contrib/diffutils/lib/c-stack.c

   1 /* Stack overflow handling.
   2
   3    Copyright (C) 2002, 2004, 2006, 2008-2013 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 <http://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 #ifndef __attribute__
  39 # if __GNUC__ < 3
  40 #  define __attribute__(x)
  41 # endif
  42 #endif
  43
  44 #include "gettext.h"
  45 #define _(msgid) gettext (msgid)
  46
  47 #include <errno.h>
  48
  49 #include <signal.h>
  50 #if ! HAVE_STACK_T && ! defined stack_t
  51 typedef struct sigaltstack stack_t;
  52 #endif
  53 #ifndef SIGSTKSZ
  54 # define SIGSTKSZ 16384
  55 #elif HAVE_LIBSIGSEGV && SIGSTKSZ < 16384
  56 /* libsigsegv 2.6 through 2.8 have a bug where some architectures use
  57    more than the Linux default of an 8k alternate stack when deciding
  58    if a fault was caused by stack overflow.  */
  59 # undef SIGSTKSZ
  60 # define SIGSTKSZ 16384
  61 #endif
  62
  63 #include <stdlib.h>
  64 #include <string.h>
  65
  66 /* Posix 2001 declares ucontext_t in <ucontext.h>, Posix 200x in
  67    <signal.h>.  */
  68 #if HAVE_UCONTEXT_H
  69 # include <ucontext.h>
  70 #endif
  71
  72 #include <unistd.h>
  73
  74 #if HAVE_LIBSIGSEGV
  75 # include <sigsegv.h>
  76 #endif
  77
  78 #include "c-stack.h"
  79 #include "exitfail.h"
  80 #include "ignore-value.h"
  81
  82 #if defined SA_ONSTACK && defined SA_SIGINFO
  83 # define SIGINFO_WORKS 1
  84 #else
  85 # define SIGINFO_WORKS 0
  86 # ifndef SA_ONSTACK
  87 #  define SA_ONSTACK 0
  88 # endif
  89 #endif
  90
  91 extern char *program_name;
  92
  93 /* The user-specified action to take when a SEGV-related program error
  94    or stack overflow occurs.  */
  95 static void (* volatile segv_action) (int);
  96
  97 /* Translated messages for program errors and stack overflow.  Do not
  98    translate them in the signal handler, since gettext is not
  99    async-signal-safe.  */
 100 static char const * volatile program_error_message;
 101 static char const * volatile stack_overflow_message;
 102
 103 /* Output an error message, then exit with status EXIT_FAILURE if it
 104    appears to have been a stack overflow, or with a core dump
 105    otherwise.  This function is async-signal-safe.  */
 106
 107 static _Noreturn void
 108 die (int signo)
 109 {
 110   char const *message;
 111 #if !SIGINFO_WORKS && !HAVE_LIBSIGSEGV
 112   /* We can't easily determine whether it is a stack overflow; so
 113      assume that the rest of our program is perfect (!) and that
 114      this segmentation violation is a stack overflow.  */
 115   signo = 0;
 116 #endif /* !SIGINFO_WORKS && !HAVE_LIBSIGSEGV */
 117   segv_action (signo);
 118   message = signo ? program_error_message : stack_overflow_message;
 119   ignore_value (write (STDERR_FILENO, program_name, strlen (program_name)));
 120   ignore_value (write (STDERR_FILENO, ": ", 2));
 121   ignore_value (write (STDERR_FILENO, message, strlen (message)));
 122   ignore_value (write (STDERR_FILENO, "\n", 1));
 123   if (! signo)
 124     _exit (exit_failure);
 125   raise (signo);
 126   abort ();
 127 }
 128
 129 #if (HAVE_SIGALTSTACK && HAVE_DECL_SIGALTSTACK \
 130      && HAVE_STACK_OVERFLOW_HANDLING) || HAVE_LIBSIGSEGV
 131
 132 /* Storage for the alternate signal stack.  */
 133 static union
 134 {
 135   char buffer[SIGSTKSZ];
 136
 137   /* These other members are for proper alignment.  There's no
