lib/c-stack.c

   1 /* Stack overflow handling.
   2
   3    Copyright (C) 2002, 2004, 2006, 2008-2024 Free Software Foundation, Inc.
   4
   5    This program is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation, either version 3 of the License, or
   8    (at your option) any later version.
   9
  10    This program 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
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  17
  18 /* Written by Paul Eggert.  */
  19
  20 /* NOTES:
  21
  22    A program that uses alloca, dynamic arrays, or large local
  23    variables may extend the stack by more than a page at a time.  If
  24    so, when the stack overflows the operating system may not detect
  25    the overflow until the program uses the array, and this module may
  26    incorrectly report a program error instead of a stack overflow.
  27
  28    To avoid this problem, allocate only small objects on the stack; a
  29    program should be OK if it limits single allocations to a page or
  30    less.  Allocate larger arrays in static storage, or on the heap
  31    (e.g., with malloc).  Yes, this is a pain, but we don't know of any
  32    better solution that is portable.
  33
  34    No attempt has been made to deal with multithreaded applications.  */
  35
  36 #include <config.h>
  37
  38 #include "c-stack.h"
  39
  40 #include <errno.h>
  41 #include <inttypes.h>
  42 #include <signal.h>
  43 #include <stddef.h>
  44 #include <stdlib.h>
  45 #include <string.h>
  46 #include <unistd.h>
  47
  48 #if DEBUG
  49 # include <stdio.h>
  50 #endif
  51
  52 #include <sigsegv.h>
  53
  54 #include "exitfail.h"
  55 #include "idx.h"
  56 #include "ignore-value.h"
  57
  58 #include "gettext.h"
  59 #define _(msgid) gettext (msgid)
  60
  61 #if HAVE_STACK_OVERFLOW_RECOVERY
  62
  63 /* Storage for the alternate signal stack.
  64    64 KiB is not too large for Gnulib-using apps, and is large enough
  65    for all known platforms.  Smaller sizes may run into trouble.
  66    For example, libsigsegv 2.6 through 2.8 have a bug where some
  67    architectures use more than the Linux default of an 8 KiB alternate
  68    stack when deciding if a fault was caused by stack overflow.  */
  69 static max_align_t alternate_signal_stack[(64 * 1024
  70                                            + sizeof (max_align_t) - 1)
  71                                           / sizeof (max_align_t)];
  72
  73 /* The user-specified action to take when a SEGV-related program error
  74    or stack overflow occurs.  */
  75 static _GL_ASYNC_SAFE void (* volatile segv_action) (int);
  76
  77 /* Translated messages for program errors and stack overflow.  Do not
  78    translate them in the signal handler, since gettext is not
  79    async-signal-safe.  */
  80 static char const * volatile program_error_message;
  81 static char const * volatile stack_overflow_message;
  82
  83 /* Output an error message, then exit with status EXIT_FAILURE if it
  84    appears to have been a stack overflow, or with a core dump
  85    otherwise.  This function is async-signal-safe.  */
  86
  87 static char const * volatile progname;
  88
  89 static _GL_ASYNC_SAFE _Noreturn void
  90 die (int signo)
  91 {
  92   segv_action (signo);
  93   char const *message = signo ? program_error_message : stack_overflow_message;
  94
  95   /* If the message is short, write it all at once to avoid
  96      interleaving with other messages.  Avoid writev as it is not
  97      documented to be async-signal-safe.  */
  98   size_t prognamelen = strlen (progname);
  99   size_t messagelen = strlen (message);
 100   static char const separator[] = {':', ' '};
 101   char buf[sizeof alternate_signal_stack / 16 + sizeof separator];
 102   idx_t buflen;
 103   if (prognamelen + messagelen < sizeof buf - sizeof separator)
 104     {
 105       char *p = mempcpy (buf, progname, prognamelen);
 106       p = mempcpy (p, separator, sizeof separator);
 107       p = mempcpy (p, message, messagelen);
 108       *p++ = '\n';
 109       buflen = p - buf;
 110     }
 111   else
 112     {
 113       ignore_value (write (STDERR_FILENO, progname, prognamelen));
 114       ignore_value (write (STDERR_FILENO, separator, sizeof separator));
 115       ignore_value (write (STDERR_FILENO, message, messagelen));
 116       buf[0] = '\n';
 117       buflen = 1;
 118     }
 119   ignore_value (write (STDERR_FILENO, buf, buflen));
 120
 121   if (! signo)
 122     _exit (exit_failure);
 123   raise (signo);
 124   abort ();
 125 }
 126
 127 static _GL_ASYNC_SAFE void
 128 null_action (_GL_UNUSED int signo)
 129 {
 130 }
 131
 132 /* Pacify GCC 9.3.1, which otherwise would complain about segv_handler.  */
 133 # if 4 < __GNUC__ + (6 <= __GNUC_MINOR__)
 134 #  pragma GCC diagnostic ignored "-Wsuggest-attribute=pure"
 135 # endif
 136
 137 /* Nonzero if general segv handler could not be installed.  */
 138 static volatile int segv_handler_missing;
 139
 140 /* Handle a segmentation violation and exit if it cannot be stack
 141    overflow.  This function is async-signal-safe.  */
 142
 143 static _GL_ASYNC_SAFE int
 144 segv_handler (_GL_UNUSED void *address, int serious)
 145 {
 146 # if DEBUG
 147   {
 148     char buf[1024];
 149     int saved_errno = errno;
 150     ignore_value (write (STDERR_FILENO, buf,
 151                          sprintf (buf, "segv_handler serious=%d\n", serious)));
 152     errno = saved_errno;
 153   }
 154 # endif
 155
 156   /* If this fault is not serious, return 0 to let the stack overflow
 157      handler take a shot at it.  */
 158   if (!serious)
 159     return 0;
 160   die (SIGSEGV);
 161 }
 162
 163 /* Handle a segmentation violation that is likely to be a stack
 164    overflow and exit.  This function is async-signal-safe.  */
 165
 166 static _GL_ASYNC_SAFE _Noreturn void
 167 overflow_handler (int emergency, _GL_UNUSED stackoverflow_context_t context)
 168 {
 169 # if DEBUG
 170   {
 171     char buf[1024];
 172     ignore_value (write (STDERR_FILENO, buf,
 173                          sprintf (buf, ("overflow_handler emergency=%d"
 174                                         " segv_handler_missing=%d\n"),
 175                                   emergency, segv_handler_missing)));
 176   }
 177 # endif
 178
 179   die ((!emergency || segv_handler_missing) ? 0 : SIGSEGV);
 180 }
 181
 182 int
 183 c_stack_action (_GL_ASYNC_SAFE void (*action) (int))
 184 {
 185   segv_action = action ? action : null_action;
 186   program_error_message = _("program error");
 187   stack_overflow_message = _("stack overflow");
 188   progname = getprogname ();
 189
 190   /* Always install the overflow handler.  */
 191   if (stackoverflow_install_handler (overflow_handler,
 192                                      alternate_signal_stack,
 193                                      sizeof alternate_signal_stack))
 194     {
 195       errno = ENOTSUP;
 196       return -1;
 197     }
 198   /* Try installing a general handler; if it fails, then treat all
 199      segv as stack overflow.  */
 200   segv_handler_missing = sigsegv_install_handler (segv_handler);
 201   return 0;
 202 }
 203
 204 #else /* !HAVE_STACK_OVERFLOW_RECOVERY */
 205
 206 int
 207 c_stack_action (_GL_ASYNC_SAFE void (*action) (_GL_UNUSED int) )
 208 {
 209   errno = ENOTSUP;
 210   return -1;
 211 }
 212
 213 #endif