libnftables: export public symbols only

Export public symbols (the library API functions) instead of all symbols in
the library.

This patch introduces the required macros to manage the visibility attributes
(mostly copied from libnftnl.git) and also marks each symbol as exported when
they need to be public. Also, introduce a .map file for proper symbol
versioning.

Previous to this patch, libnftables public symbols were:

% dpkg-gensymbols -q -plibnftables -v0.9.1 -O -esrc/.libs/libnftables.so.1 | wc -l
527

With this patch, libnftables symbols are:

% dpkg-gensymbols -q -plibnftables -v0.9.1 -O -esrc/.libs/libnftables.so.1
libnftables.so.1 libnftables #MINVER#
 nft_ctx_add_include_path@Base 0.9.1
 nft_ctx_buffer_error@Base 0.9.1
 nft_ctx_buffer_output@Base 0.9.1
 nft_ctx_clear_include_paths@Base 0.9.1
 nft_ctx_free@Base 0.9.1
 nft_ctx_get_dry_run@Base 0.9.1
 nft_ctx_get_error_buffer@Base 0.9.1
 nft_ctx_get_output_buffer@Base 0.9.1
 nft_ctx_new@Base 0.9.1
 nft_ctx_output_get_debug@Base 0.9.1
 nft_ctx_output_get_flags@Base 0.9.1
 nft_ctx_output_set_debug@Base 0.9.1
 nft_ctx_output_set_flags@Base 0.9.1
 nft_ctx_set_dry_run@Base 0.9.1
 nft_ctx_set_error@Base 0.9.1
 nft_ctx_set_output@Base 0.9.1
 nft_ctx_unbuffer_error@Base 0.9.1
 nft_ctx_unbuffer_output@Base 0.9.1
 nft_run_cmd_from_buffer@Base 0.9.1
 nft_run_cmd_from_filename@Base 0.9.1

Signed-off-by: Arturo Borrero Gonzalez <arturo@netfilter.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

configure.ac

@@ -44,6 +44,11 @@ fi
 
 AM_PROG_AR
 AM_PROG_LIBTOOL
+LT_INIT
+AM_PROG_CC_C_O
+AC_EXEEXT
+AC_DISABLE_STATIC
+CHECK_GCC_FVISIBILITY
 
 AS_IF([test "x$enable_man_doc" = "xyes"], [
        AC_CHECK_PROG(A2X, [a2x], [a2x], [no])

include/utils.h

@@ -11,6 +11,14 @@
 #include <list.h>
 #include <gmputil.h>
 
+#include "config.h"
+#ifdef HAVE_VISIBILITY_HIDDEN
+#       define __visible        __attribute__((visibility("default")))
+#       define EXPORT_SYMBOL(x) typeof(x) (x) __visible;
+#else
+#       define EXPORT_SYMBOL
+#endif
+
 #define BITS_PER_BYTE	8
 
 #define pr_debug(fmt, arg...) printf(fmt, ##arg)

m4/gcc4_visibility.m4

@@ -0,0 +1,21 @@
+
+# GCC 4.x -fvisibility=hidden
+
+AC_DEFUN([CHECK_GCC_FVISIBILITY], [
+	AC_LANG_PUSH([C])
+	saved_CFLAGS="$CFLAGS"
+	CFLAGS="$saved_CFLAGS -fvisibility=hidden"
+	AC_CACHE_CHECK([whether compiler accepts -fvisibility=hidden],
+	  [ac_cv_fvisibility_hidden], AC_COMPILE_IFELSE(
+		[AC_LANG_SOURCE()],
+		[ac_cv_fvisibility_hidden=yes],
+		[ac_cv_fvisibility_hidden=no]
+	))
+	if test "$ac_cv_fvisibility_hidden" = "yes"; then
+		AC_DEFINE([HAVE_VISIBILITY_HIDDEN], [1],
+			[True if compiler supports -fvisibility=hidden])
+		AC_SUBST([GCC_FVISIBILITY_HIDDEN], [-fvisibility=hidden])
+	fi
+	CFLAGS="$saved_CFLAGS"
+	AC_LANG_POP([C])
+])

src/Makefile.am

@@ -19,7 +19,7 @@ AM_CFLAGS = -Wall								\
 	    -Wdeclaration-after-statement -Wsign-compare -Winit-self		\
 	    -Wformat-nonliteral -Wformat-security -Wmissing-format-attribute	\
 	    -Wcast-align -Wundef -Wbad-function-cast				\
-	    -Waggregate-return -Wunused -Wwrite-strings
+	    -Waggregate-return -Wunused -Wwrite-strings ${GCC_FVISIBILITY_HIDDEN}
 