 138      standard way to guarantee stack alignment, but this seems enough
 139      in practice.  */
 140   long double ld;
 141   long l;
 142   void *p;
 143 } alternate_signal_stack;
 144
 145 static void
 146 null_action (int signo __attribute__ ((unused)))
 147 {
 148 }
 149
 150 #endif /* SIGALTSTACK || LIBSIGSEGV */
 151
 152 /* Only use libsigsegv if we need it; platforms like Solaris can
 153    detect stack overflow without the overhead of an external
 154    library.  */
 155 #if HAVE_LIBSIGSEGV && ! HAVE_XSI_STACK_OVERFLOW_HEURISTIC
 156
 157 /* Nonzero if general segv handler could not be installed.  */
 158 static volatile int segv_handler_missing;
 159
 160 /* Handle a segmentation violation and exit if it cannot be stack
 161    overflow.  This function is async-signal-safe.  */
 162
 163 static int segv_handler (void *address __attribute__ ((unused)),
 164                          int serious)
 165 {
 166 # if DEBUG
 167   {
 168     char buf[1024];
 169     sprintf (buf, "segv_handler serious=%d\n", serious);
 170     write (STDERR_FILENO, buf, strlen (buf));
 171   }
 172 # endif
 173
 174   /* If this fault is not serious, return 0 to let the stack overflow
 175      handler take a shot at it.  */
 176   if (!serious)
 177     return 0;
 178   die (SIGSEGV);
 179 }
 180
 181 /* Handle a segmentation violation that is likely to be a stack
 182    overflow and exit.  This function is async-signal-safe.  */
 183
 184 static _Noreturn void
 185 overflow_handler (int emergency,
 186                   stackoverflow_context_t context __attribute__ ((unused)))
 187 {
 188 # if DEBUG
 189   {
 190     char buf[1024];
 191     sprintf (buf, "overflow_handler emergency=%d segv_handler_missing=%d\n",
 192              emergency, segv_handler_missing);
 193     write (STDERR_FILENO, buf, strlen (buf));
 194   }
 195 # endif
 196
 197   die ((!emergency || segv_handler_missing) ? 0 : SIGSEGV);
 198 }
 199
 200 int
 201 c_stack_action (void (*action) (int))
 202 {
 203   segv_action = action ? action : null_action;
 204   program_error_message = _("program error");
 205   stack_overflow_message = _("stack overflow");
 206
 207   /* Always install the overflow handler.  */
 208   if (stackoverflow_install_handler (overflow_handler,
 209                                      alternate_signal_stack.buffer,
 210                                      sizeof alternate_signal_stack.buffer))
 211     {
 212       errno = ENOTSUP;
 213       return -1;
 214     }
 215   /* Try installing a general handler; if it fails, then treat all
 216      segv as stack overflow.  */
 217   segv_handler_missing = sigsegv_install_handler (segv_handler);
 218   return 0;
 219 }
 220
 221 #elif HAVE_SIGALTSTACK && HAVE_DECL_SIGALTSTACK && HAVE_STACK_OVERFLOW_HANDLING
 222
 223 # if SIGINFO_WORKS
 224
 225 /* Handle a segmentation violation and exit.  This function is
 226    async-signal-safe.  */
 227
 228 static _Noreturn void
 229 segv_handler (int signo, siginfo_t *info,
 230               void *context __attribute__ ((unused)))
 231 {
 232   /* Clear SIGNO if it seems to have been a stack overflow.  */
 233 #  if ! HAVE_XSI_STACK_OVERFLOW_HEURISTIC
 234   /* We can't easily determine whether it is a stack overflow; so
 235      assume that the rest of our program is perfect (!) and that
 236      this segmentation violation is a stack overflow.
