Explicitly export public API (#458)

* Explicitly mark public API of Themis

Introduce a new header <themis/themis_api.h> which defines a function
attribute marker THEMIS_API. It is used to explicitly mark API that is
considered public. These functions will be exported from the library.

Themis does not really provide separate public header files so it's not
immediately obvious which functions have to be marked public. We go with
functions visible when including <themis/themis.h>.

Currently we support only UNIX-like systems so we can limit ourselves
to just Clang and GCC. MSVC requires slightly different syntax but we'll
get back to that when we start supporting Windows again.

* Explicitly mark public API of Soter

Just like with Themis, introduce <soter/soter_api.h> with SOTER_API and
mark all public declarations as such.

Note that Soter also has a... complicated story with header files. It's
not apparent which headers are public and which are private. We consider
public those ones included from <soter/soter.h>.

* Export additional private-use API from Soter

Due to historically sloppy export management, many functions in Themis
(as well as in unit-tests) rely on not-so-public API to be available.
Normally you cannot get access to these functions, but you can if you
import <soter/soter_t.h> or some other internal header files.

Introduce a new marker SOTER_PRIVATE_API to distinguish such functions
from normal exports, and mark all of them exported. There are quite a
few of functions, yeah...

Note that while public functions are marked in header files, private
export functions are marked at definition site. This is required because
some of the source files do not actually include corresponding headers.
Plus, this way this definitions are ugly to look at and discourage from
adding new 'private' exports.

* Set default symbol visibility to hidden

Finally, compile all source code with default symbol visibility set to
"hidden". With this only symbols marked with THEMIS_API, SOTER_API, or
SOTER_PRIVATE_API will get exported from libraries. "static" functions
will never be exported, and non-static functions are also not exported
by default unless explicitly marked as public.

* Fix compilation with C++14

DEPRECATED macro expands into [[deprecated]] attribute when compiling
C++14. Make sure this attribute goes before GCC-like __attribute__
specifiers, or else the compiler will not recognize them properly.

Unfortunately, there is no standard equivalent to visibility attributes.
(And I doubt there'll ever be, based on how C++ standards committee
operates.)

* Windows support in API macros

Add [experimental and untested] support for Windows to the API macros.
Note that Windows uses slightly different approach to DLL linkage. Just
like on Linux and macOS, exported functions should be marked on Windows.
However, _imported_ functions should be explicitly marked as well.

Effectively, this means that we should mark exported functions with
 __declspec(dllexport) when compiling DLL object files, but users of
the DLL should see functions marked with __declspec(dllimport).
We achieve that by using a special macro like THEMIS_EXPORT which is
defined only when compling Themis source code, but not when using it.

* Add new headers to Carthage Xcode project

While not strictly required for build, let's add the headers so that
they are visible in Xcode when browsing.

Makefile

@@ -302,6 +302,9 @@ endif
 # strict checks for docs
 #CFLAGS += -Wdocumentation -Wno-error=documentation
 
+# Explicitly list all exports
+CFLAGS += -fvisibility=hidden
+
 # fixing compatibility between x64 0.9.6 and x64 0.10.0
 # https://github.com/cossacklabs/themis/pull/279
 ifeq ($(NO_SCELL_COMPAT),)

Themis.xcodeproj/project.pbxproj

@@ -398,6 +398,8 @@
 		9F4A24C2223A8FA8005CB63A /* smessage.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; name = smessage.h; path = "src/wrappers/themis/Obj-C/objcthemis/smessage.h"; sourceTree = "<group>"; };
 		9F4A24C3223A8FA8005CB63A /* scell_token.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; name = scell_token.h; path = "src/wrappers/themis/Obj-C/objcthemis/scell_token.h"; sourceTree = "<group>"; };
 		9FBD853C223BFB5E009EAEB3 /* openssl.framework */ = {isa = PBXFileReference; lastKnownFileType = wrapper.framework; name = openssl.framework; path = Carthage/Build/iOS/openssl.framework; sourceTree = "<group>"; };
+		9FD4C3522260D41700132A88 /* soter_api.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; name = soter_api.h; path = src/soter/soter_api.h; sourceTree = "<group>"; };
+		9FD4C3532260D43B00132A88 /* themis_api.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; name = themis_api.h; path = src/themis/themis_api.h; sourceTree = "<group>"; };
 /* End PBXFileReference section */
 
