lib/c-stack.c

   1 /* Stack overflow handling.
   2
   3    Copyright (C) 2002 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 2, or (at your option)
   8    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, write to the Free Software Foundation,
  17    Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
  18
  19 /* Written by Paul Eggert.  */
  20
  21 /* NOTES:
  22
  23    A program that uses alloca, dynamic arrays, or large local
  24    variables may extend the stack by more than a page at a time.  If
  25    so, when the stack overflows the operating system may not detect
  26    the overflow until the program uses the array, and this module may
  27    incorrectly report a program error instead of a stack overflow.
  28
  29    To avoid this problem, allocate only small objects on the stack; a
  30    program should be OK if it limits single allocations to a page or
  31    less.  Allocate larger arrays in static storage, or on the heap
  32    (e.g., with malloc).  Yes, this is a pain, but we don't know of any
  33    better solution that is portable.
  34
  35    No attempt has been made to deal with multithreaded applications.
  36
  37    If ! HAVE_XSI_STACK_OVERFLOW_HEURISTIC, the current implementation
  38    assumes that, if the RLIMIT_STACK limit changes during execution,
  39    then c_stack_action is invoked immediately afterwards.  */
  40
  41 #if HAVE_CONFIG_H
  42 # include <config.h>
  43 #endif
  44
  45 #ifndef __attribute__
  46 # if __GNUC__ < 3 || __STRICT_ANSI__
  47 #  define __attribute__(x)
  48 # endif
  49 #endif
  50
  51 #include "gettext.h"
  52 #define _(msgid) gettext (msgid)
  53
  54 #include <errno.h>
  55 #ifndef ENOTSUP
  56 # define ENOTSUP EINVAL
  57 #endif
  58 #ifndef EOVERFLOW
  59 # define EOVERFLOW EINVAL
  60 #endif
  61
  62 #include <signal.h>
  63 #if ! HAVE_STACK_T && ! defined stack_t
  64 typedef struct sigaltstack stack_t;
  65 #endif
  66
  67 #include <stdlib.h>
  68 #include <string.h>
  69
  70 #if HAVE_SYS_RESOURCE_H
  71 /* Include sys/time.h here, because...
  72    SunOS-4.1.x <sys/resource.h> fails to include <sys/time.h>.
  73    This gives "incomplete type" errors for ru_utime and tu_stime.  */
  74 # if HAVE_SYS_TIME_H
  75 #  include <sys/time.h>
  76 # endif
  77 # include <sys/resource.h>
  78 #endif
  79
  80 #if HAVE_UCONTEXT_H
  81 # include <ucontext.h>
  82 #endif
  83
  84 #if HAVE_UNISTD_H
  85 # include <unistd.h>
  86 #endif
  87 #ifndef STDERR_FILENO
  88 # define STDERR_FILENO 2
  89 #endif
  90
  91 #if DEBUG
  92 # include <stdio.h>
  93 #endif
  94
  95 #include "c-stack.h"
  96 #include "exitfail.h"
  97
  98 extern char *program_name;
  99
 100 /* The user-specified action to take when a SEGV-related program error
 101    or stack overflow occurs.  */
 102 static void (* volatile segv_action) (int);
 103
 104 /* Translated messages for program errors and stack overflow.  Do not
 105    translate them in the signal handler, since gettext is not
 106    async-signal-safe.  */
 107 static char const * volatile program_error_message;
 108 static char const * volatile stack_overflow_message;
 109
 110 /* Output an error message, then exit with status EXIT_FAILURE if it
 111    appears to have been a stack overflow, or with a core dump
 112    otherwise.  This function is async-signal-safe.  */
 113
 114 static void die (int) __attribute__ ((noreturn));
 115 static void
 116 die (int signo)
 117 {
 118   char const *message =
 119     signo ? program_error_message : stack_overflow_message;
 120   segv_action (signo);
 121   write (STDERR_FILENO, program_name, strlen (program_name));
 122   write (STDERR_FILENO, ": ", 2);
 123   write (STDERR_FILENO, message, strlen (message));
 124   write (STDERR_FILENO, "\n", 1);
 125   if (! signo)
 126     _exit (exit_failure);
 127   kill (getpid (), signo);
 128   abort ();
 129 }
 130
 131 #if HAVE_SIGALTSTACK && HAVE_DECL_SIGALTSTACK
 132
 133 /* Direction of the C runtime stack.  This function is
 134    async-signal-safe.  */
 135
 136 # if STACK_DIRECTION
 137 #  define find_stack_direction(ptr) STACK_DIRECTION
 138 # else
 139 static int
 140 find_stack_direction (char const *addr)
 141 {
 142   char dummy;
 143   return ! addr ? find_stack_direction (&dummy) : addr < &dummy ? 1 : -1;
 144 }
 145 # endif
 146
 147 # if HAVE_XSI_STACK_OVERFLOW_HEURISTIC
