ref: 009439541d2c6e8af2596f8fb1b4df85861fd212
dir: /third_party/boringssl/src/crypto/compiler_test.cc/
/* Copyright (c) 2017, Google Inc.
*
* Permission to use, copy, modify, and/or distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
* SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
* OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
* CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
#include <limits.h>
#include <stdint.h>
#include <type_traits>
#include <gtest/gtest.h>
#include "test/test_util.h"
// C and C++ have two forms of unspecified behavior: undefined behavior and
// implementation-defined behavior.
//
// Programs that exhibit undefined behavior are invalid. Compilers are
// permitted to, and often do, arbitrarily miscompile them. BoringSSL thus aims
// to avoid undefined behavior.
//
// Implementation-defined behavior is left up to the compiler to define (or
// leave undefined). These are often platform-specific details, such as how big
// |int| is or how |uintN_t| is implemented. Programs that depend on
// implementation-defined behavior are not necessarily invalid, merely less
// portable. A compiler that provides some implementation-defined behavior is
// not permitted to miscompile code that depends on it.
//
// C allows a much wider range of platform behaviors than would be practical
// for us to support, so we make some assumptions on implementation-defined
// behavior. Platforms that violate those assumptions are not supported. This
// file aims to document and test these assumptions, so that platforms outside
// our scope are flagged.
template <typename T>
static void CheckRepresentation(T value) {
SCOPED_TRACE(value);
// Convert to the corresponding two's-complement unsigned value. We use an
// unsigned value so the right-shift below has defined value. Right-shifts of
// negative numbers in C are implementation defined.
//
// If |T| is already unsigned, this is a no-op, as desired.
//
// If |T| is signed, conversion to unsigned is defined to repeatedly add or
// subtract (numerically, not within |T|) one more than the unsigned type's
// maximum value until it fits (this must be a power of two). This is the
// conversion we want.
using UnsignedT = typename std::make_unsigned<T>::type;
UnsignedT value_u = static_cast<UnsignedT>(value);
EXPECT_EQ(sizeof(UnsignedT), sizeof(T));
// Integers must be little-endian.
uint8_t expected[sizeof(UnsignedT)];
for (size_t i = 0; i < sizeof(UnsignedT); i++) {
expected[i] = static_cast<uint8_t>(value_u);
// Divide instead of right-shift to appease compilers that warn if |T| is a
// char. The explicit cast is also needed to appease MSVC if integer
// promotion happened.
value_u = static_cast<UnsignedT>(value_u / 256);
}
EXPECT_EQ(0u, value_u);
// Check that |value| has the expected representation.
EXPECT_EQ(Bytes(expected),
Bytes(reinterpret_cast<const uint8_t *>(&value), sizeof(value)));
}
TEST(CompilerTest, IntegerRepresentation) {
static_assert(CHAR_BIT == 8, "BoringSSL only supports 8-bit chars");
static_assert(UCHAR_MAX == 0xff, "BoringSSL only supports 8-bit chars");
// Require that |unsigned char| and |uint8_t| be the same type. We require
// that type-punning through |uint8_t| is not a strict aliasing violation. In
// principle, type-punning should be done with |memcpy|, which would make this
// moot.
//
// However, C made too many historical mistakes with the types and signedness
// of character strings. As a result, aliasing between all variations on 8-bit
// chars are a practical necessity for all real C code. We do not support
// toolchains that break this assumption.
static_assert(
std::is_same<unsigned char, uint8_t>::value,
"BoringSSL requires uint8_t and unsigned char be the same type");
uint8_t u8 = 0;
unsigned char *ptr = &u8;
(void)ptr;
// Sized integers have the expected size.
static_assert(sizeof(uint8_t) == 1u, "uint8_t has the wrong size");
static_assert(sizeof(uint16_t) == 2u, "uint16_t has the wrong size");
static_assert(sizeof(uint32_t) == 4u, "uint32_t has the wrong size");
static_assert(sizeof(uint64_t) == 8u, "uint64_t has the wrong size");
// size_t does not exceed uint64_t.
static_assert(sizeof(size_t) <= 8u, "size_t must not exceed uint64_t");
// Require that |int| be exactly 32 bits. OpenSSL historically mixed up
// |unsigned| and |uint32_t|, so we require it be at least 32 bits. Requiring
// at most 32-bits is a bit more subtle. C promotes arithemetic operands to
// |int| when they fit. But this means, if |int| is 2N bits wide, multiplying
// two maximum-sized |uintN_t|s is undefined by integer overflow!
//
// We attempt to handle this for |uint16_t|, assuming a 32-bit |int|, but we
// make no attempts to correct for this with |uint32_t| for a 64-bit |int|.
// Thus BoringSSL does not support ILP64 platforms.