 /* Begin PBXFrameworksBuildPhase section */
@@ -443,6 +445,7 @@
 			children = (
 				9F4A23A6223A742F005CB63A /* ed25519 */,
 				9F4A2383223A740E005CB63A /* openssl */,
+				9FD4C3522260D41700132A88 /* soter_api.h */,
 				9F4A2343223A73B0005CB63A /* soter_asym_cipher.h */,
 				9F4A234B223A73B0005CB63A /* soter_asym_ka.h */,
 				9F4A2350223A73B1005CB63A /* soter_asym_sign.h */,
@@ -589,6 +592,7 @@
 				9F4A242D223A74AF005CB63A /* secure_session.h */,
 				9F4A2431223A74AF005CB63A /* sym_enc_message.c */,
 				9F4A242B223A74AF005CB63A /* sym_enc_message.h */,
+				9FD4C3532260D43B00132A88 /* themis_api.h */,
 				9F4A242F223A74AF005CB63A /* themis_error.h */,
 				9F4A2433223A74AF005CB63A /* themis.h */,
 			);

src/soter/boringssl/soter_asym_cipher.c

@@ -20,6 +20,7 @@
 #include <openssl/rsa.h>
 
 #include "soter/boringssl/soter_engine.h"
+#include "soter/soter_api.h"
 #include "soter/soter_rsa_key.h"
 
 #define OAEP_HASH_SIZE 20
@@ -70,6 +71,7 @@ soter_status_t soter_asym_cipher_import_key(soter_asym_cipher_t* asym_cipher_ctx
 
 /* Padding is ignored. We use OAEP by default. Parameter is to support more paddings in the future
  */
+SOTER_PRIVATE_API
 soter_status_t soter_asym_cipher_init(soter_asym_cipher_t* asym_cipher,
                                       const void* key,
                                       const size_t key_length,
@@ -102,6 +104,7 @@ soter_status_t soter_asym_cipher_init(soter_asym_cipher_t* asym_cipher,
     return SOTER_SUCCESS;
 }
 
+SOTER_PRIVATE_API
 soter_status_t soter_asym_cipher_cleanup(soter_asym_cipher_t* asym_cipher)
 {
     if (!asym_cipher) {

src/soter/boringssl/soter_asym_ka.c

@@ -19,6 +19,7 @@
 #include <openssl/ec.h>
 
 #include "soter/boringssl/soter_engine.h"
+#include "soter/soter_api.h"
 #include "soter/soter_ec_key.h"
 
 static int soter_alg_to_curve_nid(soter_asym_ka_alg_t alg)
@@ -31,6 +32,7 @@ static int soter_alg_to_curve_nid(soter_asym_ka_alg_t alg)
     }
 }
 
+SOTER_PRIVATE_API
 soter_status_t soter_asym_ka_init(soter_asym_ka_t* asym_ka_ctx, soter_asym_ka_alg_t alg)
 {
     EVP_PKEY* pkey;
@@ -70,6 +72,7 @@ soter_status_t soter_asym_ka_init(soter_asym_ka_t* asym_ka_ctx, soter_asym_ka_al
     return SOTER_SUCCESS;
 }
 
+SOTER_PRIVATE_API
 soter_status_t soter_asym_ka_cleanup(soter_asym_ka_t* asym_ka_ctx)
 {
     if (!asym_ka_ctx) {

src/soter/boringssl/soter_hash.c

@@ -19,6 +19,7 @@
 #include <openssl/evp.h>
 
 #include "soter/boringssl/soter_engine.h"
+#include "soter/soter_api.h"
 
 static const EVP_MD* soter_algo_to_evp_md(soter_hash_algo_t algo)
 {
@@ -32,6 +33,7 @@ static const EVP_MD* soter_algo_to_evp_md(soter_hash_algo_t algo)
     }
 }
 
