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ea1bd74d | 1 | /* Test that explicit_bzero block clears are not optimized out. |
bfff8b1b | 2 | Copyright (C) 2016-2017 Free Software Foundation, Inc. |
ea1bd74d ZW |
3 | This file is part of the GNU C Library. |
4 | ||
5 | The GNU C Library is free software; you can redistribute it and/or | |
6 | modify it under the terms of the GNU Lesser General Public | |
7 | License as published by the Free Software Foundation; either | |
8 | version 2.1 of the License, or (at your option) any later version. | |
9 | ||
10 | The GNU C Library is distributed in the hope that it will be useful, | |
11 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
13 | Lesser General Public License for more details. | |
14 | ||
15 | You should have received a copy of the GNU Lesser General Public | |
16 | License along with the GNU C Library; if not, see | |
17 | <http://www.gnu.org/licenses/>. */ | |
18 | ||
19 | /* This test is conceptually based on a test designed by Matthew | |
20 | Dempsky for the OpenBSD regression suite: | |
21 | <openbsd>/src/regress/lib/libc/explicit_bzero/explicit_bzero.c. | |
22 | The basic idea is, we have a function that contains a | |
23 | block-clearing operation (not necessarily explicit_bzero), after | |
24 | which the block is dead, in the compiler-jargon sense. Execute | |
25 | that function while running on a user-allocated alternative | |
26 | stack. Then we have another pointer to the memory region affected | |
27 | by the block clear -- namely, the original allocation for the | |
28 | alternative stack -- and can find out whether it actually happened. | |
29 | ||
30 | The OpenBSD test uses sigaltstack and SIGUSR1 to get onto an | |
31 | alternative stack. This causes a number of awkward problems; some | |
32 | operating systems (e.g. Solaris and OSX) wipe the signal stack upon | |
33 | returning to the normal stack, there's no way to be sure that other | |
34 | processes running on the same system will not interfere, and the | |
35 | signal stack is very small so it's not safe to call printf there. | |
36 | This implementation instead uses the <ucontext.h> coroutine | |
37 | interface. The coroutine stack is still too small to safely use | |
38 | printf, but we know the OS won't erase it, so we can do all the | |
39 | checks and printing from the normal stack. */ | |
40 | ||
41 | #define _GNU_SOURCE 1 | |
42 | ||
43 | #include <errno.h> | |
44 | #include <signal.h> | |
45 | #include <stdio.h> | |
46 | #include <stdlib.h> | |
47 | #include <string.h> | |
48 | #include <ucontext.h> | |
49 | #include <unistd.h> | |
50 | ||
51 | /* A byte pattern that is unlikely to occur by chance: the first 16 | |
52 | prime numbers (OEIS A000040). */ | |
53 | static const unsigned char test_pattern[16] = | |
54 | { | |
55 | 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53 | |
56 | }; | |
57 | ||
58 | /* Immediately after each subtest returns, we call swapcontext to get | |
59 | back onto the main stack. That call might itself overwrite the | |
60 | test pattern, so we fill a modest-sized buffer with copies of it | |
61 | and check whether any of them survived. */ | |
62 | ||
63 | #define PATTERN_SIZE (sizeof test_pattern) | |
64 | #define PATTERN_REPS 32 | |
65 | #define TEST_BUFFER_SIZE (PATTERN_SIZE * PATTERN_REPS) | |
66 | ||
67 | /* There are three subtests, two of which are sanity checks. | |
68 | Each test follows this sequence: | |
69 | ||
70 | main coroutine | |
71 | ---- -------- | |
72 | advance cur_subtest | |
73 | swap | |
74 | call setup function | |
75 | prepare test buffer | |
76 | swap | |
77 | verify that buffer | |
78 | was filled in | |
