Merge #799: Add fallback LE/BE for architectures with known endianness + SHA256 selftest

8bc6aef Add SHA256 selftest (Pieter Wuille)
5e5fb28 Use additional system macros to figure out endianness (Pieter Wuille)

Pull request description:

  These are all the architecture macros I could find with known endianness. Use those as a fallback when __BYTE_ORDER__ isn't available.

  See #787 (comment)

  It also adds a SHA256 selftest, so that improperly overriding the endianness detection will be detected at runtime.

ACKs for top commit:
  real-or-random:
    ACK 8bc6aef I read the diff, and tested that the self-test passes/fails with/without the correct endianness setting
  gmaxwell:
    ACK 8bc6aef  looks good and I also ran the tests on MIPS-BE and verified that forcing it to LE makes the runtime test  fail.

Tree-SHA512: aca4cebcd0715dcf5b58f5763cb4283af238987f43bd83a650e38e127f348131692b2eed7ae5b2ae96046d9b971fc77c6ab44467689399fe470a605c3458ecc5

Author: real-or-random

Makefile.am

@@ -38,6 +38,7 @@ noinst_HEADERS += src/assumptions.h
 noinst_HEADERS += src/util.h
 noinst_HEADERS += src/scratch.h
 noinst_HEADERS += src/scratch_impl.h
+noinst_HEADERS += src/selftest.h
 noinst_HEADERS += src/testrand.h
 noinst_HEADERS += src/testrand_impl.h
 noinst_HEADERS += src/hash.h

src/secp256k1.c

@@ -20,6 +20,7 @@
 #include "eckey_impl.h"
 #include "hash_impl.h"
 #include "scratch_impl.h"
+#include "selftest.h"
 
 #if defined(VALGRIND)
 # include <valgrind/memcheck.h>
@@ -118,6 +119,9 @@ secp256k1_context* secp256k1_context_preallocated_create(void* prealloc, unsigne
     size_t prealloc_size;
     secp256k1_context* ret;
 
+    if (!secp256k1_selftest()) {
+        secp256k1_callback_call(&default_error_callback, "self test failed");
+    }
     VERIFY_CHECK(prealloc != NULL);
     prealloc_size = secp256k1_context_preallocated_size(flags);
     ret = (secp256k1_context*)manual_alloc(&prealloc, sizeof(secp256k1_context), base, prealloc_size);

src/selftest.h

@@ -0,0 +1,32 @@
+/**********************************************************************
+ * Copyright (c) 2020 Pieter Wuille                                   *
+ * Distributed under the MIT software license, see the accompanying   *
+ * file COPYING or http://www.opensource.org/licenses/mit-license.php.*
+ **********************************************************************/
+
+#ifndef SECP256K1_SELFTEST_H
+#define SECP256K1_SELFTEST_H
+
+#include "hash.h"
+
+#include <string.h>
+
+static int secp256k1_selftest_sha256(void) {
+    static const char *input63 = "For this sample, this 63-byte string will be used as input data";
+    static const unsigned char output32[32] = {
+        0xf0, 0x8a, 0x78, 0xcb, 0xba, 0xee, 0x08, 0x2b, 0x05, 0x2a, 0xe0, 0x70, 0x8f, 0x32, 0xfa, 0x1e,
+        0x50, 0xc5, 0xc4, 0x21, 0xaa, 0x77, 0x2b, 0xa5, 0xdb, 0xb4, 0x06, 0xa2, 0xea, 0x6b, 0xe3, 0x42,
+    };
+    unsigned char out[32];
+    secp256k1_sha256 hasher;
+    secp256k1_sha256_initialize(&hasher);
+    secp256k1_sha256_write(&hasher, (const unsigned char*)input63, 63);
+    secp256k1_sha256_finalize(&hasher, out);
+    return memcmp(out, output32, 32) == 0;
+}
+
+static int secp256k1_selftest(void) {
+    return secp256k1_selftest_sha256();
+}
+
+#endif /* SECP256K1_SELFTEST_H */

src/util.h

@@ -176,16 +176,27 @@ static SECP256K1_INLINE void *manual_alloc(void** prealloc_ptr, size_t alloc_siz
 # define SECP256K1_GNUC_EXT
 #endif
 
-#if defined(__BYTE_ORDER__)
-# if defined(__ORDER_LITTLE_ENDIAN__) && __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__ && !defined(SECP256K1_LITTLE_ENDIAN)
+/* If SECP256K1_{LITTLE,BIG}_ENDIAN is not explicitly provided, infer from various other system macros. */
+#if !defined(SECP256K1_LITTLE_ENDIAN) && !defined(SECP256K1_BIG_ENDIAN)
+/* Inspired by https://github.com/rofl0r/endianness.h/blob/9853923246b065a3b52d2c43835f3819a62c7199/endianness.h#L52L73 */
+# if (defined(__BYTE_ORDER__) && defined(__ORDER_LITTLE_ENDIAN__) && __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__) || \
+     defined(_X86_) || defined(__x86_64__) || defined(__i386__) || \
+     defined(__i486__) || defined(__i586__) || defined(__i686__) || \
+     defined(__MIPSEL) || defined(_MIPSEL) || defined(MIPSEL) || \
+     defined(__ARMEL__) || defined(__AARCH64EL__) || \
+     (defined(__LITTLE_ENDIAN__) && __LITTLE_ENDIAN__ == 1) || \
+     (defined(_LITTLE_ENDIAN) && _LITTLE_ENDIAN == 1) || \
+     defined(_M_IX86) || defined(_M_AMD64) || defined(_M_ARM) /* MSVC */
 #  define SECP256K1_LITTLE_ENDIAN
-# elif defined(__ORDER_BIG_ENDIAN__) && __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__ && !defined(SECP256K1_BIG_ENDIAN)
+# endif
+# if (defined(__BYTE_ORDER__) && defined(__ORDER_BIG_ENDIAN__) && __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__) || \
+     defined(__MIPSEB) || defined(_MIPSEB) || defined(MIPSEB) || \
+     defined(__MICROBLAZEEB__) || defined(__ARMEB__) || defined(__AARCH64EB__) || \
+     (defined(__BIG_ENDIAN__) && __BIG_ENDIAN__ == 1) || \
+     (defined(_BIG_ENDIAN) && _BIG_ENDIAN == 1)
 #  define SECP256K1_BIG_ENDIAN
 # endif
 #endif
-#if defined(_MSC_VER) && defined(_WIN32) && !defined(SECP256K1_LITTLE_ENDIAN)
-# define SECP256K1_LITTLE_ENDIAN
-#endif
 #if defined(SECP256K1_LITTLE_ENDIAN) == defined(SECP256K1_BIG_ENDIAN)
 # error Please make sure that either SECP256K1_LITTLE_ENDIAN or SECP256K1_BIG_ENDIAN is set, see src/util.h.
 #endif