+SOTER_PRIVATE_API
 soter_status_t soter_hash_init(soter_hash_ctx_t* hash_ctx, soter_hash_algo_t algo)
 {
     const EVP_MD* md = soter_algo_to_evp_md(algo);

src/soter/ed25519/fe.h

@@ -4,6 +4,8 @@
 /* #include "crypto_int32.h" */
 #include <stdint.h>
 
+#include <soter/soter_api.h>
+
 typedef int32_t crypto_int32;
 typedef int64_t crypto_int64;
 typedef uint32_t crypto_uint32;

src/soter/ed25519/fe_isnonzero.c

@@ -9,6 +9,7 @@ return 0 if f != 0
    |f| bounded by 1.1*2^26,1.1*2^25,1.1*2^26,1.1*2^25,etc.
 */
 
+SOTER_PRIVATE_API
 int crypto_verify_32(const unsigned char *x,const unsigned char *y)
 {
   unsigned int differentbits = 0;
@@ -48,6 +49,7 @@ int crypto_verify_32(const unsigned char *x,const unsigned char *y)
   return (1 & ((differentbits - 1) >> 8)) - 1;
 }
 
+SOTER_PRIVATE_API
 int fe_isnonzero(const fe f)
 {
   static const unsigned char zero[32] = {0};

src/soter/ed25519/fe_neg.c

@@ -10,6 +10,7 @@ h = -f
    |h| bounded by 1.1*2^25,1.1*2^24,1.1*2^25,1.1*2^24,etc.
 */
 
+SOTER_PRIVATE_API
 void fe_neg(fe h,const fe f)
 {
   crypto_int32 f0 = f[0];

src/soter/ed25519/fe_tobytes.c

@@ -25,6 +25,7 @@ Basic claim: q = floor(2^(-255)(h + 19 2^(-25)h9 + 2^(-1))).
   so floor(2^(-255)(h + 19 2^(-25) h9 + 2^(-1))) = q.
 */
 
+SOTER_PRIVATE_API
 void fe_tobytes(unsigned char *s,const fe h)
 {
   crypto_int32 h0 = h[0];

src/soter/ed25519/ge.h

@@ -15,6 +15,8 @@ where d = -121665/121666.
   ge_precomp (Duif): (y+x,y-x,2dxy)
 */
 
+#include <soter/soter_api.h>
+
 #include "fe.h"
 
 typedef struct {

src/soter/ed25519/ge_cmp.c

@@ -18,6 +18,7 @@
 #include <string.h>
 #include <stdint.h>
 
+SOTER_PRIVATE_API
 int ge_cmp(const ge_p3 *a, const ge_p3 *b)
 {
 	unsigned char a_comp[ED25519_GE_LENGTH];

src/soter/ed25519/ge_double_scalarmult.c

@@ -43,6 +43,7 @@ and b = b[0]+256*b[1]+...+256^31 b[31].
 B is the Ed25519 base point (x,4/5) with x positive.
 */
 
+SOTER_PRIVATE_API
 void ge_double_scalarmult_vartime(ge_p2 *r,const unsigned char *a,const ge_p3 *A,const unsigned char *b)
 {
   signed char aslide[256];

src/soter/ed25519/ge_frombytes_no_negate.c

@@ -16,6 +16,7 @@
 
 #include "ge_utils.h"
 
+SOTER_PRIVATE_API
 int ge_frombytes_vartime(ge_p3 *h, const unsigned char *s)
 {
 	int res = ge_frombytes_negate_vartime(h, s);

src/soter/ed25519/ge_p2_to_p3.c

@@ -16,6 +16,7 @@
 
 #include "ge_utils.h"
 