79 | swap | |
80 | possibly clear buffer | |
81 | return | |
82 | swap | |
83 | check buffer again, | |
84 | according to test | |
85 | expectation | |
86 | ||
87 | In the "no_clear" case, we don't do anything to the test buffer | |
88 | between preparing it and letting it go out of scope, and we expect | |
89 | to find it. This confirms that the test buffer does get filled in | |
90 | and we can find it from the stack buffer. In the "ordinary_clear" | |
8d71242e FW |
91 | case, we clear it using memset. Depending on the target, the |
92 | compiler may not be able to apply dead store elimination to the | |
93 | memset call, so the test does not fail if the memset is not | |
94 | eliminated. Finally, the "explicit_clear" case uses explicit_bzero | |
95 | and expects _not_ to find the test buffer, which is the real | |
96 | test. */ | |
ea1bd74d ZW |
97 | |
98 | static ucontext_t uc_main, uc_co; | |
99 | ||
100 | /* Always check the test buffer immediately after filling it; this | |
101 | makes externally visible side effects depend on the buffer existing | |
102 | and having been filled in. */ | |
8d71242e | 103 | static inline __attribute__ ((always_inline)) void |
ea1bd74d ZW |
104 | prepare_test_buffer (unsigned char *buf) |
105 | { | |
106 | for (unsigned int i = 0; i < PATTERN_REPS; i++) | |
107 | memcpy (buf + i*PATTERN_SIZE, test_pattern, PATTERN_SIZE); | |
108 | ||
109 | if (swapcontext (&uc_co, &uc_main)) | |
110 | abort (); | |
111 | } | |
112 | ||
113 | static void | |
114 | setup_no_clear (void) | |
115 | { | |
116 | unsigned char buf[TEST_BUFFER_SIZE]; | |
117 | prepare_test_buffer (buf); | |
118 | } | |
119 | ||
120 | static void | |
121 | setup_ordinary_clear (void) | |
122 | { | |
123 | unsigned char buf[TEST_BUFFER_SIZE]; | |
124 | prepare_test_buffer (buf); | |
125 | memset (buf, 0, TEST_BUFFER_SIZE); | |
126 | } | |
127 | ||
128 | static void | |
129 | setup_explicit_clear (void) | |
130 | { | |
131 | unsigned char buf[TEST_BUFFER_SIZE]; | |
132 | prepare_test_buffer (buf); | |
133 | explicit_bzero (buf, TEST_BUFFER_SIZE); | |
134 | } | |
135 | ||
8d71242e FW |
136 | enum test_expectation |
137 | { | |
138 | EXPECT_NONE, EXPECT_SOME, EXPECT_ALL, NO_EXPECTATIONS | |
139 | }; | |
ea1bd74d ZW |
140 | struct subtest |
141 | { | |
142 | void (*setup_subtest) (void); | |
143 | const char *label; | |
144 | enum test_expectation expected; | |
145 | }; | |
146 | static const struct subtest *cur_subtest; | |
147 | ||
148 | static const struct subtest subtests[] = | |
149 | { | |
150 | { setup_no_clear, "no clear", EXPECT_SOME }, | |
8d71242e FW |
151 | /* The memset may happen or not, depending on compiler |
152 | optimizations. */ | |
153 | { setup_ordinary_clear, "ordinary clear", NO_EXPECTATIONS }, | |
ea1bd74d ZW |
154 | { setup_explicit_clear, "explicit clear", EXPECT_NONE }, |
155 | { 0, 0, -1 } | |
156 | }; | |
157 | ||
158 | static void | |
159 | test_coroutine (void) | |
160 | { | |
161 | while (cur_subtest->setup_subtest) | |
162 | { | |
163 | cur_subtest->setup_subtest (); | |
164 | if (swapcontext (&uc_co, &uc_main)) | |
165 | abort (); | |
166 | } | |
167 | } | |
168 | ||
169 | /* All the code above this point runs on the coroutine stack. | |
170 | All the code below this point runs on the main stack. */ | |
171 | ||
172 | static int test_status; | |
173 | static unsigned char *co_stack_buffer; | |
174 | static size_t co_stack_size; | |
175 | ||
176 | static unsigned int | |
177 | count_test_patterns (unsigned char *buf, size_t bufsiz) | |
178 | { | |
179 | unsigned char *first = memmem (buf, bufsiz, test_pattern, PATTERN_SIZE); | |
180 | if (!first) | |
181 | return 0; | |
