1 /* Copyright (c) 2017, Google Inc.
2 *
3 * Permission to use, copy, modify, and/or distribute this software for any
4 * purpose with or without fee is hereby granted, provided that the above
5 * copyright notice and this permission notice appear in all copies.
6 *
7 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
8 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
9 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
10 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
11 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
12 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
13 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
14
15 #include <limits.h>
16 #include <stdint.h>
17
18 #include <type_traits>
19
20 #include <gtest/gtest.h>
21
22 #include "test/test_util.h"
23
24
25 // C and C++ have two forms of unspecified behavior: undefined behavior and
26 // implementation-defined behavior.
27 //
28 // Programs that exhibit undefined behavior are invalid. Compilers are
29 // permitted to, and often do, arbitrarily miscompile them. BoringSSL thus aims
30 // to avoid undefined behavior.
31 //
32 // Implementation-defined behavior is left up to the compiler to define (or
33 // leave undefined). These are often platform-specific details, such as how big
34 // |int| is or how |uintN_t| is implemented. Programs that depend on
35 // implementation-defined behavior are not necessarily invalid, merely less
36 // portable. A compiler that provides some implementation-defined behavior is
37 // not permitted to miscompile code that depends on it.
38 //
39 // C allows a much wider range of platform behaviors than would be practical
40 // for us to support, so we make some assumptions on implementation-defined
41 // behavior. Platforms that violate those assumptions are not supported. This
42 // file aims to document and test these assumptions, so that platforms outside
43 // our scope are flagged.
44
45 template <typename T>
CheckRepresentation(T value)46 static void CheckRepresentation(T value) {
47 SCOPED_TRACE(value);
48
49 // Convert to the corresponding two's-complement unsigned value. We use an
50 // unsigned value so the right-shift below has defined value. Right-shifts of
51 // negative numbers in C are implementation defined.
52 //
53 // If |T| is already unsigned, this is a no-op, as desired.
54 //
55 // If |T| is signed, conversion to unsigned is defined to repeatedly add or
56 // subtract (numerically, not within |T|) one more than the unsigned type's
57 // maximum value until it fits (this must be a power of two). This is the
58 // conversion we want.
59 using UnsignedT = typename std::make_unsigned<T>::type;
60 UnsignedT value_u = static_cast<UnsignedT>(value);
61 EXPECT_EQ(sizeof(UnsignedT), sizeof(T));
62
63 // Integers must be little-endian.
64 uint8_t expected[sizeof(UnsignedT)];
65 for (size_t i = 0; i < sizeof(UnsignedT); i++) {
66 expected[i] = static_cast<uint8_t>(value_u);
67 // Divide instead of right-shift to appease compilers that warn if |T| is a
68 // char. The explicit cast is also needed to appease MSVC if integer
69 // promotion happened.
70 value_u = static_cast<UnsignedT>(value_u / 256);
71 }
72 EXPECT_EQ(0u, value_u);
73
74 // Check that |value| has the expected representation.
75 EXPECT_EQ(Bytes(expected),
76 Bytes(reinterpret_cast<const uint8_t *>(&value), sizeof(value)));
77 }
78
TEST(CompilerTest,IntegerRepresentation)79 TEST(CompilerTest, IntegerRepresentation) {
80 static_assert(CHAR_BIT == 8, "BoringSSL only supports 8-bit chars");
81 static_assert(UCHAR_MAX == 0xff, "BoringSSL only supports 8-bit chars");
82
83 // Require that |unsigned char| and |uint8_t| be the same type. We require
84 // that type-punning through |uint8_t| is not a strict aliasing violation. In
85 // principle, type-punning should be done with |memcpy|, which would make this
86 // moot.
87 //
88 // However, C made too many historical mistakes with the types and signedness
89 // of character strings. As a result, aliasing between all variations on 8-bit
90 // chars are a practical necessity for all real C code. We do not support
91 // toolchains that break this assumption.
92 static_assert(
93 std::is_same<unsigned char, uint8_t>::value,
94 "BoringSSL requires uint8_t and unsigned char be the same type");
95 uint8_t u8 = 0;
96 unsigned char *ptr = &u8;
97 (void)ptr;
98
99 // Sized integers have the expected size.
100 static_assert(sizeof(uint8_t) == 1u, "uint8_t has the wrong size");
101 static_assert(sizeof(uint16_t) == 2u, "uint16_t has the wrong size");
102 static_assert(sizeof(uint32_t) == 4u, "uint32_t has the wrong size");
103 static_assert(sizeof(uint64_t) == 8u, "uint64_t has the wrong size");
104
105 // size_t does not exceed uint64_t.
106 static_assert(sizeof(size_t) <= 8u, "size_t must not exceed uint64_t");
107
108 // Require that |int| be exactly 32 bits. OpenSSL historically mixed up
109 // |unsigned| and |uint32_t|, so we require it be at least 32 bits. Requiring
110 // at most 32-bits is a bit more subtle. C promotes arithemetic operands to
111 // |int| when they fit. But this means, if |int| is 2N bits wide, multiplying
112 // two maximum-sized |uintN_t|s is undefined by integer overflow!
113 //
114 // We attempt to handle this for |uint16_t|, assuming a 32-bit |int|, but we
115 // make no attempts to correct for this with |uint32_t| for a 64-bit |int|.
116 // Thus BoringSSL does not support ILP64 platforms.
117 //
118 // This test is on |INT_MAX| and |INT32_MAX| rather than sizeof because it is
119 // theoretically allowed for sizeof(int) to be 4 but include padding bits.
