1 /* Make sure that the stackaddr returned by pthread_getattr_np is
2 reachable.
3
4 Copyright (C) 2012-2021 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 <https://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
42 static size_t pagesize;
43
44 /* Test that the page in which TARGET lies is accessible. This will
45 segfault if the write fails. This function has only half a page
46 of thread stack left and so should not do anything and immediately
47 return the address to which the stack reached. */
48 static volatile uintptr_t
allocate_and_test(char * target)49 allocate_and_test (char *target)
50 {
51 volatile char *mem = (char *) &mem;
52 /* FIXME: mem >= target for _STACK_GROWSUP. */
53 mem = alloca ((size_t) (mem - target));
54
55 *mem = 42;
56 return (uintptr_t) mem;
57 }
58
59 static int
get_self_pthread_attr(const char * id,void ** stackaddr,size_t * stacksize)60 get_self_pthread_attr (const char *id, void **stackaddr, size_t *stacksize)
61 {
62 pthread_attr_t attr;
63 int ret;
64 pthread_t me = pthread_self ();
65
66 if ((ret = pthread_getattr_np (me, &attr)) < 0)
67 {
68 printf ("%s: pthread_getattr_np failed: %s\n", id, strerror (ret));
69 return 1;
70 }
71
72 if ((ret = pthread_attr_getstack (&attr, stackaddr, stacksize)) < 0)
73 {
74 printf ("%s: pthread_attr_getstack returned error: %s\n", id,
75 strerror (ret));
76 return 1;
77 }
78
79 return 0;
80 }
81
82 /* Verify that the stack size returned by pthread_getattr_np is usable when
83 the returned value is subject to rlimit. */
84 static int
check_stack_top(void)85 check_stack_top (void)
86 {
87 struct rlimit stack_limit;
88 void *stackaddr;
89 size_t stacksize = 0;
90 int ret;
91 uintptr_t pagemask = ~(pagesize - 1);
92
93 puts ("Verifying that stack top is accessible");
94
95 ret = getrlimit (RLIMIT_STACK, &stack_limit);
96 if (ret)
97 {
98 perror ("getrlimit failed");
99 return 1;
100 }
101
102 printf ("current rlimit_stack is %zu\n", (size_t) stack_limit.rlim_cur);
103
104 if (get_self_pthread_attr ("check_stack_top", &stackaddr, &stacksize))
105 return 1;
106
107 /* Reduce the rlimit to a page less that what is currently being returned
108 (subject to a maximum of MAX_STACK_SIZE) so that we ensure that
109 pthread_getattr_np uses rlimit. The figure is intentionally unaligned so
110 to verify that pthread_getattr_np returns an aligned stacksize that
111 correctly fits into the rlimit. We don't bother about the case where the
112 stack is limited by the vma below it and not by the rlimit because the
113 stacksize returned in that case is computed from the end of that vma and is
114 hence safe. */
115 stack_limit.rlim_cur = MIN (stacksize - pagesize + 1, MAX_STACK_SIZE);
116 printf ("Adjusting RLIMIT_STACK to %zu\n", (size_t) stack_limit.rlim_cur);
117 if ((ret = setrlimit (RLIMIT_STACK, &stack_limit)) < 0)
118 {
119 perror ("setrlimit failed");
120 return 1;
121 }
122
123 if (get_self_pthread_attr ("check_stack_top2", &stackaddr, &stacksize))
124 return 1;
125
126 printf ("Adjusted rlimit: stacksize=%zu, stackaddr=%p\n", stacksize,
127 stackaddr);
128
129 /* A lot of targets tend to write stuff on top of the user stack during
130 context switches, so we cannot possibly safely go up to the very top of
131 stack and test access there. It is however sufficient to simply check if
132 the top page is accessible, so we target our access halfway up the top
133 page. Thanks Chris Metcalf for this idea. */
134 uintptr_t mem = allocate_and_test (stackaddr + pagesize / 2);
135
136 /* Before we celebrate, make sure we actually did test the same page. */
137 if (((uintptr_t) stackaddr & pagemask) != (mem & pagemask))
138 {
139 printf ("We successfully wrote into the wrong page.\n"
140 "Expected %#" PRIxPTR ", but got %#" PRIxPTR "\n",
141 (uintptr_t) stackaddr & pagemask, mem & pagemask);
142
143 return 1;
144 }
145
146 puts ("Stack top tests done");
147
148 return 0;
149 }
150
151 /* TODO: Similar check for thread stacks once the thread stack sizes are
152 fixed. */
153 static int
do_test(void)154 do_test (void)
155 {
156 pagesize = sysconf (_SC_PAGESIZE);
157 return check_stack_top ();
158 }
159
160
161 #define TEST_FUNCTION do_test ()
162 #include "../test-skeleton.c"
163