182 | unsigned int cnt = 0; | |
183 | for (unsigned int i = 0; i < PATTERN_REPS; i++) | |
184 | { | |
185 | unsigned char *p = first + i*PATTERN_SIZE; | |
186 | if (p + PATTERN_SIZE - buf > bufsiz) | |
187 | break; | |
188 | if (memcmp (p, test_pattern, PATTERN_SIZE) == 0) | |
189 | cnt++; | |
190 | } | |
191 | return cnt; | |
192 | } | |
193 | ||
194 | static void | |
195 | check_test_buffer (enum test_expectation expected, | |
196 | const char *label, const char *stage) | |
197 | { | |
198 | unsigned int cnt = count_test_patterns (co_stack_buffer, co_stack_size); | |
199 | switch (expected) | |
200 | { | |
201 | case EXPECT_NONE: | |
202 | if (cnt == 0) | |
203 | printf ("PASS: %s/%s: expected 0 got %d\n", label, stage, cnt); | |
204 | else | |
205 | { | |
206 | printf ("FAIL: %s/%s: expected 0 got %d\n", label, stage, cnt); | |
207 | test_status = 1; | |
208 | } | |
209 | break; | |
210 | ||
211 | case EXPECT_SOME: | |
212 | if (cnt > 0) | |
213 | printf ("PASS: %s/%s: expected some got %d\n", label, stage, cnt); | |
214 | else | |
215 | { | |
216 | printf ("FAIL: %s/%s: expected some got 0\n", label, stage); | |
217 | test_status = 1; | |
218 | } | |
219 | break; | |
220 | ||
221 | case EXPECT_ALL: | |
222 | if (cnt == PATTERN_REPS) | |
223 | printf ("PASS: %s/%s: expected %d got %d\n", label, stage, | |
224 | PATTERN_REPS, cnt); | |
225 | else | |
226 | { | |
227 | printf ("FAIL: %s/%s: expected %d got %d\n", label, stage, | |
228 | PATTERN_REPS, cnt); | |
229 | test_status = 1; | |
230 | } | |
231 | break; | |
232 | ||
8d71242e FW |
233 | case NO_EXPECTATIONS: |
234 | printf ("INFO: %s/%s: found %d patterns%s\n", label, stage, cnt, | |
235 | cnt == 0 ? " (memset not eliminated)" : ""); | |
236 | break; | |
237 | ||
ea1bd74d ZW |
238 | default: |
239 | printf ("ERROR: %s/%s: invalid value for 'expected' = %d\n", | |
240 | label, stage, (int)expected); | |
241 | test_status = 1; | |
242 | } | |
243 | } | |
244 | ||
245 | static void | |
246 | test_loop (void) | |
247 | { | |
248 | cur_subtest = subtests; | |
249 | while (cur_subtest->setup_subtest) | |
250 | { | |
251 | if (swapcontext (&uc_main, &uc_co)) | |
252 | abort (); | |
253 | check_test_buffer (EXPECT_ALL, cur_subtest->label, "prepare"); | |
254 | if (swapcontext (&uc_main, &uc_co)) | |
255 | abort (); | |
256 | check_test_buffer (cur_subtest->expected, cur_subtest->label, "test"); | |
257 | cur_subtest++; | |
258 | } | |
259 | /* Terminate the coroutine. */ | |
260 | if (swapcontext (&uc_main, &uc_co)) | |
261 | abort (); | |
262 | } | |
263 | ||
264 | int | |
265 | do_test (void) | |
266 | { | |
267 | size_t page_alignment = sysconf (_SC_PAGESIZE); | |
268 | if (page_alignment < sizeof (void *)) | |
269 | page_alignment = sizeof (void *); | |
270 | ||
271 | co_stack_size = SIGSTKSZ + TEST_BUFFER_SIZE; | |
272 | if (co_stack_size < page_alignment * 4) | |
273 | co_stack_size = page_alignment * 4; | |
274 | ||
275 | void *p; | |
276 | int err = posix_memalign (&p, page_alignment, co_stack_size); | |
277 | if (err || !p) | |
278 | { | |
279 | printf ("ERROR: allocating alt stack: %s\n", strerror (err)); | |
280 | return 2; | |
281 | } | |
282 | co_stack_buffer = p; | |
283 | ||
284 | if (getcontext (&uc_co)) | |
285 | { | |
286 | printf ("ERROR: allocating coroutine context: %s\n", strerror (err)); | |
287 | return 2; | |
288 | } | |
289 | uc_co.uc_stack.ss_sp = co_stack_buffer; | |
290 | uc_co.uc_stack.ss_size = co_stack_size; | |
291 | uc_co.uc_link = &uc_main; | |
292 | makecontext (&uc_co, test_coroutine, 0); | |
293 | ||
294 | test_loop (); | |
295 | return test_status; | |
296 | } | |
297 | ||
298 | #include <support/test-driver.c> |