check_stack.cc

/* Copyright (c) 2016, 2024, Oracle and/or its affiliates.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License, version 2.0,
   as published by the Free Software Foundation.

   This program is designed to work with certain software (including
   but not limited to OpenSSL) that is licensed under separate terms,
   as designated in a particular file or component or in included license
   documentation.  The authors of MySQL hereby grant you an additional
   permission to link the program and your derivative works with the
   separately licensed software that they have either included with
   the program or referenced in the documentation.

   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, version 2.0, 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., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */

#include "sql/check_stack.h"

#include "my_config.h"

#include <assert.h>
#include <stdio.h>
#include <algorithm>
#include <atomic>
#include <new>

#include "my_compiler.h"
#include "my_dbug.h"
#include "my_inttypes.h"
#include "my_sys.h"
#include "mysql_com.h"
#include "mysqld_error.h"
#include "sql/current_thd.h"
#include "sql/derror.h"
#include "sql/sql_class.h"

/****************************************************************************
        Check stack size; Send error if there isn't enough stack to continue
****************************************************************************/

namespace {
int stack_direction = 0;
}

NO_INLINE
int stack_direction_f(int *a) {
  int b;
  if (&b > a) {
    // printf("Stack grows upward\n");
    return 1;
  }
  // printf("Stack grows downward\n");
  return 0;
}

/*
 Prevent compiler optimizations by calling function
 through pointer.
*/
int (*ptr_f)(int *) = stack_direction_f;

NO_INLINE
int initialize_stack_direction() {
  int a;
  const int retval = ptr_f(&a);
  if (retval == 0) {
    stack_direction = -1;
  } else {
    stack_direction = 1;
  }
  return retval;
}

namespace {
long used_stack(const char *a_ptr, const char *b_ptr) {
  if (stack_direction < 0) return a_ptr - b_ptr;
  return b_ptr - a_ptr;
}
}  // namespace

#ifndef NDEBUG
std::atomic<long> max_stack_used;
#endif

/**
  Check stack for a overrun

  @param thd            Thread handler.
  @param margin         Minimal acceptable unused space in the stack.
  @param buf            See a note below.

  @returns false if success, true if error (reported).

  @note
  Note: The 'buf' parameter is necessary, and we must have code which uses it.
  - Some of the fix_fields functions have a "dummy" buffer large enough for the
    corresponding execution. (Thus we only have to check in fix_fields.)
  - Passing the buffer to check_stack_overrun() prevents the compiler from
    removing it.
  - For -flto builds, the dummy buffer may be optimized away,
    so we need to write something into it.
*/
bool check_stack_overrun(const THD *thd, long margin, unsigned char *buf) {
  assert(thd == current_thd);
  assert(stack_direction == -1 || stack_direction == 1);

#if defined(HAVE_ASAN)
  // Stack grows upward, but our address computations do not work with
  // the "fake stack" of ASAN. Just return OK.
  // With ASAN_OPTIONS=detect_stack_use_after_return=true
  // any test which deliberately runs out of stack
  // (expects ER_STACK_OVERRUN_NEED_MORE) will most likely crash.
  if (stack_direction == 1) {
    return false;
  }
#endif

  long stack_used =
      used_stack(thd->thread_stack, reinterpret_cast<char *>(&stack_used));
  if (stack_used >= static_cast<long>(my_thread_stack_size - margin) ||
      DBUG_EVALUATE_IF("simulate_stack_overrun", true, false)) {
    // Touch the buffer, so that it is not optimized away by -flto.
    if (buf != nullptr) buf[0] = '\0';

    /*
      Do not use stack for the message buffer to ensure correct
      behaviour in cases we have close to no stack left.
    */
    char *ebuff = new (std::nothrow) char[MYSQL_ERRMSG_SIZE];
    if (ebuff) {
      snprintf(ebuff, MYSQL_ERRMSG_SIZE,
               ER_THD(thd, ER_STACK_OVERRUN_NEED_MORE), stack_used,
               my_thread_stack_size, margin);
      my_message(ER_STACK_OVERRUN_NEED_MORE, ebuff, MYF(ME_FATALERROR));
      delete[] ebuff;
    }
    return true;
  }
#ifndef NDEBUG
  max_stack_used = std::max(max_stack_used.load(), stack_used);
#endif
  return false;
}