gcc-plugins: Export symbols needed by gcc

This explicitly exports symbols that gcc expects from plugins.

Based on code from Emese Revfy.
Signed-off-by: Kees Cook <keescook@chromium.org>

scripts/gcc-plugins/cyc_complexity_plugin.c

@@ -20,7 +20,7 @@
 
 #include "gcc-common.h"
 
-int plugin_is_GPL_compatible;
+__visible int plugin_is_GPL_compatible;
 
 static struct plugin_info cyc_complexity_plugin_info = {
 	.version	= "20160225",
@@ -49,7 +49,7 @@ static unsigned int cyc_complexity_execute(void)
 
 #include "gcc-generate-gimple-pass.h"
 
-int plugin_init(struct plugin_name_args *plugin_info, struct plugin_gcc_version *version)
+__visible int plugin_init(struct plugin_name_args *plugin_info, struct plugin_gcc_version *version)
 {
 	const char * const plugin_name = plugin_info->base_name;
 	struct register_pass_info cyc_complexity_pass_info;

scripts/gcc-plugins/gcc-common.h

@@ -130,6 +130,7 @@ extern void dump_gimple_stmt(pretty_printer *, gimple, int, int);
 #endif
 
 #define __unused __attribute__((__unused__))
+#define __visible __attribute__((visibility("default")))
 
 #define DECL_NAME_POINTER(node) IDENTIFIER_POINTER(DECL_NAME(node))
 #define DECL_NAME_LENGTH(node) IDENTIFIER_LENGTH(DECL_NAME(node))

scripts/gcc-plugins/latent_entropy_plugin.c

@@ -77,7 +77,7 @@
 
 #include "gcc-common.h"
 
-int plugin_is_GPL_compatible;
+__visible int plugin_is_GPL_compatible;
 
 static GTY(()) tree latent_entropy_decl;
 
@@ -584,7 +584,7 @@ static void latent_entropy_start_unit(void *gcc_data __unused,
 	| TODO_update_ssa
 #include "gcc-generate-gimple-pass.h"
 
-int plugin_init(struct plugin_name_args *plugin_info,
+__visible int plugin_init(struct plugin_name_args *plugin_info,
 			  struct plugin_gcc_version *version)
 {
 	bool enabled = true;

scripts/gcc-plugins/sancov_plugin.c

@@ -21,7 +21,7 @@
 
 #include "gcc-common.h"
 
-int plugin_is_GPL_compatible;
+__visible int plugin_is_GPL_compatible;
 
 tree sancov_fndecl;
 
@@ -86,7 +86,7 @@ static void sancov_start_unit(void __unused *gcc_data, void __unused *user_data)
 #endif
 }
 
-int plugin_init(struct plugin_name_args *plugin_info, struct plugin_gcc_version *version)
+__visible int plugin_init(struct plugin_name_args *plugin_info, struct plugin_gcc_version *version)
 {
 	int i;
 	struct register_pass_info sancov_plugin_pass_info;