osprey/cygnus/bfd/hash.c

Go to the documentation of this file.

/*
 * Copyright 2003, 2004, 2005, 2006 PathScale, Inc.  All Rights Reserved.
 */

/* hash.c -- hash table routines for BFD
   Copyright 1993, 1994, 1995, 1997, 1999, 2001, 2002, 2003, 2004
   Free Software Foundation, Inc.
   Written by Steve Chamberlain <sac@cygnus.com>

   This file is part of BFD, the Binary File Descriptor library.

   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 of the License, 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.  */

#include "bfd.h"
#include "sysdep.h"
#include "libbfd.h"
#include "objalloc.h"
#include "libiberty.h"

/*
SECTION
  Hash Tables

@cindex Hash tables
  BFD provides a simple set of hash table functions.  Routines
  are provided to initialize a hash table, to free a hash table,
  to look up a string in a hash table and optionally create an
  entry for it, and to traverse a hash table.  There is
  currently no routine to delete an string from a hash table.

  The basic hash table does not permit any data to be stored
  with a string.  However, a hash table is designed to present a
  base class from which other types of hash tables may be
  derived.  These derived types may store additional information
  with the string.  Hash tables were implemented in this way,
  rather than simply providing a data pointer in a hash table
  entry, because they were designed for use by the linker back
  ends.  The linker may create thousands of hash table entries,
  and the overhead of allocating private data and storing and
  following pointers becomes noticeable.

  The basic hash table code is in <<hash.c>>.

@menu
@* Creating and Freeing a Hash Table::
@* Looking Up or Entering a String::
@* Traversing a Hash Table::
@* Deriving a New Hash Table Type::
@end menu

INODE
Creating and Freeing a Hash Table, Looking Up or Entering a String, Hash Tables, Hash Tables
SUBSECTION
  Creating and freeing a hash table

@findex bfd_hash_table_init
@findex bfd_hash_table_init_n
  To create a hash table, create an instance of a <<struct
  bfd_hash_table>> (defined in <<bfd.h>>) and call
  <<bfd_hash_table_init>> (if you know approximately how many
  entries you will need, the function <<bfd_hash_table_init_n>>,
  which takes a @var{size} argument, may be used).
  <<bfd_hash_table_init>> returns <<FALSE>> if some sort of
  error occurs.

@findex bfd_hash_newfunc
  The function <<bfd_hash_table_init>> take as an argument a
  function to use to create new entries.  For a basic hash
  table, use the function <<bfd_hash_newfunc>>.  @xref{Deriving
  a New Hash Table Type}, for why you would want to use a
  different value for this argument.

@findex bfd_hash_allocate
  <<bfd_hash_table_init>> will create an objalloc which will be
  used to allocate new entries.  You may allocate memory on this
  objalloc using <<bfd_hash_allocate>>.

@findex bfd_hash_table_free
  Use <<bfd_hash_table_free>> to free up all the memory that has
  been allocated for a hash table.  This will not free up the
  <<struct bfd_hash_table>> itself, which you must provide.

@findex bfd_hash_set_default_size
  Use <<bfd_hash_set_default_size>> to set the default size of
  hash table to use.

INODE
Looking Up or Entering a String, Traversing a Hash Table, Creating and Freeing a Hash Table, Hash Tables
SUBSECTION
  Looking up or entering a string

@findex bfd_hash_lookup
  The function <<bfd_hash_lookup>> is used both to look up a
  string in the hash table and to create a new entry.

  If the @var{create} argument is <<FALSE>>, <<bfd_hash_lookup>>
  will look up a string.  If the string is found, it will
  returns a pointer to a <<struct bfd_hash_entry>>.  If the
  string is not found in the table <<bfd_hash_lookup>> will
  return <<NULL>>.  You should not modify any of the fields in
  the returns <<struct bfd_hash_entry>>.