//
// This test is on |INT_MAX| and |INT32_MAX| rather than sizeof because it is
// theoretically allowed for sizeof(int) to be 4 but include padding bits.
static_assert(INT_MAX == INT32_MAX, "BoringSSL requires int be 32-bit");
static_assert(UINT_MAX == UINT32_MAX,
"BoringSSL requires unsigned be 32-bit");
CheckRepresentation(static_cast<signed char>(127));
CheckRepresentation(static_cast<signed char>(1));
CheckRepresentation(static_cast<signed char>(0));
CheckRepresentation(static_cast<signed char>(-1));
CheckRepresentation(static_cast<signed char>(-42));
CheckRepresentation(static_cast<signed char>(-128));
CheckRepresentation(static_cast<int>(INT_MAX));
CheckRepresentation(static_cast<int>(0x12345678));
CheckRepresentation(static_cast<int>(1));
CheckRepresentation(static_cast<int>(0));
CheckRepresentation(static_cast<int>(-1));
CheckRepresentation(static_cast<int>(-0x12345678));
CheckRepresentation(static_cast<int>(INT_MIN));
CheckRepresentation(static_cast<unsigned>(UINT_MAX));
CheckRepresentation(static_cast<unsigned>(0x12345678));
CheckRepresentation(static_cast<unsigned>(1));
CheckRepresentation(static_cast<unsigned>(0));
CheckRepresentation(static_cast<long>(LONG_MAX));
CheckRepresentation(static_cast<long>(0x12345678));
CheckRepresentation(static_cast<long>(1));
CheckRepresentation(static_cast<long>(0));
CheckRepresentation(static_cast<long>(-1));
CheckRepresentation(static_cast<long>(-0x12345678));
CheckRepresentation(static_cast<long>(LONG_MIN));
CheckRepresentation(static_cast<unsigned long>(ULONG_MAX));
CheckRepresentation(static_cast<unsigned long>(0x12345678));
CheckRepresentation(static_cast<unsigned long>(1));
CheckRepresentation(static_cast<unsigned long>(0));
CheckRepresentation(static_cast<int16_t>(0x7fff));
CheckRepresentation(static_cast<int16_t>(0x1234));
CheckRepresentation(static_cast<int16_t>(1));
CheckRepresentation(static_cast<int16_t>(0));
CheckRepresentation(static_cast<int16_t>(-1));
CheckRepresentation(static_cast<int16_t>(-0x7fff - 1));
CheckRepresentation(static_cast<uint16_t>(0xffff));
CheckRepresentation(static_cast<uint16_t>(0x1234));
CheckRepresentation(static_cast<uint16_t>(1));
CheckRepresentation(static_cast<uint16_t>(0));
CheckRepresentation(static_cast<int32_t>(0x7fffffff));
CheckRepresentation(static_cast<int32_t>(0x12345678));
CheckRepresentation(static_cast<int32_t>(1));
CheckRepresentation(static_cast<int32_t>(0));
CheckRepresentation(static_cast<int32_t>(-1));
CheckRepresentation(static_cast<int32_t>(-0x7fffffff - 1));
CheckRepresentation(static_cast<uint32_t>(0xffffffff));
CheckRepresentation(static_cast<uint32_t>(0x12345678));
CheckRepresentation(static_cast<uint32_t>(1));
CheckRepresentation(static_cast<uint32_t>(0));
CheckRepresentation(static_cast<int64_t>(0x7fffffffffffffff));
CheckRepresentation(static_cast<int64_t>(0x123456789abcdef0));
CheckRepresentation(static_cast<int64_t>(1));
CheckRepresentation(static_cast<int64_t>(0));
CheckRepresentation(static_cast<int64_t>(-1));
CheckRepresentation(static_cast<int64_t>(-0x7fffffffffffffff - 1));
CheckRepresentation(static_cast<uint64_t>(0xffffffffffffffff));
CheckRepresentation(static_cast<uint64_t>(0x12345678abcdef0));
CheckRepresentation(static_cast<uint64_t>(1));
CheckRepresentation(static_cast<uint64_t>(0));
}
TEST(CompilerTest, PointerRepresentation) {
// Converting pointers to integers and doing arithmetic on those values are
// both defined. Converting those values back into pointers is undefined,
// but, for aliasing checks, we require that the implementation-defined
// result of that computation commutes with pointer arithmetic.
char chars[256];
for (size_t i = 0; i < sizeof(chars); i++) {
EXPECT_EQ(reinterpret_cast<uintptr_t>(chars) + i,
reinterpret_cast<uintptr_t>(chars + i));
}
int ints[256];
for (size_t i = 0; i < OPENSSL_ARRAY_SIZE(ints); i++) {
EXPECT_EQ(reinterpret_cast<uintptr_t>(ints) + i * sizeof(int),
reinterpret_cast<uintptr_t>(ints + i));
}
// nullptr must be represented by all zeros in memory. This is necessary so
// structs may be initialized by memset(0).
int *null = nullptr;
uint8_t bytes[sizeof(null)] = {0};
EXPECT_EQ(Bytes(bytes),
Bytes(reinterpret_cast<uint8_t *>(&null), sizeof(null)));
}