Merge bitcoin-core/secp256k1#963: "Schnorrsig API overhaul" fixups

90e8344 ci: Add C++ test (Tim Ruffing)
f698caa Use unsigned char consistently for byte arrays (Tim Ruffing)
b5b8e7b Don't declare constants twice (Tim Ruffing)
769528f Don't use string literals for char arrays without NUL termination (Tim Ruffing)
2cc3cfa Fix -Wmissing-braces warning in clang (Tim Ruffing)

Pull request description:

ACKs for top commit:
  jonasnick:
    ACK 90e8344

Tree-SHA512: c26ba3db7514399c502f6c5c6f6ce6703459d83d831765042e331b051aeee282641197c3ae881c614f51ca714a818c5528410d288aadbd3e92361c1e9c129afe

.cirrus.yml

@@ -320,3 +320,23 @@ task:
     - ./ci/cirrus.sh
   << : *CAT_LOGS
 
+task:
+  name: "C++ -fpermissive"
+  container:
+    dockerfile: ci/linux-debian.Dockerfile
+    cpu: 1
+    memory: 1G
+  env:
+    # ./configure correctly errors out when given CC=g++.
+    # We hack around this by passing CC=g++ only to make.
+    CC: gcc
+    MAKEFLAGS: -j2 CC=g++ CFLAGS=-fpermissive
+    WERROR_CFLAGS:
+    EXPERIMENTAL: yes
+    ECDH: yes
+    RECOVERY: yes
+    SCHNORRSIG: yes
+  << : *MERGE_BASE
+  test_script:
+    - ./ci/cirrus.sh
+  << : *CAT_LOGS

ci/linux-debian.Dockerfile

@@ -13,6 +13,7 @@ RUN apt-get install --no-install-recommends --no-upgrade -y \
         git ca-certificates \
         make automake libtool pkg-config dpkg-dev valgrind qemu-user \
         gcc clang llvm libc6-dbg \
+        g++ \
         gcc-i686-linux-gnu libc6-dev-i386-cross libc6-dbg:i386 libubsan1:i386 libasan5:i386 \
         gcc-s390x-linux-gnu libc6-dev-s390x-cross libc6-dbg:s390x \
         gcc-arm-linux-gnueabihf libc6-dev-armhf-cross libc6-dbg:armhf \

include/secp256k1_schnorrsig.h

@@ -85,7 +85,7 @@ typedef struct {
     void* ndata;
 } secp256k1_schnorrsig_extraparams;
 
-#define SECP256K1_SCHNORRSIG_EXTRAPARAMS_MAGIC "\xda\x6f\xb3\x8c"
+#define SECP256K1_SCHNORRSIG_EXTRAPARAMS_MAGIC { 0xda, 0x6f, 0xb3, 0x8c }
 #define SECP256K1_SCHNORRSIG_EXTRAPARAMS_INIT {\
     SECP256K1_SCHNORRSIG_EXTRAPARAMS_MAGIC,\
     NULL,\

src/ecmult.h

@@ -17,7 +17,6 @@ typedef struct {
     secp256k1_ge_storage (*pre_g_128)[]; /* odd multiples of 2^128*generator */
 } secp256k1_ecmult_context;
 
-static const size_t SECP256K1_ECMULT_CONTEXT_PREALLOCATED_SIZE;
 static void secp256k1_ecmult_context_init(secp256k1_ecmult_context *ctx);
 static void secp256k1_ecmult_context_build(secp256k1_ecmult_context *ctx, void **prealloc);
 static void secp256k1_ecmult_context_finalize_memcpy(secp256k1_ecmult_context *dst, const secp256k1_ecmult_context *src);

src/ecmult_gen.h

@@ -35,7 +35,6 @@ typedef struct {
     secp256k1_gej initial;
 } secp256k1_ecmult_gen_context;
 
-static const size_t SECP256K1_ECMULT_GEN_CONTEXT_PREALLOCATED_SIZE;
 static void secp256k1_ecmult_gen_context_init(secp256k1_ecmult_gen_context* ctx);
 static void secp256k1_ecmult_gen_context_build(secp256k1_ecmult_gen_context* ctx, void **prealloc);
 static void secp256k1_ecmult_gen_context_finalize_memcpy(secp256k1_ecmult_gen_context *dst, const secp256k1_ecmult_gen_context* src);

src/modules/schnorrsig/main_impl.h

@@ -47,6 +47,8 @@ static void secp256k1_nonce_function_bip340_sha256_tagged_aux(secp256k1_sha256 *
  * by using the correct tagged hash function. */
 static const unsigned char bip340_algo[13] = "BIP0340/nonce";
 
+static const unsigned char schnorrsig_extraparams_magic[4] = SECP256K1_SCHNORRSIG_EXTRAPARAMS_MAGIC;
+
 static int nonce_function_bip340(unsigned char *nonce32, const unsigned char *msg, size_t msglen, const unsigned char *key32, const unsigned char *xonly_pk32, const unsigned char *algo, size_t algolen, void *data) {
     secp256k1_sha256 sha;
     unsigned char masked_key[32];
@@ -194,7 +196,7 @@ int secp256k1_schnorrsig_sign_custom(const secp256k1_context* ctx, unsigned char
 
     if (extraparams != NULL) {
         ARG_CHECK(secp256k1_memcmp_var(extraparams->magic,
-                                       SECP256K1_SCHNORRSIG_EXTRAPARAMS_MAGIC,
+                                       schnorrsig_extraparams_magic,
                                        sizeof(extraparams->magic)) == 0);
         noncefp = extraparams->noncefp;
         ndata = extraparams->ndata;

src/modules/schnorrsig/tests_impl.h

@@ -122,7 +122,7 @@ void test_schnorrsig_api(void) {
     secp256k1_xonly_pubkey zero_pk;
     unsigned char sig[64];
     secp256k1_schnorrsig_extraparams extraparams = SECP256K1_SCHNORRSIG_EXTRAPARAMS_INIT;
-    secp256k1_schnorrsig_extraparams invalid_extraparams = { 0 };
+    secp256k1_schnorrsig_extraparams invalid_extraparams = {{ 0 }, NULL, NULL};
 
     /** setup **/
     secp256k1_context *none = secp256k1_context_create(SECP256K1_CONTEXT_NONE);
@@ -219,7 +219,7 @@ void test_schnorrsig_api(void) {
 /* Checks that hash initialized by secp256k1_schnorrsig_sha256_tagged has the
  * expected state. */
 void test_schnorrsig_sha256_tagged(void) {
-    char tag[17] = "BIP0340/challenge";
+    unsigned char tag[17] = "BIP0340/challenge";
     secp256k1_sha256 sha;
     secp256k1_sha256 sha_optimized;