  If the @var{create} argument is <<TRUE>>, the string will be
  entered into the hash table if it is not already there.
  Either way a pointer to a <<struct bfd_hash_entry>> will be
  returned, either to the existing structure or to a newly
  created one.  In this case, a <<NULL>> return means that an
  error occurred.

  If the @var{create} argument is <<TRUE>>, and a new entry is
  created, the @var{copy} argument is used to decide whether to
  copy the string onto the hash table objalloc or not.  If
  @var{copy} is passed as <<FALSE>>, you must be careful not to
  deallocate or modify the string as long as the hash table
  exists.

INODE
Traversing a Hash Table, Deriving a New Hash Table Type, Looking Up or Entering a String, Hash Tables
SUBSECTION
  Traversing a hash table

@findex bfd_hash_traverse
  The function <<bfd_hash_traverse>> may be used to traverse a
  hash table, calling a function on each element.  The traversal
  is done in a random order.

  <<bfd_hash_traverse>> takes as arguments a function and a
  generic <<void *>> pointer.  The function is called with a
  hash table entry (a <<struct bfd_hash_entry *>>) and the
  generic pointer passed to <<bfd_hash_traverse>>.  The function
  must return a <<boolean>> value, which indicates whether to
  continue traversing the hash table.  If the function returns
  <<FALSE>>, <<bfd_hash_traverse>> will stop the traversal and
  return immediately.

INODE
Deriving a New Hash Table Type, , Traversing a Hash Table, Hash Tables
SUBSECTION
  Deriving a new hash table type

  Many uses of hash tables want to store additional information
  which each entry in the hash table.  Some also find it
  convenient to store additional information with the hash table
  itself.  This may be done using a derived hash table.

  Since C is not an object oriented language, creating a derived
  hash table requires sticking together some boilerplate
  routines with a few differences specific to the type of hash
  table you want to create.

  An example of a derived hash table is the linker hash table.
  The structures for this are defined in <<bfdlink.h>>.  The
  functions are in <<linker.c>>.

  You may also derive a hash table from an already derived hash
  table.  For example, the a.out linker backend code uses a hash
  table derived from the linker hash table.

@menu
@* Define the Derived Structures::
@* Write the Derived Creation Routine::
@* Write Other Derived Routines::
@end menu

INODE
Define the Derived Structures, Write the Derived Creation Routine, Deriving a New Hash Table Type, Deriving a New Hash Table Type
SUBSUBSECTION
  Define the derived structures

  You must define a structure for an entry in the hash table,
  and a structure for the hash table itself.

  The first field in the structure for an entry in the hash
  table must be of the type used for an entry in the hash table
  you are deriving from.  If you are deriving from a basic hash
  table this is <<struct bfd_hash_entry>>, which is defined in
  <<bfd.h>>.  The first field in the structure for the hash
  table itself must be of the type of the hash table you are
  deriving from itself.  If you are deriving from a basic hash
  table, this is <<struct bfd_hash_table>>.

  For example, the linker hash table defines <<struct
  bfd_link_hash_entry>> (in <<bfdlink.h>>).  The first field,
  <<root>>, is of type <<struct bfd_hash_entry>>.  Similarly,
  the first field in <<struct bfd_link_hash_table>>, <<table>>,
  is of type <<struct bfd_hash_table>>.

INODE
Write the Derived Creation Routine, Write Other Derived Routines, Define the Derived Structures, Deriving a New Hash Table Type
SUBSUBSECTION
  Write the derived creation routine

  You must write a routine which will create and initialize an
  entry in the hash table.  This routine is passed as the
  function argument to <<bfd_hash_table_init>>.

  In order to permit other hash tables to be derived from the
  hash table you are creating, this routine must be written in a
  standard way.

  The first argument to the creation routine is a pointer to a
  hash table entry.  This may be <<NULL>>, in which case the
  routine should allocate the right amount of space.  Otherwise
  the space has already been allocated by a hash table type
  derived from this one.

