glibc/malloc/mtrace.c

/* More debugging hooks for `malloc'.
   Copyright (C) 1991-2021 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
                 Written April 2, 1991 by John Gilmore of Cygnus Support.
                 Based on mcheck.c by Mike Haertel.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library 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
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

#ifndef _MALLOC_INTERNAL
# define _MALLOC_INTERNAL
# include <malloc.h>
# include <mcheck.h>
# include <libc-lock.h>
#endif

#include <dlfcn.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

#include <_itoa.h>

#include <libc-internal.h>
#include <dso_handle.h>

#include <libio/iolibio.h>
#define setvbuf(s, b, f, l) _IO_setvbuf (s, b, f, l)
#define fwrite(buf, size, count, fp) _IO_fwrite (buf, size, count, fp)

#include <kernel-features.h>

#define TRACE_BUFFER_SIZE 512

static FILE *mallstream;
static const char mallenv[] = "MALLOC_TRACE";
static char *malloc_trace_buffer;

__libc_lock_define_initialized (static, lock);

#if SHLIB_COMPAT (libc, GLIBC_2_0, GLIBC_2_34)
/* Compatibility symbols that were introduced to help break at allocation sites
   for specific memory allocations.  This is unusable with ASLR, although gdb
   may allow predictable allocation addresses.  Even then, gdb has watchpoint
   and conditional breakpoint support which should provide the same
   functionality without having this kludge.  These symbols are preserved in
   case some applications ended up linking against them but they don't actually
   do anything anymore; not that they did much before anyway.  */

void *mallwatch __attribute__ ((nocommon));
compat_symbol (libc, mallwatch, mallwatch, GLIBC_2_0);

void
tr_break (void)
{
}
compat_symbol (libc, tr_break, tr_break, GLIBC_2_0);
#endif


/* Old hook values.  */
static void (*tr_old_free_hook) (void *ptr, const void *);
static void *(*tr_old_malloc_hook) (size_t size, const void *);
static void *(*tr_old_realloc_hook) (void *ptr, size_t size,
				     const void *);
static void *(*tr_old_memalign_hook) (size_t __alignment, size_t __size,
				      const void *);

static void
tr_where (const void *caller, Dl_info *info)
{
  if (caller != NULL)
    {
      if (info != NULL)
        {
          char *buf = (char *) "";
          if (info->dli_sname != NULL)
            {
              size_t len = strlen (info->dli_sname);
              buf = alloca (len + 6 + 2 * sizeof (void *));

              buf[0] = '(';
              __stpcpy (_fitoa (caller >= (const void *) info->dli_saddr
                                ? caller - (const void *) info->dli_saddr
                                : (const void *) info->dli_saddr - caller,
                                __stpcpy (__mempcpy (buf + 1, info->dli_sname,
                                                     len),
                                          caller >= (void *) info->dli_saddr
                                          ? "+0x" : "-0x"),
                                16, 0),
                        ")");
            }

          fprintf (mallstream, "@ %s%s%s[%p] ",
                   info->dli_fname ? : "", info->dli_fname ? ":" : "",
                   buf, caller);
        }
      else
        fprintf (mallstream, "@ [%p] ", caller);
    }
}

static Dl_info *
lock_and_info (const void *caller, Dl_info *mem)
{
  if (caller == NULL)
    return NULL;

  Dl_info *res = _dl_addr (caller, mem, NULL, NULL) ? mem : NULL;

  __libc_lock_lock (lock);

  return res;
}

static void tr_freehook (void *, const void *);
static void * tr_mallochook (size_t, const void *);
static void * tr_reallochook (void *, size_t, const void *);
static void * tr_memalignhook (size_t, size_t, const void *);

/* Set all the default non-trace hooks.  */
static __always_inline void
set_default_hooks (void)
{
  __free_hook = tr_old_free_hook;
  __malloc_hook = tr_old_malloc_hook;
  __realloc_hook = tr_old_realloc_hook;
  __memalign_hook = tr_old_memalign_hook;
}

/* Set all of the tracing hooks used for mtrace.  */
static __always_inline void
set_trace_hooks (void)
{
  __free_hook = tr_freehook;
  __malloc_hook = tr_mallochook;
  __realloc_hook = tr_reallochook;
  __memalign_hook = tr_memalignhook;
}

/* Save the current set of hooks as the default hooks.  */
static __always_inline void
save_default_hooks (void)
{
  tr_old_free_hook = __free_hook;
  tr_old_malloc_hook = __malloc_hook;
  tr_old_realloc_hook = __realloc_hook;
  tr_old_memalign_hook = __memalign_hook;
}

static void
tr_freehook (void *ptr, const void *caller)
{
  if (ptr == NULL)
    return;