+SOTER_PRIVATE_API
 void ge_p2_to_p3(ge_p3 *r, const ge_p2 *p)
 {
 	if (p != (const ge_p2 *)r)

src/soter/ed25519/ge_p3_sub.c

@@ -16,6 +16,7 @@
 
 #include "ge_utils.h"
 
+SOTER_PRIVATE_API
 void ge_p3_sub(ge_p3 *r, const ge_p3 *p, const ge_p3 *q)
 {
 	ge_cached q_cached;

src/soter/ed25519/ge_p3_tobytes.c

@@ -1,5 +1,6 @@
 #include "ge.h"
 
+SOTER_PRIVATE_API
 void ge_p3_tobytes(unsigned char *s,const ge_p3 *h)
 {
   fe recip;

src/soter/ed25519/ge_scalarmult.c

@@ -16,6 +16,7 @@
 
 #include "ge_utils.h"
 
+SOTER_PRIVATE_API
 void ge_scalarmult_blinded(ge_p3 *r, const unsigned char *a, const ge_p3 *A)
 {
 	unsigned char rnd[32];

src/soter/ed25519/ge_scalarmult_base.c

@@ -61,6 +61,7 @@ B is the Ed25519 base point (x,4/5) with x positive.
   a[31] <= 127
 */
 
+SOTER_PRIVATE_API
 void ge_scalarmult_base(ge_p3 *h,const unsigned char *a)
 {
   signed char e[64];

src/soter/ed25519/ge_tobytes.c

@@ -1,5 +1,6 @@
 #include "ge.h"
 
+SOTER_PRIVATE_API
 void ge_tobytes(unsigned char *s,const ge_p2 *h)
 {
   fe recip;

src/soter/ed25519/ge_utils.h

@@ -19,6 +19,8 @@
 #ifndef GE_UTILS_H
 #define GE_UTILS_H
 
+#include <soter/soter_api.h>
+
 #include "ge.h"
 
 #define ED25519_GE_LENGTH 32

src/soter/ed25519/gen_rand_32.c

@@ -17,13 +17,15 @@
 #include "ge_utils.h"
 #include <soter/soter.h>
 
+SOTER_PRIVATE_API
 void clip_random_32(unsigned char *r)
 {
     r[0] &= 248;
     r[31] &= 63;
     r[31] |= 64;
 }
 
+SOTER_PRIVATE_API
 void generate_random_32(unsigned char *r)
 {
 	soter_status_t res = soter_rand(r, ED25519_GE_LENGTH);

src/soter/ed25519/sc.h

@@ -1,6 +1,8 @@
 #ifndef SC_H
 #define SC_H
 
+#include <soter/soter_api.h>
+
 /*
 The set of scalars is \Z/l
 where l = 2^252 + 27742317777372353535851937790883648493.

src/soter/ed25519/sc_muladd.c

@@ -34,6 +34,7 @@ static crypto_uint64 load_4(const unsigned char *in)
   where l = 2^252 + 27742317777372353535851937790883648493.
 */
 
+SOTER_PRIVATE_API
 void sc_muladd(unsigned char *s,const unsigned char *a,const unsigned char *b,const unsigned char *c)
 {
   crypto_int64 a0 = 2097151 & load_3(a);

src/soter/ed25519/sc_reduce.c

@@ -33,6 +33,7 @@ static crypto_uint64 load_4(const unsigned char *in)
   Overwrites s in place.
 */
 
+SOTER_PRIVATE_API
 void sc_reduce(unsigned char *s)
 {
   crypto_int64 s0 = 2097151 & load_3(s);

src/soter/openssl/soter_asym_cipher.c

@@ -20,6 +20,7 @@
 #include <openssl/rsa.h>
 
 #include "soter/openssl/soter_engine.h"
+#include "soter/soter_api.h"
 #include "soter/soter_rsa_key.h"
 
 /* We use only SHA1 for now */
@@ -71,6 +72,7 @@ soter_status_t soter_asym_cipher_import_key(soter_asym_cipher_t* asym_cipher_ctx
 