  After allocating space, the creation routine must call the
  creation routine of the hash table type it is derived from,
  passing in a pointer to the space it just allocated.  This
  will initialize any fields used by the base hash table.

  Finally the creation routine must initialize any local fields
  for the new hash table type.

  Here is a boilerplate example of a creation routine.
  @var{function_name} is the name of the routine.
  @var{entry_type} is the type of an entry in the hash table you
  are creating.  @var{base_newfunc} is the name of the creation
  routine of the hash table type your hash table is derived
  from.

EXAMPLE

.struct bfd_hash_entry *
.@var{function_name} (entry, table, string)
.     struct bfd_hash_entry *entry;
.     struct bfd_hash_table *table;
.     const char *string;
.{
.  struct @var{entry_type} *ret = (@var{entry_type} *) entry;
.
. {* Allocate the structure if it has not already been allocated by a
.    derived class.  *}
.  if (ret == (@var{entry_type} *) NULL)
.    {
.      ret = ((@var{entry_type} *)
.       bfd_hash_allocate (table, sizeof (@var{entry_type})));
.      if (ret == (@var{entry_type} *) NULL)
.        return NULL;
.    }
.
. {* Call the allocation method of the base class.  *}
.  ret = ((@var{entry_type} *)
.  @var{base_newfunc} ((struct bfd_hash_entry *) ret, table, string));
.
. {* Initialize the local fields here.  *}
.
.  return (struct bfd_hash_entry *) ret;
.}

DESCRIPTION
  The creation routine for the linker hash table, which is in
  <<linker.c>>, looks just like this example.
  @var{function_name} is <<_bfd_link_hash_newfunc>>.
  @var{entry_type} is <<struct bfd_link_hash_entry>>.
  @var{base_newfunc} is <<bfd_hash_newfunc>>, the creation
  routine for a basic hash table.

  <<_bfd_link_hash_newfunc>> also initializes the local fields
  in a linker hash table entry: <<type>>, <<written>> and
  <<next>>.

INODE
Write Other Derived Routines, , Write the Derived Creation Routine, Deriving a New Hash Table Type
SUBSUBSECTION
  Write other derived routines

  You will want to write other routines for your new hash table,
  as well.

  You will want an initialization routine which calls the
  initialization routine of the hash table you are deriving from
  and initializes any other local fields.  For the linker hash
  table, this is <<_bfd_link_hash_table_init>> in <<linker.c>>.

  You will want a lookup routine which calls the lookup routine
  of the hash table you are deriving from and casts the result.
  The linker hash table uses <<bfd_link_hash_lookup>> in
  <<linker.c>> (this actually takes an additional argument which
  it uses to decide how to return the looked up value).

  You may want a traversal routine.  This should just call the
  traversal routine of the hash table you are deriving from with
  appropriate casts.  The linker hash table uses
  <<bfd_link_hash_traverse>> in <<linker.c>>.

  These routines may simply be defined as macros.  For example,
  the a.out backend linker hash table, which is derived from the
  linker hash table, uses macros for the lookup and traversal
  routines.  These are <<aout_link_hash_lookup>> and
  <<aout_link_hash_traverse>> in aoutx.h.
*/

/* The default number of entries to use when creating a hash table.  */
#define DEFAULT_SIZE 4051
static size_t bfd_default_hash_table_size = DEFAULT_SIZE;

/* Create a new hash table, given a number of entries.  */

bfd_boolean
bfd_hash_table_init_n (table, newfunc, size)
     struct bfd_hash_table *table;
     struct bfd_hash_entry *(*newfunc) PARAMS ((struct bfd_hash_entry *,
            struct bfd_hash_table *,
            const char *));
     unsigned int size;
{
  unsigned int alloc;

  alloc = size * sizeof (struct bfd_hash_entry *);

  table->memory = (PTR) objalloc_create ();
  if (table->memory == NULL)
    {
      bfd_set_error (bfd_error_no_memory);
      return FALSE;
    }
  table->table = ((struct bfd_hash_entry **)
      objalloc_alloc ((struct objalloc *) table->memory, alloc));
  if (table->table == NULL)
    {
      bfd_set_error (bfd_error_no_memory);
      return FALSE;
    }
  memset ((PTR) table->table, 0, alloc);
  table->size = size;
  table->newfunc = newfunc;
  return TRUE;
}

