ -535,6 +535,7 @@ gpg_error_t agent_marktrusted (ctrl_t ctrl, const char *name,
 void agent_reload_trustlist (void);
 
 /*-- divert-tpm2.c --*/
+#ifdef HAVE_LIBTSS
 int divert_tpm2_pksign (ctrl_t ctrl, const char *desc_text,
                         const unsigned char *digest, size_t digestlen, int algo,
                         const unsigned char *shadow_info, unsigned char **r_sig,
@@ -545,6 +546,31 @@ int divert_tpm2_pkdecrypt (ctrl_t ctrl, const char *desc_text,
                            char **r_buf, size_t *r_len, int *r_padding);
 int divert_tpm2_writekey (ctrl_t ctrl, const unsigned char *grip,
                           gcry_sexp_t s_skey);
+#else
+static inline int divert_tpm2_pksign (ctrl_t ctrl, const char *desc_text,
+				      const unsigned char *digest,
+				      size_t digestlen, int algo,
+				      const unsigned char *shadow_info,
+				      unsigned char **r_sig,
+				      size_t *r_siglen)
+{
+  return -EINVAL;
+}
+static inline int divert_tpm2_pkdecrypt (ctrl_t ctrl, const char *desc_text,
+					 const unsigned char *cipher,
+					 const unsigned char *shadow_info,
+					 char **r_buf, size_t *r_len,
+					 int *r_padding)
+{
+  return -EINVAL;
+}
+static inline int divert_tpm2_writekey (ctrl_t ctrl, const unsigned char *grip,
+					gcry_sexp_t s_skey)
+{
+  return -EINVAL;
+}
+#endif
+
 
 
 /*-- divert-scd.c --*/

configure.ac

@@ -100,6 +100,7 @@ have_gnutls=no
 have_sqlite=no
 have_npth=no
 have_libusb=no
+have_libtss=no
 have_system_resolver=no
 gnupg_have_ldap="n/a"
 
@@ -1589,6 +1590,15 @@ fi
 AC_SUBST(NETLIBS)
 AC_SUBST(W32SOCKLIBS)
 
+#
+# TPM libtss library .. don't compile TPM support if we don't have it
+#
+AC_CHECK_LIB(tss, TSS_Create, [have_libtss=yes])
+if test "$have_libtss" = yes; then
+   AC_DEFINE(HAVE_LIBTSS, 1, [Defined if we have TPM2 support library])
+fi
+AM_CONDITIONAL(HAVE_LIBTSS, test "$have_libtss" = yes)
+
 #
 # Setup gcc specific options
 #
@@ -2072,6 +2082,7 @@ echo "
         TLS support:         $use_tls_library
         TOFU support:        $use_tofu
         Tor support:         $show_tor_support
+        TPM support:         $have_libtss
 "
 if test x"$use_regex" != xyes ; then
 echo "