[deliverable/binutils-gdb.git] / ld / plugin.c

/* Plugin control for the GNU linker.
   Copyright 2010 Free Software Foundation, Inc.

   This file is part of the GNU Binutils.

   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 3 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., 51 Franklin Street - Fifth Floor, Boston,
   MA 02110-1301, USA.  */

#include "sysdep.h"
#include "libiberty.h"
#include "bfd.h"
#include "bfdlink.h"
#include "bfdver.h"
#include "ld.h"
#include "ldmain.h"
#include "ldmisc.h"
#include "ldexp.h"
#include "ldlang.h"
#include "ldfile.h"
#include "plugin.h"
#include "plugin-api.h"
#include "elf-bfd.h"
#if !defined (HAVE_DLFCN_H) && defined (HAVE_WINDOWS_H)
#include <Windows.h>
#endif

/* The suffix to append to the name of the real (claimed) object file
   when generating a dummy BFD to hold the IR symbols sent from the
   plugin.  */
#define IRONLY_SUFFIX           ".ironly\004"

/* This is sizeof an array of chars, not sizeof a const char *.  We
   also have to avoid inadvertently counting the trailing NUL.  */
#define IRONLY_SUFFIX_LEN       (sizeof (IRONLY_SUFFIX) - 1)

/* Stores a single argument passed to a plugin.  */
typedef struct plugin_arg
{
  struct plugin_arg *next;
  const char *arg;
} plugin_arg_t;

/* Holds all details of a single plugin.  */
typedef struct plugin
{
  /* Next on the list of plugins, or NULL at end of chain.  */
  struct plugin *next;
  /* The argument string given to --plugin.  */
  const char *name;
  /* The shared library handle returned by dlopen.  */
  void *dlhandle;
  /* The list of argument string given to --plugin-opt.  */
  plugin_arg_t *args;
  /* Number of args in the list, for convenience.  */
  size_t n_args;
  /* The plugin's event handlers.  */
  ld_plugin_claim_file_handler claim_file_handler;
  ld_plugin_all_symbols_read_handler all_symbols_read_handler;
  ld_plugin_cleanup_handler cleanup_handler;
  /* TRUE if the cleanup handlers have been called.  */
  bfd_boolean cleanup_done;
} plugin_t;

/* The master list of all plugins.  */
static plugin_t *plugins_list = NULL;

/* We keep a tail pointer for easy linking on the end.  */
static plugin_t **plugins_tail_chain_ptr = &plugins_list;

/* The last plugin added to the list, for receiving args.  */
static plugin_t *last_plugin = NULL;

/* The tail of the arg chain of the last plugin added to the list.  */
static plugin_arg_t **last_plugin_args_tail_chain_ptr = NULL;

/* The plugin which is currently having a callback executed.  */
static plugin_t *called_plugin = NULL;

/* Last plugin to cause an error, if any.  */
static const char *error_plugin = NULL;

/* A hash table that records symbols referenced by non-IR files.  Used
   at get_symbols time to determine whether any prevailing defs from
   IR files are referenced only from other IR files, so tthat we can
   we can distinguish the LDPR_PREVAILING_DEF and LDPR_PREVAILING_DEF_IRONLY
   cases when establishing symbol resolutions.  */
static struct bfd_hash_table *non_ironly_hash = NULL;

/* Set at all symbols read time, to avoid recursively offering the plugin
   its own newly-added input files and libs to claim.  */
static bfd_boolean no_more_claiming = FALSE;

/* If the --allow-multiple-definition command-line option is active, we
   have to disable it so that BFD always calls our hook, and simulate the
   effect (when not resolving IR vs. real symbols) ourselves by ensuring
   TRUE is returned from the hook.  */
static bfd_boolean plugin_cached_allow_multiple_defs = FALSE;

/* List of tags to set in the constant leading part of the tv array. */
static const enum ld_plugin_tag tv_header_tags[] =
{
  LDPT_MESSAGE,
  LDPT_API_VERSION,
  LDPT_GNU_LD_VERSION,
  LDPT_LINKER_OUTPUT,
  LDPT_OUTPUT_NAME,
  LDPT_REGISTER_CLAIM_FILE_HOOK,
  LDPT_REGISTER_ALL_SYMBOLS_READ_HOOK,
  LDPT_REGISTER_CLEANUP_HOOK,
  LDPT_ADD_SYMBOLS,
  LDPT_GET_INPUT_FILE,
  LDPT_RELEASE_INPUT_FILE,
  LDPT_GET_SYMBOLS,
  LDPT_ADD_INPUT_FILE,
  LDPT_ADD_INPUT_LIBRARY,
  LDPT_SET_EXTRA_LIBRARY_PATH
};

/* How many entries in the constant leading part of the tv array.  */
static const size_t tv_header_size = ARRAY_SIZE (tv_header_tags);

#if !defined (HAVE_DLFCN_H) && defined (HAVE_WINDOWS_H)

#define RTLD_NOW 0      /* Dummy value.  */

static void *
dlopen (const char *file, int mode ATTRIBUTE_UNUSED)
{
  return LoadLibrary (file);
}

static void *
dlsym (void *handle, const char *name)
{
  return GetProcAddress (handle, name);
}

static int
dlclose (void *handle)
{
  FreeLibrary (handle);
  return 0;
}

#endif /* !defined (HAVE_DLFCN_H) && defined (HAVE_WINDOWS_H)  */

/* Helper function for exiting with error status.  */
static int
set_plugin_error (const char *plugin)
{
  error_plugin = plugin;
  return -1;
}