/* Create a new hash table with the default number of entries.  */

bfd_boolean
bfd_hash_table_init (table, newfunc)
     struct bfd_hash_table *table;
     struct bfd_hash_entry *(*newfunc) PARAMS ((struct bfd_hash_entry *,
            struct bfd_hash_table *,
            const char *));
{
  return bfd_hash_table_init_n (table, newfunc, bfd_default_hash_table_size);
}

/* Free a hash table.  */

void
bfd_hash_table_free (table)
     struct bfd_hash_table *table;
{
  objalloc_free ((struct objalloc *) table->memory);
  table->memory = NULL;
}

/* Look up a string in a hash table.  */

struct bfd_hash_entry *
bfd_hash_lookup (table, string, create, copy)
     struct bfd_hash_table *table;
     const char *string;
     bfd_boolean create;
     bfd_boolean copy;
{
  register const unsigned char *s;
  register unsigned long hash;
  register unsigned int c;
  struct bfd_hash_entry *hashp;
  unsigned int len;
  unsigned int index;

  hash = 0;
  len = 0;
  s = (const unsigned char *) string;
  while ((c = *s++) != '\0')
    {
      hash += c + (c << 17);
      hash ^= hash >> 2;
    }
  len = (s - (const unsigned char *) string) - 1;
  hash += len + (len << 17);
  hash ^= hash >> 2;

  index = hash % table->size;
  for (hashp = table->table[index];
       hashp != (struct bfd_hash_entry *) NULL;
       hashp = hashp->next)
    {
      if (hashp->hash == hash
    && strcmp (hashp->string, string) == 0)
  return hashp;
    }

  if (! create)
    return (struct bfd_hash_entry *) NULL;

  hashp = (*table->newfunc) ((struct bfd_hash_entry *) NULL, table, string);
  if (hashp == (struct bfd_hash_entry *) NULL)
    return (struct bfd_hash_entry *) NULL;
  if (copy)
    {
      char *new;

      new = (char *) objalloc_alloc ((struct objalloc *) table->memory,
             len + 1);
      if (!new)
  {
    bfd_set_error (bfd_error_no_memory);
    return (struct bfd_hash_entry *) NULL;
  }
      memcpy (new, string, len + 1);
      string = new;
    }
  hashp->string = string;
  hashp->hash = hash;
  hashp->next = table->table[index];
  table->table[index] = hashp;

  return hashp;
}

/* Replace an entry in a hash table.  */

void
bfd_hash_replace (table, old, nw)
     struct bfd_hash_table *table;
     struct bfd_hash_entry *old;
     struct bfd_hash_entry *nw;
{
  unsigned int index;
  struct bfd_hash_entry **pph;

  index = old->hash % table->size;
  for (pph = &table->table[index];
       (*pph) != (struct bfd_hash_entry *) NULL;
       pph = &(*pph)->next)
    {
      if (*pph == old)
  {
    *pph = nw;
    return;
  }
    }

  abort ();
}

/* Base method for creating a new hash table entry.  */

struct bfd_hash_entry *
bfd_hash_newfunc (entry, table, string)
     struct bfd_hash_entry *entry;
     struct bfd_hash_table *table;
     const char *string ATTRIBUTE_UNUSED;
{
  if (entry == (struct bfd_hash_entry *) NULL)
    entry = ((struct bfd_hash_entry *)
       bfd_hash_allocate (table, sizeof (struct bfd_hash_entry)));
  return entry;
}

