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1/* Make sure that the stackaddr returned by pthread_getattr_np is
2 reachable.
3
4 Copyright (C) 2012-2019 Free Software Foundation, Inc.
5 This file is part of the GNU C Library.
6
7 The GNU C Library is free software; you can redistribute it and/or
8 modify it under the terms of the GNU Lesser General Public
9 License as published by the Free Software Foundation; either
10 version 2.1 of the License, or (at your option) any later version.
11
12 The GNU C Library is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 Lesser General Public License for more details.
16
17 You should have received a copy of the GNU Lesser General Public
18 License along with the GNU C Library; if not, see
19 <http://www.gnu.org/licenses/>. */
20
21#include <stdio.h>
22#include <string.h>
23#include <sys/resource.h>
24#include <sys/param.h>
25#include <pthread.h>
26#include <alloca.h>
27#include <assert.h>
28#include <unistd.h>
29#include <inttypes.h>
30
31/* There is an obscure bug in the kernel due to which RLIMIT_STACK is sometimes
32 returned as unlimited when it is not, which may cause this test to fail.
33 There is also the other case where RLIMIT_STACK is intentionally set as
34 unlimited or very high, which may result in a vma that is too large and again
35 results in a test case failure. To avoid these problems, we cap the stack
36 size to one less than 8M. See the following mailing list threads for more
37 information about this problem:
38 <https://sourceware.org/ml/libc-alpha/2012-06/msg00599.html>
39 <https://sourceware.org/ml/libc-alpha/2012-06/msg00713.html>. */
40#define MAX_STACK_SIZE (8192 * 1024 - 1)
41
42static size_t pagesize;
43
44/* Check if the page in which TARGET lies is accessible. This will segfault
45 if it fails. */
46static volatile char *
47allocate_and_test (char *target)
48{
49 volatile char *mem = (char *) &mem;
50 /* FIXME: mem >= target for _STACK_GROWSUP. */
51 mem = alloca ((size_t) (mem - target));
52
53 *mem = 42;
54 return mem;
55}
56
57static int
58get_self_pthread_attr (const char *id, void **stackaddr, size_t *stacksize)
59{
60 pthread_attr_t attr;
61 int ret;
62 pthread_t me = pthread_self ();
63
64 if ((ret = pthread_getattr_np (me, &attr)) < 0)
65 {
66 printf ("%s: pthread_getattr_np failed: %s\n", id, strerror (ret));
67 return 1;
68 }
69
70 if ((ret = pthread_attr_getstack (&attr, stackaddr, stacksize)) < 0)
71 {
72 printf ("%s: pthread_attr_getstack returned error: %s\n", id,
73 strerror (ret));
74 return 1;
75 }
76
77 return 0;
78}
79
80/* Verify that the stack size returned by pthread_getattr_np is usable when
81 the returned value is subject to rlimit. */
82static int
83check_stack_top (void)
84{
85 struct rlimit stack_limit;
86 void *stackaddr;
87 volatile void *mem;
88 size_t stacksize = 0;
89 int ret;
90 uintptr_t pagemask = ~(pagesize - 1);
91
92 puts ("Verifying that stack top is accessible");
93
94 ret = getrlimit (RLIMIT_STACK, &stack_limit);
95 if (ret)
96 {
97 perror ("getrlimit failed");
98 return 1;
99 }
100
101 printf ("current rlimit_stack is %zu\n", (size_t) stack_limit.rlim_cur);
102
103 if (get_self_pthread_attr ("check_stack_top", &stackaddr, &stacksize))
104 return 1;
105
106 /* Reduce the rlimit to a page less that what is currently being returned
107 (subject to a maximum of MAX_STACK_SIZE) so that we ensure that
108 pthread_getattr_np uses rlimit. The figure is intentionally unaligned so
109 to verify that pthread_getattr_np returns an aligned stacksize that
110 correctly fits into the rlimit. We don't bother about the case where the
111 stack is limited by the vma below it and not by the rlimit because the
112 stacksize returned in that case is computed from the end of that vma and is
113 hence safe. */
114 stack_limit.rlim_cur = MIN (stacksize - pagesize + 1, MAX_STACK_SIZE);
115 printf ("Adjusting RLIMIT_STACK to %zu\n", (size_t) stack_limit.rlim_cur);
116 if ((ret = setrlimit (RLIMIT_STACK, &stack_limit)) < 0)
117 {
118 perror ("setrlimit failed");
119 return 1;
120 }
121
122 if (get_self_pthread_attr ("check_stack_top2", &stackaddr, &stacksize))
123 return 1;
124
125 printf ("Adjusted rlimit: stacksize=%zu, stackaddr=%p\n", stacksize,
126 stackaddr);
127
128 /* A lot of targets tend to write stuff on top of the user stack during
129 context switches, so we cannot possibly safely go up to the very top of
130 stack and test access there. It is however sufficient to simply check if
131 the top page is accessible, so we target our access halfway up the top
132 page. Thanks Chris Metcalf for this idea. */
133 mem = allocate_and_test (stackaddr + pagesize / 2);
134
135 /* Before we celebrate, make sure we actually did test the same page. */
136 if (((uintptr_t) stackaddr & pagemask) != ((uintptr_t) mem & pagemask))
137 {
138 printf ("We successfully wrote into the wrong page.\n"
139 "Expected %#" PRIxPTR ", but got %#" PRIxPTR "\n",
140 (uintptr_t) stackaddr & pagemask, (uintptr_t) mem & pagemask);
141
142 return 1;
143 }
144
145 puts ("Stack top tests done");
146
147 return 0;
148}
149
150/* TODO: Similar check for thread stacks once the thread stack sizes are
151 fixed. */
152static int
153do_test (void)
154{
155 pagesize = sysconf (_SC_PAGESIZE);
156 return check_stack_top ();
157}
158
159
160#define TEST_FUNCTION do_test ()
161#include "../test-skeleton.c"
162

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