 237
 238      Note that although both Linux and Solaris provide
 239      sigaltstack, SA_ONSTACK, and SA_SIGINFO, currently only
 240      Solaris satisfies the XSI heuristic.  This is because
 241      Solaris populates uc_stack with the details of the
 242      interrupted stack, while Linux populates it with the details
 243      of the current stack.  */
 244   signo = 0;
 245 #  else
 246   if (0 < info->si_code)
 247     {
 248       /* If the faulting address is within the stack, or within one
 249          page of the stack, assume that it is a stack overflow.  */
 250       ucontext_t const *user_context = context;
 251       char const *stack_base = user_context->uc_stack.ss_sp;
 252       size_t stack_size = user_context->uc_stack.ss_size;
 253       char const *faulting_address = info->si_addr;
 254       size_t page_size = sysconf (_SC_PAGESIZE);
 255       size_t s = faulting_address - stack_base + page_size;
 256       if (s < stack_size + 2 * page_size)
 257         signo = 0;
 258
 259 #   if DEBUG
 260       {
 261         char buf[1024];
 262         sprintf (buf,
 263                  "segv_handler fault=%p base=%p size=%lx page=%lx signo=%d\n",
 264                  faulting_address, stack_base, (unsigned long) stack_size,
 265                  (unsigned long) page_size, signo);
 266         write (STDERR_FILENO, buf, strlen (buf));
 267       }
 268 #   endif
 269     }
 270 #  endif
 271
 272   die (signo);
 273 }
 274 # endif
 275
 276 int
 277 c_stack_action (void (*action) (int))
 278 {
 279   int r;
 280   stack_t st;
 281   struct sigaction act;
 282   st.ss_flags = 0;
 283 # if SIGALTSTACK_SS_REVERSED
 284   /* Irix mistakenly treats ss_sp as the upper bound, rather than
 285      lower bound, of the alternate stack.  */
 286   st.ss_sp = alternate_signal_stack.buffer + SIGSTKSZ - sizeof (void *);
 287   st.ss_size = sizeof alternate_signal_stack.buffer - sizeof (void *);
 288 # else
 289   st.ss_sp = alternate_signal_stack.buffer;
 290   st.ss_size = sizeof alternate_signal_stack.buffer;
 291 # endif
 292   r = sigaltstack (&st, NULL);
 293   if (r != 0)
 294     return r;
 295
 296   segv_action = action ? action : null_action;
 297   program_error_message = _("program error");
 298   stack_overflow_message = _("stack overflow");
 299
 300   sigemptyset (&act.sa_mask);
 301
 302 # if SIGINFO_WORKS
 303   /* POSIX 1003.1-2001 says SA_RESETHAND implies SA_NODEFER, but
 304      this is not true on Solaris 8 at least.  It doesn't hurt to use
 305      SA_NODEFER here, so leave it in.  */
 306   act.sa_flags = SA_NODEFER | SA_ONSTACK | SA_RESETHAND | SA_SIGINFO;
 307   act.sa_sigaction = segv_handler;
 308 # else
 309   act.sa_flags = SA_NODEFER | SA_ONSTACK | SA_RESETHAND;
 310   act.sa_handler = die;
 311 # endif
 312
 313 # if FAULT_YIELDS_SIGBUS
 314   if (sigaction (SIGBUS, &act, NULL) < 0)
 315     return -1;
 316 # endif
 317   return sigaction (SIGSEGV, &act, NULL);
 318 }
 319
 320 #else /* ! ((HAVE_SIGALTSTACK && HAVE_DECL_SIGALTSTACK
 321              && HAVE_STACK_OVERFLOW_HANDLING) || HAVE_LIBSIGSEGV) */
 322
 323 int
 324 c_stack_action (void (*action) (int)  __attribute__ ((unused)))
 325 {
 326   errno = ENOTSUP;
 327   return -1;
 328 }
 329
 330 #endif