/* Allocate space in a hash table.  */

PTR
bfd_hash_allocate (table, size)
     struct bfd_hash_table *table;
     unsigned int size;
{
  PTR ret;

  ret = objalloc_alloc ((struct objalloc *) table->memory, size);
  if (ret == NULL && size != 0)
    bfd_set_error (bfd_error_no_memory);
#ifdef KEY
  memset (ret, 0, size);  // For section_is_invalid.
#endif
  return ret;
}

/* Traverse a hash table.  */

void
bfd_hash_traverse (table, func, info)
     struct bfd_hash_table *table;
     bfd_boolean (*func) PARAMS ((struct bfd_hash_entry *, PTR));
     PTR info;
{
  unsigned int i;

  for (i = 0; i < table->size; i++)
    {
      struct bfd_hash_entry *p;

      for (p = table->table[i]; p != NULL; p = p->next)
  {
    if (! (*func) (p, info))
      return;
  }
    }
}

void
bfd_hash_set_default_size (bfd_size_type hash_size)
{
  /* Extend this prime list if you want more granularity of hash table size.  */
  static const bfd_size_type hash_size_primes[] =
    {
      1021, 4051, 8599, 16699
    };
  size_t index;

  /* Work out best prime number near the hash_size.  */
  for (index = 0; index < ARRAY_SIZE (hash_size_primes) - 1; ++index)
    if (hash_size <= hash_size_primes[index])
      break;

  bfd_default_hash_table_size = hash_size_primes[index];
}

/* A few different object file formats (a.out, COFF, ELF) use a string
   table.  These functions support adding strings to a string table,
   returning the byte offset, and writing out the table.

   Possible improvements:
   + look for strings matching trailing substrings of other strings
   + better data structures?  balanced trees?
   + look at reducing memory use elsewhere -- maybe if we didn't have
     to construct the entire symbol table at once, we could get by
     with smaller amounts of VM?  (What effect does that have on the
     string table reductions?)  */

/* An entry in the strtab hash table.  */

struct strtab_hash_entry
{
  struct bfd_hash_entry root;
  /* Index in string table.  */
  bfd_size_type index;
  /* Next string in strtab.  */
  struct strtab_hash_entry *next;
};

/* The strtab hash table.  */

struct bfd_strtab_hash
{
  struct bfd_hash_table table;
  /* Size of strtab--also next available index.  */
  bfd_size_type size;
  /* First string in strtab.  */
  struct strtab_hash_entry *first;
  /* Last string in strtab.  */
  struct strtab_hash_entry *last;
  /* Whether to precede strings with a two byte length, as in the
     XCOFF .debug section.  */
  bfd_boolean xcoff;
};

static struct bfd_hash_entry *strtab_hash_newfunc
  PARAMS ((struct bfd_hash_entry *, struct bfd_hash_table *, const char *));

/* Routine to create an entry in a strtab.  */

static struct bfd_hash_entry *
strtab_hash_newfunc (entry, table, string)
     struct bfd_hash_entry *entry;
     struct bfd_hash_table *table;
     const char *string;
{
  struct strtab_hash_entry *ret = (struct strtab_hash_entry *) entry;

  /* Allocate the structure if it has not already been allocated by a
     subclass.  */
  if (ret == (struct strtab_hash_entry *) NULL)
    ret = ((struct strtab_hash_entry *)
     bfd_hash_allocate (table, sizeof (struct strtab_hash_entry)));
  if (ret == (struct strtab_hash_entry *) NULL)
    return NULL;

  /* Call the allocation method of the superclass.  */
  ret = ((struct strtab_hash_entry *)
   bfd_hash_newfunc ((struct bfd_hash_entry *) ret, table, string));

  if (ret)
    {
      /* Initialize the local fields.  */
      ret->index = (bfd_size_type) -1;
      ret->next = NULL;
    }

  return (struct bfd_hash_entry *) ret;
}

/* Look up an entry in an strtab.  */

#define strtab_hash_lookup(t, string, create, copy) \
  ((struct strtab_hash_entry *) \
   bfd_hash_lookup (&(t)->table, (string), (create), (copy)))