 148 #  define get_stack_location(argv) 0
 149 # else
 150
 151 #  if defined RLIMIT_STACK && defined _SC_PAGESIZE
 152
 153 /* Return the minimum machine address deducible from ARGV.  This
 154    includes the addresses of all the strings that ARGV points at, as
 155    well as the address of ARGV itself.  */
 156
 157 static char const *
 158 min_address_from_argv (char * const *argv)
 159 {
 160   char const *min = (char const *) argv;
 161   char const *p;
 162   while ((p = *argv++))
 163     if (p < min)
 164       min = p;
 165   return min;
 166 }
 167
 168 /* Return the maximum machine address deducible from ARGV.  */
 169
 170 static char const *
 171 max_address_from_argv (char * const *argv)
 172 {
 173   char const *max = *argv;
 174   char const *max1;
 175   char const *p;
 176   while ((p = *argv++))
 177     if (max < p)
 178       max = p;
 179   max1 = (char const *) (argv + 1);
 180   return max && max1 < max ? max + strlen (max) + 1 : max1;
 181 }
 182 #  endif
 183
 184 /* The base and size of the stack, determined at startup.  */
 185 static char const * volatile stack_base;
 186 static size_t volatile stack_size;
 187
 188 /* Store the base and size of the stack into the static variables
 189    STACK_BASE and STACK_SIZE.  The base is the numerically lowest
 190    address in the stack.  Return -1 (setting errno) if this cannot be
 191    done.  */
 192
 193 static int
 194 get_stack_location (char * const *argv)
 195 {
 196 #  if ! (defined RLIMIT_STACK && defined _SC_PAGESIZE)
 197
 198   errno = ENOTSUP;
 199   return -1;
 200
 201 #  else
 202
 203   struct rlimit rlimit;
 204   int r = getrlimit (RLIMIT_STACK, &rlimit);
 205   if (r == 0)
 206     {
 207       char const *base;
 208       size_t size = rlimit.rlim_cur;
 209       extern char **environ;
 210       size_t page_size = sysconf (_SC_PAGESIZE);
 211       int stack_direction = find_stack_direction (0);
 212
 213 #   if HAVE_GETCONTEXT && HAVE_DECL_GETCONTEXT
 214       ucontext_t context;
 215       if (getcontext (&context) == 0)
 216         {
 217           base = context.uc_stack.ss_sp;
 218           if (stack_direction < 0)
 219             base -= size - context.uc_stack.ss_size;
 220         }
 221       else
 222 #   endif
 223         {
 224           if (stack_direction < 0)
 225             {
 226               char const *a = max_address_from_argv (argv);
 227               char const *b = max_address_from_argv (environ);
 228               base = (a < b ? b : a) - size;
 229               base += - (size_t) base % page_size;
 230             }
 231           else
 232             {
 233               char const *a = min_address_from_argv (argv);
 234               char const *b = min_address_from_argv (environ);
 235               base = a < b ? a : b;
 236               base -= (size_t) base % page_size;
 237             }
 238         }
 239
 240       if (size != rlimit.rlim_cur
 241           || rlimit.rlim_cur < 0
 242           || base + size < base
 243 #   ifdef RLIM_SAVED_CUR
 244           || rlimit.rlim_cur == RLIM_SAVED_CUR
 245 #   endif
 246 #   ifdef RLIM_SAVED_MAX
 247           || rlimit.rlim_cur == RLIM_SAVED_MAX
 248 #   endif
 249 #   ifdef RLIM_INFINITY
 250           || rlimit.rlim_cur == RLIM_INFINITY
 251 #   endif
 252           )
 253         {
 254           errno = EOVERFLOW;
 255           return -1;
 256         }
 257
 258       stack_base = base;
 259       stack_size = size;
 260
 261 #   if DEBUG
 262       fprintf (stderr, "get_stack_location base=%p size=%lx\n",
 263                base, (unsigned long) size);
 264 #   endif
 265     }
 266
 267   return r;
 268
 269 #  endif
 270 }
 271 # endif
 272
 273 /* Storage for the alternate signal stack.  */
 274 static union
 275 {
 276   char buffer[SIGSTKSZ];
 277
 278   /* These other members are for proper alignment.  There's no
 279      standard way to guarantee stack alignment, but this seems enough
 280      in practice.  */
 281   long double ld;
 282   long l;
 283   void *p;
 284 } alternate_signal_stack;
 285
 286 # if defined SA_ONSTACK && defined SA_SIGINFO && defined _SC_PAGESIZE
 287
 288 /* Handle a segmentation violation and exit.  This function is
 289    async-signal-safe.  */
 290
 291 static void segv_handler (int, siginfo_t *, void *) __attribute__((noreturn));
 292 static void
