about summary refs log tree commit diff
path: root/malloc/tst-free-errno.c
blob: 55c5863dd58d6c1460cea96a4f304d001f9c0874 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
/* Test that free preserves errno.
   Copyright (C) 2020-2023 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

#include <errno.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdint.h>
#include <string.h>
#include <sys/mman.h>
#include <support/check.h>
#include <support/support.h>
#include <support/temp_file.h>
#include <support/xunistd.h>

/* The __attribute__ ((weak)) prevents a GCC optimization.  Without
   it, GCC would "know" that errno is unchanged by calling free (ptr),
   when ptr was the result of a malloc call in the same function.  */
int __attribute__ ((weak))
get_errno (void)
{
  return errno;
}

static int
do_test (void)
{
  /* Check that free() preserves errno.  */
  {
    errno = 1789; /* Liberté, égalité, fraternité.  */
    free (NULL);
    TEST_VERIFY (get_errno () == 1789);
  }
  { /* Large memory allocations, to force mmap.  */
    enum { N = 2 };
    void * volatile ptrs[N];
    size_t i;
    for (i = 0; i < N; i++)
      ptrs[i] = xmalloc (5318153);
    for (i = 0; i < N; i++)
      {
        errno = 1789;
        free (ptrs[i]);
        TEST_VERIFY (get_errno () == 1789);
      }
  }

  /* Test a less common code path.
     When malloc() is based on mmap(), free() can sometimes call munmap().
     munmap() usually succeeds, but fails in a particular situation: when
       - it has to unmap the middle part of a VMA, and
       - the number of VMAs of a process is limited and the limit is
         already reached.
     The latter condition is fulfilled on Linux, when the file
     /proc/sys/vm/max_map_count exists.  For all known Linux versions
     the default limit is at most 65536.
   */
  #if defined __linux__
  if (xopen ("/proc/sys/vm/max_map_count", O_RDONLY, 0) >= 0)
    {
      /* Preparations.  */
      size_t pagesize = getpagesize ();
      void *firstpage_backup = xmalloc (pagesize);
      void *lastpage_backup = xmalloc (pagesize);
      /* Allocate a large memory area, as a bumper, so that the MAP_FIXED
         allocation later will not overwrite parts of the memory areas
         allocated to ld.so or libc.so.  */
      xmmap (NULL, 0x1000000, PROT_READ, MAP_ANONYMOUS | MAP_PRIVATE, -1);
      /* A file descriptor pointing to a regular file.  */
      int fd = create_temp_file ("tst-free-errno", NULL);
      if (fd < 0)
	FAIL_EXIT1 ("cannot create temporary file");

      /* Do a large memory allocation.  */
      size_t big_size = 0x1000000;
      void * volatile ptr = xmalloc (big_size - 0x100);
      char *ptr_aligned = (char *) ((uintptr_t) ptr & ~(pagesize - 1));
      /* This large memory allocation allocated a memory area
	 from ptr_aligned to ptr_aligned + big_size.
	 Enlarge this memory area by adding a page before and a page
	 after it.  */
      memcpy (firstpage_backup, ptr_aligned, pagesize);
      memcpy (lastpage_backup, ptr_aligned + big_size - pagesize,
	      pagesize);
      xmmap (ptr_aligned - pagesize, pagesize + big_size + pagesize,
	     PROT_READ | PROT_WRITE,
	     MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED, -1);
      memcpy (ptr_aligned, firstpage_backup, pagesize);
      memcpy (ptr_aligned + big_size - pagesize, lastpage_backup,
	      pagesize);

      /* Now add as many mappings as we can.
	 Stop at 65536, in order not to crash the machine (in case the
	 limit has been increased by the system administrator).  */
      for (int i = 0; i < 65536; i++)
	if (mmap (NULL, pagesize, PROT_READ, MAP_FILE | MAP_PRIVATE, fd, 0)
	    == MAP_FAILED)
	  break;
      /* Now the number of VMAs of this process has hopefully attained
	 its limit.  */

      errno = 1789;
      /* This call to free() is supposed to call
	   munmap (ptr_aligned, big_size);
	 which increases the number of VMAs by 1, which is supposed
	 to fail.  */
      free (ptr);
      TEST_VERIFY (get_errno () == 1789);
    }
  #endif

  return 0;
}

#include <support/test-driver.c>