/* Create a new strtab.  */

struct bfd_strtab_hash *
_bfd_stringtab_init ()
{
  struct bfd_strtab_hash *table;
  bfd_size_type amt = sizeof (struct bfd_strtab_hash);

  table = (struct bfd_strtab_hash *) bfd_malloc (amt);
  if (table == NULL)
    return NULL;

  if (! bfd_hash_table_init (&table->table, strtab_hash_newfunc))
    {
      free (table);
      return NULL;
    }

  table->size = 0;
  table->first = NULL;
  table->last = NULL;
  table->xcoff = FALSE;

  return table;
}

/* Create a new strtab in which the strings are output in the format
   used in the XCOFF .debug section: a two byte length precedes each
   string.  */

struct bfd_strtab_hash *
_bfd_xcoff_stringtab_init ()
{
  struct bfd_strtab_hash *ret;

  ret = _bfd_stringtab_init ();
  if (ret != NULL)
    ret->xcoff = TRUE;
  return ret;
}

/* Free a strtab.  */

void
_bfd_stringtab_free (table)
     struct bfd_strtab_hash *table;
{
  bfd_hash_table_free (&table->table);
  free (table);
}

/* Get the index of a string in a strtab, adding it if it is not
   already present.  If HASH is FALSE, we don't really use the hash
   table, and we don't eliminate duplicate strings.  */

bfd_size_type
_bfd_stringtab_add (tab, str, hash, copy)
     struct bfd_strtab_hash *tab;
     const char *str;
     bfd_boolean hash;
     bfd_boolean copy;
{
  register struct strtab_hash_entry *entry;

  if (hash)
    {
      entry = strtab_hash_lookup (tab, str, TRUE, copy);
      if (entry == NULL)
  return (bfd_size_type) -1;
    }
  else
    {
      entry = ((struct strtab_hash_entry *)
         bfd_hash_allocate (&tab->table,
          sizeof (struct strtab_hash_entry)));
      if (entry == NULL)
  return (bfd_size_type) -1;
      if (! copy)
  entry->root.string = str;
      else
  {
    char *n;

    n = (char *) bfd_hash_allocate (&tab->table, strlen (str) + 1);
    if (n == NULL)
      return (bfd_size_type) -1;
    entry->root.string = n;
  }
      entry->index = (bfd_size_type) -1;
      entry->next = NULL;
    }

  if (entry->index == (bfd_size_type) -1)
    {
      entry->index = tab->size;
      tab->size += strlen (str) + 1;
      if (tab->xcoff)
  {
    entry->index += 2;
    tab->size += 2;
  }
      if (tab->first == NULL)
  tab->first = entry;
      else
  tab->last->next = entry;
      tab->last = entry;
    }

  return entry->index;
}

/* Get the number of bytes in a strtab.  */

bfd_size_type
_bfd_stringtab_size (tab)
     struct bfd_strtab_hash *tab;
{
  return tab->size;
}

/* Write out a strtab.  ABFD must already be at the right location in
   the file.  */

bfd_boolean
_bfd_stringtab_emit (abfd, tab)
     register bfd *abfd;
     struct bfd_strtab_hash *tab;
{
  register bfd_boolean xcoff;
  register struct strtab_hash_entry *entry;

  xcoff = tab->xcoff;

  for (entry = tab->first; entry != NULL; entry = entry->next)
    {
      const char *str;
      size_t len;

      str = entry->root.string;
      len = strlen (str) + 1;

      if (xcoff)
  {
    bfd_byte buf[2];

    /* The output length includes the null byte.  */
    bfd_put_16 (abfd, (bfd_vma) len, buf);
    if (bfd_bwrite ((PTR) buf, (bfd_size_type) 2, abfd) != 2)
      return FALSE;
  }

      if (bfd_bwrite ((PTR) str, (bfd_size_type) len, abfd) != len)
  return FALSE;
    }

  return TRUE;
}

---