 293 segv_handler (int signo, siginfo_t *info,
 294               void *context __attribute__ ((unused)))
 295 {
 296   /* Clear SIGNO if it seems to have been a stack overflow.  */
 297   if (0 < info->si_code)
 298     {
 299       /* If the faulting address is within the stack, or within one
 300          page of the stack end, assume that it is a stack
 301          overflow.  */
 302 #  if HAVE_XSI_STACK_OVERFLOW_HEURISTIC
 303       ucontext_t const *user_context = context;
 304       char const *stack_base = user_context->uc_stack.ss_sp;
 305       size_t stack_size = user_context->uc_stack.ss_size;
 306 #  endif
 307       char const *faulting_address = info->si_addr;
 308       size_t s = faulting_address - stack_base;
 309       size_t page_size = sysconf (_SC_PAGESIZE);
 310       if (find_stack_direction (0) < 0)
 311         s += page_size;
 312       if (s < stack_size + page_size)
 313         signo = 0;
 314
 315 #  if DEBUG
 316       {
 317         char buf[1024];
 318         sprintf (buf,
 319                  "segv_handler fault=%p base=%p size=%lx page=%lx signo=%d\n",
 320                  faulting_address, stack_base, (unsigned long) stack_size,
 321                  (unsigned long) page_size, signo);
 322         write (STDERR_FILENO, buf, strlen (buf));
 323       }
 324 #  endif
 325     }
 326
 327   die (signo);
 328 }
 329 # endif
 330
 331 static void
 332 null_action (int signo __attribute__ ((unused)))
 333 {
 334 }
 335
 336 /* Assuming ARGV is the argument vector of `main', set up ACTION so
 337    that it is invoked on C stack overflow.  Return -1 (setting errno)
 338    if this cannot be done.
 339
 340    When ACTION is called, it is passed an argument equal to SIGSEGV
 341    for a segmentation violation that does not appear related to stack
 342    overflow, and is passed zero otherwise.
 343
 344    A null ACTION acts like an action that does nothing.
 345
 346    ACTION must be async-signal-safe.  ACTION together with its callees
 347    must not require more than SIGSTKSZ bytes of stack space.  */
 348
 349 int
 350 c_stack_action (char * const *argv __attribute__ ((unused)),
 351                 void (*action) (int))
 352 {
 353   int r = get_stack_location (argv);
 354   if (r != 0)
 355     return r;
 356
 357   {
 358     stack_t st;
 359     st.ss_flags = 0;
 360     st.ss_sp = alternate_signal_stack.buffer;
 361     st.ss_size = sizeof alternate_signal_stack.buffer;
 362     r = sigaltstack (&st, 0);
 363     if (r != 0)
 364       return r;
 365   }
 366
 367   segv_action = action ? action : null_action;
 368   program_error_message = _("program error");
 369   stack_overflow_message = _("stack overflow");
 370
 371   {
 372 # if ! (defined SA_ONSTACK && defined SA_SIGINFO && defined _SC_PAGESIZE)
 373     return signal (SIGSEGV, die) == SIG_ERR ? -1 : 0;
 374 # else
 375     struct sigaction act;
 376     sigemptyset (&act.sa_mask);
 377
 378     /* POSIX 1003.1-2001 says SA_RESETHAND implies SA_NODEFER, but
 379        this is not true on Solaris 8 at least.  It doesn't hurt to use
 380        SA_NODEFER here, so leave it in.  */
 381     act.sa_flags = SA_NODEFER | SA_ONSTACK | SA_RESETHAND | SA_SIGINFO;
 382
 383     act.sa_sigaction = segv_handler;
 384
 385     return sigaction (SIGSEGV, &act, 0);
 386 # endif
 387   }
 388 }
 389
 390 #else /* ! (HAVE_SIGALTSTACK && HAVE_DECL_SIGALTSTACK) */
 391
 392 int
 393 c_stack_action (char * const *argv __attribute__ ((unused)),
 394                 void (*action) (int)  __attribute__ ((unused)))
 395 {
 396   errno = ENOTSUP;
 397   return -1;
 398 }
 399
 400 #endif
 401
 402 \f
 403
 404 #if DEBUG
 405
 406 int volatile exit_failure;
 407
 408 static long
 409 recurse (char *p)
 410 {
 411   char array[500];
 412   array[0] = 1;
 413   return *p + recurse (array);
 414 }
 415
 416 char *program_name;
 417
 418 int
 419 main (int argc __attribute__ ((unused)), char **argv)
 420 {
 421   program_name = argv[0];
 422   fprintf (stderr, "The last line of output should be \"stack overflow\".\n");
 423   if (c_stack_action (argv, 0) == 0)
 424     return recurse ("\1");
 425   perror ("c_stack_action");
 426   return 1;
 427 }
 428
 429 #endif /* DEBUG */
 430 \f
 431 /*
 432 Local Variables:
 433 compile-command: "gcc -DDEBUG -DHAVE_CONFIG_H -I.. -g -O -Wall -W c-stack.c"
 434 End:
 435 */