nptl/tst-pthread-getattr.c

   1 /* Make sure that the stackaddr returned by pthread_getattr_np is
   2    reachable.
   3
   4    Copyright (C) 2012-2020 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
  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
  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
  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
 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"