  Dl_info mem;
  Dl_info *info = lock_and_info (caller, &mem);
  tr_where (caller, info);
  /* Be sure to print it first.  */
  fprintf (mallstream, "- %p\n", ptr);
  set_default_hooks ();
  if (tr_old_free_hook != NULL)
    (*tr_old_free_hook)(ptr, caller);
  else
    free (ptr);
  set_trace_hooks ();
  __libc_lock_unlock (lock);
}

static void *
tr_mallochook (size_t size, const void *caller)
{
  void *hdr;

  Dl_info mem;
  Dl_info *info = lock_and_info (caller, &mem);

  set_default_hooks ();
  if (tr_old_malloc_hook != NULL)
    hdr = (void *) (*tr_old_malloc_hook)(size, caller);
  else
    hdr = (void *) malloc (size);
  set_trace_hooks ();

  tr_where (caller, info);
  /* We could be printing a NULL here; that's OK.  */
  fprintf (mallstream, "+ %p %#lx\n", hdr, (unsigned long int) size);

  __libc_lock_unlock (lock);

  return hdr;
}

static void *
tr_reallochook (void *ptr, size_t size, const void *caller)
{
  void *hdr;

  Dl_info mem;
  Dl_info *info = lock_and_info (caller, &mem);

  set_default_hooks ();
  if (tr_old_realloc_hook != NULL)
    hdr = (void *) (*tr_old_realloc_hook)(ptr, size, caller);
  else
    hdr = (void *) realloc (ptr, size);
  set_trace_hooks ();

  tr_where (caller, info);
  if (hdr == NULL)
    {
      if (size != 0)
        /* Failed realloc.  */
        fprintf (mallstream, "! %p %#lx\n", ptr, (unsigned long int) size);
      else
        fprintf (mallstream, "- %p\n", ptr);
    }
  else if (ptr == NULL)
    fprintf (mallstream, "+ %p %#lx\n", hdr, (unsigned long int) size);
  else
    {
      fprintf (mallstream, "< %p\n", ptr);
      tr_where (caller, info);
      fprintf (mallstream, "> %p %#lx\n", hdr, (unsigned long int) size);
    }

  __libc_lock_unlock (lock);

  return hdr;
}

static void *
tr_memalignhook (size_t alignment, size_t size, const void *caller)
{
  void *hdr;

  Dl_info mem;
  Dl_info *info = lock_and_info (caller, &mem);

  set_default_hooks ();
  if (tr_old_memalign_hook != NULL)
    hdr = (void *) (*tr_old_memalign_hook)(alignment, size, caller);
  else
    hdr = (void *) memalign (alignment, size);
  set_trace_hooks ();

  tr_where (caller, info);
  /* We could be printing a NULL here; that's OK.  */
  fprintf (mallstream, "+ %p %#lx\n", hdr, (unsigned long int) size);

  __libc_lock_unlock (lock);

  return hdr;
}


#ifdef _LIBC

/* This function gets called to make sure all memory the library
   allocates get freed and so does not irritate the user when studying
   the mtrace output.  */
static void __libc_freeres_fn_section
release_libc_mem (void)
{
  /* Only call the free function if we still are running in mtrace mode.  */
  if (mallstream != NULL)
    __libc_freeres ();
}
#endif


/* We enable tracing if the environment variable MALLOC_TRACE is set.  */

void
mtrace (void)
{
#ifdef _LIBC
  static int added_atexit_handler;
#endif
  char *mallfile;

  /* Don't panic if we're called more than once.  */
  if (mallstream != NULL)
    return;

#ifdef _LIBC
  /* When compiling the GNU libc we use the secure getenv function
     which prevents the misuse in case of SUID or SGID enabled
     programs.  */
  mallfile = __libc_secure_getenv (mallenv);
#else
  mallfile = getenv (mallenv);
#endif
  if (mallfile != NULL)
    {
      char *mtb = malloc (TRACE_BUFFER_SIZE);
      if (mtb == NULL)
        return;

      mallstream = fopen (mallfile != NULL ? mallfile : "/dev/null", "wce");
      if (mallstream != NULL)
        {
          /* Be sure it doesn't malloc its buffer!  */
          malloc_trace_buffer = mtb;
          setvbuf (mallstream, malloc_trace_buffer, _IOFBF, TRACE_BUFFER_SIZE);
          fprintf (mallstream, "= Start\n");
	  save_default_hooks ();
	  set_trace_hooks ();
#ifdef _LIBC
          if (!added_atexit_handler)
            {
              added_atexit_handler = 1;
              __cxa_atexit ((void (*)(void *))release_libc_mem, NULL,
			    __dso_handle);
            }
#endif
        }
      else
        free (mtb);
    }
}

void
muntrace (void)
{
  if (mallstream == NULL)
    return;

  /* Do the reverse of what done in mtrace: first reset the hooks and
     MALLSTREAM, and only after that write the trailer and close the
     file.  */
  FILE *f = mallstream;
  mallstream = NULL;
  set_default_hooks ();

  fprintf (f, "= End\n");
  fclose (f);
}