Introduce SECP256K1_LOCAL_VAR macro

This change makes the `-fvisibility=hidden` compiler option unnecessary.

Author: hebasto

Makefile.am

@@ -47,6 +47,7 @@ noinst_HEADERS += src/assumptions.h
 noinst_HEADERS += src/checkmem.h
 noinst_HEADERS += src/testutil.h
 noinst_HEADERS += src/util.h
+noinst_HEADERS += src/util_local_visibility.h
 noinst_HEADERS += src/int128.h
 noinst_HEADERS += src/int128_impl.h
 noinst_HEADERS += src/int128_native.h

src/precomputed_ecmult.h

@@ -13,6 +13,8 @@ extern "C" {
 
 #include "ecmult.h"
 #include "group.h"
+#include "util_local_visibility.h"
+
 #if defined(EXHAUSTIVE_TEST_ORDER)
 #    if EXHAUSTIVE_TEST_ORDER == 7
 #        define WINDOW_G 3
@@ -27,8 +29,8 @@ static secp256k1_ge_storage secp256k1_pre_g[ECMULT_TABLE_SIZE(WINDOW_G)];
 static secp256k1_ge_storage secp256k1_pre_g_128[ECMULT_TABLE_SIZE(WINDOW_G)];
 #else /* !defined(EXHAUSTIVE_TEST_ORDER) */
 #    define WINDOW_G ECMULT_WINDOW_SIZE
-extern const secp256k1_ge_storage secp256k1_pre_g[ECMULT_TABLE_SIZE(WINDOW_G)];
-extern const secp256k1_ge_storage secp256k1_pre_g_128[ECMULT_TABLE_SIZE(WINDOW_G)];
+SECP256K1_LOCAL_VAR const secp256k1_ge_storage secp256k1_pre_g[ECMULT_TABLE_SIZE(WINDOW_G)];
+SECP256K1_LOCAL_VAR const secp256k1_ge_storage secp256k1_pre_g_128[ECMULT_TABLE_SIZE(WINDOW_G)];
 #endif /* defined(EXHAUSTIVE_TEST_ORDER) */
 
 #ifdef __cplusplus

src/precomputed_ecmult_gen.h

@@ -13,10 +13,12 @@ extern "C" {
 
 #include "group.h"
 #include "ecmult_gen.h"
+#include "util_local_visibility.h"
+
 #ifdef EXHAUSTIVE_TEST_ORDER
 static secp256k1_ge_storage secp256k1_ecmult_gen_prec_table[COMB_BLOCKS][COMB_POINTS];
 #else
-extern const secp256k1_ge_storage secp256k1_ecmult_gen_prec_table[COMB_BLOCKS][COMB_POINTS];
+SECP256K1_LOCAL_VAR const secp256k1_ge_storage secp256k1_ecmult_gen_prec_table[COMB_BLOCKS][COMB_POINTS];
 #endif /* defined(EXHAUSTIVE_TEST_ORDER) */
 
 #ifdef __cplusplus

src/util_local_visibility.h

@@ -0,0 +1,12 @@
+#ifndef SECP256K1_LOCAL_VISIBILITY_H
+#define SECP256K1_LOCAL_VISIBILITY_H
+
+/* Global variable visibility */
+/* See: https://github.com/bitcoin-core/secp256k1/issues/1181 */
+#if !defined(_WIN32) && defined(__GNUC__) && (__GNUC__ >= 4)
+# define SECP256K1_LOCAL_VAR extern __attribute__ ((visibility ("hidden")))
+#else
+# define SECP256K1_LOCAL_VAR extern
+#endif
+
+#endif /* SECP256K1_LOCAL_VISIBILITY_H */