/*      $NetBSD: c-stack.c,v 1.1.1.1 2016/01/13 03:15:30 christos Exp $ */

/* Stack overflow handling.

  Copyright (C) 2002 Free Software Foundation, Inc.

  This program is free software; you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation; either version 2, or (at your option)
  any later version.

  This program 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 General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with this program; if not, write to the Free Software Foundation,
  Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */

/* Written by Paul Eggert.  */

/* This module assumes that each stack frame is smaller than a page.
  If you use alloca, dynamic arrays, or large local variables, your
  program may extend the stack by more than a page at a time.  If so,
  the code below may incorrectly report a program error, or worse
  yet, may not detect the overflow at all.  To avoid this problem,
  don't use large local arrays.  */

#if HAVE_CONFIG_H
# include <config.h>
#endif

#include "gettext.h"
#define _(msgid) gettext (msgid)

#include <errno.h>
#ifndef ENOTSUP
# define ENOTSUP EINVAL
#endif

#if HAVE_INTTYPES_H
# include <inttypes.h>
#else
# if HAVE_STDINT_H
#  include <stdint.h>
# endif
#endif

#include <signal.h>
#include <stdlib.h>
#include <string.h>

#if HAVE_UNISTD_H
# include <unistd.h>
#endif
#ifndef STDERR_FILENO
# define STDERR_FILENO 2
#endif

#include "c-stack.h"
#include "exitfail.h"

extern char *program_name;

#if HAVE_XSI_STACK_OVERFLOW_HEURISTIC

# include <ucontext.h>


/* Storage for the alternate signal stack.  */
static union
{
 char buffer[SIGSTKSZ];

 /* These other members are for proper alignment.  There's no
    standard way to guarantee stack alignment, but this seems enough
    in practice.  */
 long double ld;
 uintmax_t u;
 void *p;
} alternate_signal_stack;


/* Direction of the C runtime stack.  This function is
  async-signal-safe.  */

# if STACK_DIRECTION
#  define find_stack_direction(ptr) STACK_DIRECTION
# else
static int
find_stack_direction (char const *addr)
{
 char dummy;
 return ! addr ? find_stack_direction (&dummy) : addr < &dummy ? 1 : -1;
}
# endif

/* The SIGSEGV handler.  */
static void (* volatile segv_action) (int, siginfo_t *, void *);

/* Handle a segmentation violation and exit.  This function is
  async-signal-safe.  */

static void
segv_handler (int signo, siginfo_t *info, void *context)
{
 /* Clear SIGNO if it seems to have been a stack overflow.  */
 if (0 < info->si_code)
   {
     /* If the faulting address is within the stack, or within one
        page of the stack end, assume that it is a stack
        overflow.  */
     ucontext_t const *user_context = context;
     char const *stack_min = user_context->uc_stack.ss_sp;
     size_t stack_size = user_context->uc_stack.ss_size;
     char const *faulting_address = info->si_addr;
     size_t s = faulting_address - stack_min;
     size_t page_size = sysconf (_SC_PAGESIZE);
     if (find_stack_direction (0) < 0)
       s += page_size;
     if (s < stack_size + page_size)
       signo = 0;
   }

 segv_action (signo, info, context);
}

#endif /* HAVE_XSI_STACK_OVERFLOW_HEURISTIC */


/* Translated messages for program errors and stack overflow.  Do not
  translate them in the signal handler, since gettext is not
  async-signal-safe.  */
static char const * volatile program_error_message;
static char const * volatile stack_overflow_message;

/* Output an error message, then exit with status EXIT_FAILURE if it
  appears to have been a stack overflow, or with a core dump
  otherwise.  This function is async-signal-safe.  */

void
c_stack_die (int signo, siginfo_t *info, void *context)
{
 char const *message =
   signo ? program_error_message : stack_overflow_message;
 write (STDERR_FILENO, program_name, strlen (program_name));
 write (STDERR_FILENO, ": ", 2);
 write (STDERR_FILENO, message, strlen (message));
 write (STDERR_FILENO, "\n", 1);
 if (! signo)
   _exit (exit_failure);
#if HAVE_SIGINFO_T
 if (context && info && 0 <= info->si_code)
   {
     /* Re-raise the exception at the same address.  */
     char *addr = info->si_addr;
     *addr = 0;
   }
#endif
 kill (getpid (), signo);
}


/* Set up ACTION so that it is invoked on C stack overflow.  Return -1
  (setting errno) if this cannot be done.

  ACTION must invoke only async-signal-safe functions.  ACTION
  together with its callees must not require more than SIGSTKSZ bytes
  of stack space.  */

int
c_stack_action (void (*action) (int, siginfo_t *, void *))
{
#if ! HAVE_XSI_STACK_OVERFLOW_HEURISTIC
 errno = ENOTSUP;
 return -1;
#else
 struct sigaction act;
 stack_t st;
 int r;

 st.ss_flags = 0;
 st.ss_sp = alternate_signal_stack.buffer;
 st.ss_size = sizeof alternate_signal_stack.buffer;
 r = sigaltstack (&st, 0);
 if (r != 0)
   return r;

 program_error_message = _("program error");
 stack_overflow_message = _("stack overflow");
 segv_action = action;

 sigemptyset (&act.sa_mask);

 /* POSIX 1003.1-2001 says SA_RESETHAND implies SA_NODEFER, but this
    is not true on Solaris 8 at least.  It doesn't hurt to use
    SA_NODEFER here, so leave it in.  */
 act.sa_flags = SA_NODEFER | SA_ONSTACK | SA_RESETHAND | SA_SIGINFO;

 act.sa_sigaction = segv_handler;
 return sigaction (SIGSEGV, &act, 0);
#endif
}

#if DEBUG

#include <stdio.h>

int volatile exit_failure;

static long
recurse (char *p)
{
 char array[500];
 array[0] = 1;
 return *p + recurse (array);
}

char *program_name;

int
main (int argc, char **argv)
{
 program_name = argv[0];
 c_stack_action (c_stack_die);
 return recurse ("\1");
}

#endif /* DEBUG */

/*
Local Variables:
compile-command: "gcc -D_GNU_SOURCE -DDEBUG \
 -DHAVE_INTTYPES_H -DHAVE_SIGINFO_T \
 -DHAVE_XSI_STACK_OVERFLOW_HEURISTIC -DHAVE_UNISTD_H \
 -Wall -W -g c-stack.c -o c-stack"
End:
*/