build: set library version to 0.0.0 explicitly

Makefile.am

@@ -88,7 +88,7 @@ endif
 libsecp256k1_la_SOURCES = src/secp256k1.c
 libsecp256k1_la_CPPFLAGS = -I$(top_srcdir)/include -I$(top_srcdir)/src $(SECP_INCLUDES)
 libsecp256k1_la_LIBADD = $(SECP_LIBS) $(COMMON_LIB) $(PRECOMPUTED_LIB)
-libsecp256k1_la_LDFLAGS = -no-undefined
+libsecp256k1_la_LDFLAGS = -no-undefined -version-info $(LIB_VERSION_CURRENT):$(LIB_VERSION_REVISION):$(LIB_VERSION_AGE)
 
 if VALGRIND_ENABLED
 libsecp256k1_la_CPPFLAGS += -DVALGRIND

configure.ac

@@ -8,6 +8,15 @@ define(_PKG_VERSION_MINOR, 1)
 define(_PKG_VERSION_BUILD, 0)
 define(_PKG_VERSION_IS_RELEASE, false)
 
+# The library version is based on libtool versioning of the ABI. The set of
+# rules for updating the version can be found here:
+# https://www.gnu.org/software/libtool/manual/html_node/Updating-version-info.html
+# All changes in experimental modules are treated as if they don't affect the
+# interface and therefore only increase the revision.
+define(_LIB_VERSION_CURRENT, 0)
+define(_LIB_VERSION_REVISION, 0)
+define(_LIB_VERSION_AGE, 0)
+
 AC_INIT([libsecp256k1],m4_join([.], _PKG_VERSION_MAJOR, _PKG_VERSION_MINOR, _PKG_VERSION_BUILD)m4_if(_PKG_VERSION_IS_RELEASE, [true], [], [-pre]),[https://github.com/bitcoin-core/secp256k1/issues],[libsecp256k1],[https://github.com/bitcoin-core/secp256k1])
 
 AC_CONFIG_AUX_DIR([build-aux])
@@ -391,6 +400,9 @@ AM_CONDITIONAL([ENABLE_MODULE_EXTRAKEYS], [test x"$enable_module_extrakeys" = x"
 AM_CONDITIONAL([ENABLE_MODULE_SCHNORRSIG], [test x"$enable_module_schnorrsig" = x"yes"])
 AM_CONDITIONAL([USE_EXTERNAL_ASM], [test x"$use_external_asm" = x"yes"])
 AM_CONDITIONAL([USE_ASM_ARM], [test x"$set_asm" = x"arm"])
+AC_SUBST(LIB_VERSION_CURRENT, _LIB_VERSION_CURRENT)
+AC_SUBST(LIB_VERSION_REVISION, _LIB_VERSION_REVISION)
+AC_SUBST(LIB_VERSION_AGE, _LIB_VERSION_AGE)
 
 # Make sure nothing new is exported so that we don't break the cache.
 PKGCONFIG_PATH_TEMP="$PKG_CONFIG_PATH"