 
 AM_YFLAGS = -d
@@ -63,7 +63,8 @@ libnftables_la_SOURCES =			\
 		tcpopt.c			\
 		socket.c			\
 		print.c				\
-		libnftables.c
+		libnftables.c			\
+		libnftables.map
 
 # yacc and lex generate dirty code
 noinst_LTLIBRARIES = libparser.la
@@ -77,7 +78,8 @@ libparser_la_CFLAGS = ${AM_CFLAGS} \
 		      -Wno-redundant-decls
 
 libnftables_la_LIBADD = ${LIBMNL_LIBS} ${LIBNFTNL_LIBS} libparser.la
-libnftables_la_LDFLAGS = -version-info ${libnftables_LIBVERSION}
+libnftables_la_LDFLAGS = -version-info ${libnftables_LIBVERSION} \
+			 --version-script=$(srcdir)/libnftables.map
 
 if BUILD_MINIGMP
 noinst_LTLIBRARIES += libminigmp.la

src/libnftables.c

@@ -109,6 +109,7 @@ static void nft_exit(void)
 	mark_table_exit();
 }
 
+EXPORT_SYMBOL(nft_ctx_add_include_path);
 int nft_ctx_add_include_path(struct nft_ctx *ctx, const char *path)
 {
 	char **tmp;
@@ -127,6 +128,7 @@ int nft_ctx_add_include_path(struct nft_ctx *ctx, const char *path)
 	return 0;
 }
 
+EXPORT_SYMBOL(nft_ctx_clear_include_paths);
 void nft_ctx_clear_include_paths(struct nft_ctx *ctx)
 {
 	while (ctx->num_include_paths)
@@ -141,6 +143,7 @@ static void nft_ctx_netlink_init(struct nft_ctx *ctx)
 	ctx->nf_sock = nft_mnl_socket_open();
 }
 
+EXPORT_SYMBOL(nft_ctx_new);
 struct nft_ctx *nft_ctx_new(uint32_t flags)
 {
 	struct nft_ctx *ctx;
@@ -226,21 +229,25 @@ static int exit_cookie(struct cookie *cookie)
 	return 0;
 }
 
+EXPORT_SYMBOL(nft_ctx_buffer_output);
 int nft_ctx_buffer_output(struct nft_ctx *ctx)
 {
 	return init_cookie(&ctx->output.output_cookie);
 }
 
+EXPORT_SYMBOL(nft_ctx_unbuffer_output);
 int nft_ctx_unbuffer_output(struct nft_ctx *ctx)
 {
 	return exit_cookie(&ctx->output.output_cookie);
 }
 
+EXPORT_SYMBOL(nft_ctx_buffer_error);
 int nft_ctx_buffer_error(struct nft_ctx *ctx)
 {
 	return init_cookie(&ctx->output.error_cookie);
 }
 
+EXPORT_SYMBOL(nft_ctx_unbuffer_error);
 int nft_ctx_unbuffer_error(struct nft_ctx *ctx)
 {
 	return exit_cookie(&ctx->output.error_cookie);
@@ -262,16 +269,19 @@ static const char *get_cookie_buffer(struct cookie *cookie)
 	return cookie->buf;
 }
 
+EXPORT_SYMBOL(nft_ctx_get_output_buffer);
 const char *nft_ctx_get_output_buffer(struct nft_ctx *ctx)
 {
 	return get_cookie_buffer(&ctx->output.output_cookie);
 }
 