 /* Padding is ignored. We use OAEP by default. Parameter is to support more paddings in the future
  */
+SOTER_PRIVATE_API
 soter_status_t soter_asym_cipher_init(soter_asym_cipher_t* asym_cipher,
                                       const void* key,
                                       const size_t key_length,
@@ -106,6 +108,7 @@ soter_status_t soter_asym_cipher_init(soter_asym_cipher_t* asym_cipher,
     return SOTER_SUCCESS;
 }
 
+SOTER_PRIVATE_API
 soter_status_t soter_asym_cipher_cleanup(soter_asym_cipher_t* asym_cipher)
 {
     if (!asym_cipher) {

src/soter/openssl/soter_asym_ka.c

@@ -19,6 +19,7 @@
 #include <openssl/ec.h>
 
 #include "soter/openssl/soter_engine.h"
+#include "soter/soter_api.h"
 #include "soter/soter_ec_key.h"
 
 static int soter_alg_to_curve_nid(soter_asym_ka_alg_t alg)
@@ -31,6 +32,7 @@ static int soter_alg_to_curve_nid(soter_asym_ka_alg_t alg)
     }
 }
 
+SOTER_PRIVATE_API
 soter_status_t soter_asym_ka_init(soter_asym_ka_t* asym_ka_ctx, soter_asym_ka_alg_t alg)
 {
     EVP_PKEY* pkey;
@@ -80,6 +82,7 @@ soter_status_t soter_asym_ka_init(soter_asym_ka_t* asym_ka_ctx, soter_asym_ka_al
     return SOTER_SUCCESS;
 }
 
+SOTER_PRIVATE_API
 soter_status_t soter_asym_ka_cleanup(soter_asym_ka_t* asym_ka_ctx)
 {
     if (!asym_ka_ctx) {

src/soter/openssl/soter_hash.c

@@ -19,6 +19,7 @@
 #include <openssl/evp.h>
 
 #include "soter/openssl/soter_engine.h"
+#include "soter/soter_api.h"
 
 static const EVP_MD* soter_algo_to_evp_md(soter_hash_algo_t algo)
 {
@@ -32,6 +33,7 @@ static const EVP_MD* soter_algo_to_evp_md(soter_hash_algo_t algo)
     }
 }
 
+SOTER_PRIVATE_API
 soter_status_t soter_hash_init(soter_hash_ctx_t* hash_ctx, soter_hash_algo_t algo)
 {
     const EVP_MD* md = soter_algo_to_evp_md(algo);

src/soter/soter.mk

@@ -42,6 +42,8 @@ FMT_CHECK += $(patsubst %,$(OBJ_PATH)/%.fmt_check, $(SOTER_FMT_SRC))
 
 SOTER_STATIC = $(BIN_PATH)/$(LIBSOTER_A) $(SOTER_ENGINE_DEPS)
 
+$(SOTER_OBJ): CFLAGS += -DSOTER_EXPORT
+
 $(BIN_PATH)/$(LIBSOTER_A): CMD = $(AR) rcs $@ $(filter %.o, $^)
 
 $(BIN_PATH)/$(LIBSOTER_A): $(SOTER_OBJ)

src/soter/soter_api.h

@@ -0,0 +1,38 @@
+/*
+ * Copyright (c) 2019 Cossack Labs Limited
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef SOTER_API_H
+#define SOTER_API_H
+
+#if defined(__GNUC__) || defined(__clang__)
+#define SOTER_API __attribute__((visibility("default")))
+#elif defined(_WIN32) || defined(_WIN64) || defined(__CYGWIN__)
+#ifdef SOTER_EXPORT
+#define SOTER_API __declspec(dllexport)
+#else
+#define SOTER_API __declspec(dllimport)
+#endif
+#else
+#define SOTER_API
+#endif
+
+/*
+ * Marks API that needs to be exported for technical reasons, but otherwise
+ * is not intended for user consumption.
+ */
+#define SOTER_PRIVATE_API SOTER_API
+
+#endif /* SOTER_API_H */