120 static_assert(INT_MAX == INT32_MAX, "BoringSSL requires int be 32-bit");
121 static_assert(UINT_MAX == UINT32_MAX,
122 "BoringSSL requires unsigned be 32-bit");
123
124 CheckRepresentation(static_cast<signed char>(127));
125 CheckRepresentation(static_cast<signed char>(1));
126 CheckRepresentation(static_cast<signed char>(0));
127 CheckRepresentation(static_cast<signed char>(-1));
128 CheckRepresentation(static_cast<signed char>(-42));
129 CheckRepresentation(static_cast<signed char>(-128));
130
131 CheckRepresentation(static_cast<int>(INT_MAX));
132 CheckRepresentation(static_cast<int>(0x12345678));
133 CheckRepresentation(static_cast<int>(1));
134 CheckRepresentation(static_cast<int>(0));
135 CheckRepresentation(static_cast<int>(-1));
136 CheckRepresentation(static_cast<int>(-0x12345678));
137 CheckRepresentation(static_cast<int>(INT_MIN));
138
139 CheckRepresentation(static_cast<unsigned>(UINT_MAX));
140 CheckRepresentation(static_cast<unsigned>(0x12345678));
141 CheckRepresentation(static_cast<unsigned>(1));
142 CheckRepresentation(static_cast<unsigned>(0));
143
144 CheckRepresentation(static_cast<long>(LONG_MAX));
145 CheckRepresentation(static_cast<long>(0x12345678));
146 CheckRepresentation(static_cast<long>(1));
147 CheckRepresentation(static_cast<long>(0));
148 CheckRepresentation(static_cast<long>(-1));
149 CheckRepresentation(static_cast<long>(-0x12345678));
150 CheckRepresentation(static_cast<long>(LONG_MIN));
151
152 CheckRepresentation(static_cast<unsigned long>(ULONG_MAX));
153 CheckRepresentation(static_cast<unsigned long>(0x12345678));
154 CheckRepresentation(static_cast<unsigned long>(1));
155 CheckRepresentation(static_cast<unsigned long>(0));
156
157 CheckRepresentation(static_cast<int16_t>(0x7fff));
158 CheckRepresentation(static_cast<int16_t>(0x1234));
159 CheckRepresentation(static_cast<int16_t>(1));
160 CheckRepresentation(static_cast<int16_t>(0));
161 CheckRepresentation(static_cast<int16_t>(-1));
162 CheckRepresentation(static_cast<int16_t>(-0x7fff - 1));
163
164 CheckRepresentation(static_cast<uint16_t>(0xffff));
165 CheckRepresentation(static_cast<uint16_t>(0x1234));
166 CheckRepresentation(static_cast<uint16_t>(1));
167 CheckRepresentation(static_cast<uint16_t>(0));
168
169 CheckRepresentation(static_cast<int32_t>(0x7fffffff));
170 CheckRepresentation(static_cast<int32_t>(0x12345678));
171 CheckRepresentation(static_cast<int32_t>(1));
172 CheckRepresentation(static_cast<int32_t>(0));
173 CheckRepresentation(static_cast<int32_t>(-1));
174 CheckRepresentation(static_cast<int32_t>(-0x7fffffff - 1));
175
176 CheckRepresentation(static_cast<uint32_t>(0xffffffff));
177 CheckRepresentation(static_cast<uint32_t>(0x12345678));
178 CheckRepresentation(static_cast<uint32_t>(1));
179 CheckRepresentation(static_cast<uint32_t>(0));
180
181 CheckRepresentation(static_cast<int64_t>(0x7fffffffffffffff));
182 CheckRepresentation(static_cast<int64_t>(0x123456789abcdef0));
183 CheckRepresentation(static_cast<int64_t>(1));
184 CheckRepresentation(static_cast<int64_t>(0));
185 CheckRepresentation(static_cast<int64_t>(-1));
186 CheckRepresentation(static_cast<int64_t>(-0x7fffffffffffffff - 1));
187
188 CheckRepresentation(static_cast<uint64_t>(0xffffffffffffffff));
189 CheckRepresentation(static_cast<uint64_t>(0x12345678abcdef0));
190 CheckRepresentation(static_cast<uint64_t>(1));
191 CheckRepresentation(static_cast<uint64_t>(0));
192 }
193
TEST(CompilerTest,PointerRepresentation)194 TEST(CompilerTest, PointerRepresentation) {
195 // Converting pointers to integers and doing arithmetic on those values are
196 // both defined. Converting those values back into pointers is undefined,
197 // but, for aliasing checks, we require that the implementation-defined
198 // result of that computation commutes with pointer arithmetic.
199 char chars[256];
200 for (size_t i = 0; i < sizeof(chars); i++) {
201 EXPECT_EQ(reinterpret_cast<uintptr_t>(chars) + i,
202 reinterpret_cast<uintptr_t>(chars + i));
203 }
204
205 int ints[256];
206 for (size_t i = 0; i < OPENSSL_ARRAY_SIZE(ints); i++) {
207 EXPECT_EQ(reinterpret_cast<uintptr_t>(ints) + i * sizeof(int),
208 reinterpret_cast<uintptr_t>(ints + i));
209 }
210
211 // nullptr must be represented by all zeros in memory. This is necessary so
212 // structs may be initialized by memset(0).
213 int *null = nullptr;
214 uint8_t bytes[sizeof(null)] = {0};
215 EXPECT_EQ(Bytes(bytes),
216 Bytes(reinterpret_cast<uint8_t *>(&null), sizeof(null)));
217 }
218