+EXPORT_SYMBOL(nft_ctx_get_error_buffer);
 const char *nft_ctx_get_error_buffer(struct nft_ctx *ctx)
 {
 	return get_cookie_buffer(&ctx->output.error_cookie);
 }
 
+EXPORT_SYMBOL(nft_ctx_free);
 void nft_ctx_free(struct nft_ctx *ctx)
 {
 	if (ctx->nf_sock)
@@ -287,6 +297,7 @@ void nft_ctx_free(struct nft_ctx *ctx)
 	nft_exit();
 }
 
+EXPORT_SYMBOL(nft_ctx_set_output);
 FILE *nft_ctx_set_output(struct nft_ctx *ctx, FILE *fp)
 {
 	FILE *old = ctx->output.output_fp;
@@ -299,6 +310,7 @@ FILE *nft_ctx_set_output(struct nft_ctx *ctx, FILE *fp)
 	return old;
 }
 
+EXPORT_SYMBOL(nft_ctx_set_error);
 FILE *nft_ctx_set_error(struct nft_ctx *ctx, FILE *fp)
 {
 	FILE *old = ctx->output.error_fp;
@@ -311,30 +323,36 @@ FILE *nft_ctx_set_error(struct nft_ctx *ctx, FILE *fp)
 	return old;
 }
 
+EXPORT_SYMBOL(nft_ctx_get_dry_run);
 bool nft_ctx_get_dry_run(struct nft_ctx *ctx)
 {
 	return ctx->check;
 }
 
+EXPORT_SYMBOL(nft_ctx_set_dry_run);
 void nft_ctx_set_dry_run(struct nft_ctx *ctx, bool dry)
 {
 	ctx->check = dry;
 }
 
+EXPORT_SYMBOL(nft_ctx_output_get_flags);
 unsigned int nft_ctx_output_get_flags(struct nft_ctx *ctx)
 {
 	return ctx->output.flags;
 }
 
+EXPORT_SYMBOL(nft_ctx_output_set_flags);
 void nft_ctx_output_set_flags(struct nft_ctx *ctx, unsigned int flags)
 {
 	ctx->output.flags = flags;
 }
 
+EXPORT_SYMBOL(nft_ctx_output_get_debug);
 unsigned int nft_ctx_output_get_debug(struct nft_ctx *ctx)
 {
 	return ctx->debug_mask;
 }
+EXPORT_SYMBOL(nft_ctx_output_set_debug);
 void nft_ctx_output_set_debug(struct nft_ctx *ctx, unsigned int mask)
 {
 	ctx->debug_mask = mask;
@@ -407,6 +425,7 @@ static int nft_evaluate(struct nft_ctx *nft, struct list_head *msgs,
 	return 0;
 }
 
+EXPORT_SYMBOL(nft_run_cmd_from_buffer);
 int nft_run_cmd_from_buffer(struct nft_ctx *nft, const char *buf)
 {
 	int rc = -EINVAL, parser_rc;
@@ -458,6 +477,7 @@ err:
 	return rc;
 }
 
+EXPORT_SYMBOL(nft_run_cmd_from_filename);
 int nft_run_cmd_from_filename(struct nft_ctx *nft, const char *filename)
 {
 	struct cmd *cmd, *next;

src/libnftables.map

@@ -0,0 +1,25 @@
+LIBNFTABLES_1 {
+global:
+  nft_ctx_add_include_path;
+  nft_ctx_clear_include_pat;
+  nft_ctx_new;
+  nft_ctx_buffer_output;
+  nft_ctx_unbuffer_output;
+  nft_ctx_buffer_error;
+  nft_ctx_unbuffer_error;
+  nft_ctx_get_output_buffer;
+  nft_ctx_get_error_buffer;
+  nft_ctx_free;
+  nft_ctx_set_output;
+  nft_ctx_set_error;
+  nft_ctx_get_dry_run;
+  nft_ctx_set_dry_run;
+  nft_ctx_output_get_flags;
+  nft_ctx_output_set_flags;
+  nft_ctx_output_get_debug;
+  nft_ctx_output_set_debug;
+  nft_run_cmd_from_buffer;
+  nft_run_cmd_from_filename;
+
+local: *;
+};