/* Test if an error occurred.  */
static bfd_boolean
plugin_error_p (void)
{
  return error_plugin != NULL;
}

/* Return name of plugin which caused an error if any.  */
const char *plugin_error_plugin (void)
{
  return error_plugin ? error_plugin : _("<no plugin>");
}

/* Handle -plugin arg: find and load plugin, or return error.  */
int plugin_opt_plugin (const char *plugin)
{
  plugin_t *newplug;

  newplug = xmalloc (sizeof *newplug);
  memset (newplug, 0, sizeof *newplug);
  newplug->name = plugin;
  newplug->dlhandle = dlopen (plugin, RTLD_NOW);
  if (!newplug->dlhandle)
    return set_plugin_error (plugin);

  /* Chain on end, so when we run list it is in command-line order.  */
  *plugins_tail_chain_ptr = newplug;
  plugins_tail_chain_ptr = &newplug->next;

  /* Record it as current plugin for receiving args.  */
  last_plugin = newplug;
  last_plugin_args_tail_chain_ptr = &newplug->args;
  return 0;
}

/* Accumulate option arguments for last-loaded plugin, or return
   error if none.  */
int plugin_opt_plugin_arg (const char *arg)
{
  plugin_arg_t *newarg;

  if (!last_plugin)
    return set_plugin_error (_("<no plugin>"));

  newarg = xmalloc (sizeof *newarg);
  newarg->arg = arg;
  newarg->next = NULL;

  /* Chain on end to preserve command-line order.  */
  *last_plugin_args_tail_chain_ptr = newarg;
  last_plugin_args_tail_chain_ptr = &newarg->next;
  last_plugin->n_args++;
  return 0;
}

/* Create a dummy BFD.  */
bfd *
plugin_get_ir_dummy_bfd (const char *name, bfd *srctemplate)
{
  asection *sec;
  bfd *abfd;

  bfd_use_reserved_id = 1;
  abfd = bfd_create (concat (name, IRONLY_SUFFIX, (const char *)NULL),
                     srctemplate);
  bfd_set_arch_info (abfd, bfd_get_arch_info (srctemplate));
  bfd_make_writable (abfd);
  /* Create a minimal set of sections to own the symbols.  */
  sec = bfd_make_section_old_way (abfd, ".text");
  bfd_set_section_flags (abfd, sec,
                         (SEC_CODE | SEC_HAS_CONTENTS | SEC_READONLY
                          | SEC_ALLOC | SEC_LOAD | SEC_KEEP));
  sec->output_section = sec;
  sec->output_offset = 0;
  return abfd;
}

/* Check if the BFD is an IR dummy.  */
bfd_boolean
is_ir_dummy_bfd (const bfd *abfd)
{
  size_t namlen = strlen (abfd->filename);
  if (namlen < IRONLY_SUFFIX_LEN)
    return FALSE;
  return !strcmp (abfd->filename + namlen - IRONLY_SUFFIX_LEN, IRONLY_SUFFIX);
}

/* Helpers to convert between BFD and GOLD symbol formats.  */
static enum ld_plugin_status
asymbol_from_plugin_symbol (bfd *abfd, asymbol *asym,
                                const struct ld_plugin_symbol *ldsym)
{
  flagword flags = BSF_NO_FLAGS;
  struct bfd_section *section;

  asym->the_bfd = abfd;
  asym->name = ldsym->version
                ? concat (ldsym->name, "@", ldsym->version, NULL)
                : ldsym->name;
  asym->value = 0;
  switch (ldsym->def)
    {
    case LDPK_WEAKDEF:
      flags = BSF_WEAK;
      /* FALLTHRU */
    case LDPK_DEF:
      flags |= BSF_GLOBAL;
      section = bfd_get_section_by_name (abfd, ".text");
      break;

    case LDPK_WEAKUNDEF:
      flags = BSF_WEAK;
      /* FALLTHRU */
    case LDPK_UNDEF:
      section = bfd_und_section_ptr;
      break;

    case LDPK_COMMON:
      flags = BSF_GLOBAL;
      section = bfd_com_section_ptr;
      asym->value = ldsym->size;
      break;

    default:
      return LDPS_ERR;
    }
  asym->flags = flags;
  asym->section = section;

  /* Visibility only applies on ELF targets.  */
  if (bfd_get_flavour (abfd) == bfd_target_elf_flavour)
    {
      elf_symbol_type *elfsym = elf_symbol_from (abfd, asym);
      if (!elfsym)
        einfo (_("%P%F: %s: non-ELF symbol in ELF BFD!"), asym->name);
      elfsym->internal_elf_sym.st_other &= ~3;
      elfsym->internal_elf_sym.st_other |= ldsym->visibility;
    }

  return LDPS_OK;
}

/* Register a claim-file handler.  */
static enum ld_plugin_status
register_claim_file (ld_plugin_claim_file_handler handler)
{
  ASSERT (called_plugin);
  called_plugin->claim_file_handler = handler;
  return LDPS_OK;
}

/* Register an all-symbols-read handler.  */
static enum ld_plugin_status
register_all_symbols_read (ld_plugin_all_symbols_read_handler handler)
{
  ASSERT (called_plugin);
  called_plugin->all_symbols_read_handler = handler;
  return LDPS_OK;
}

/* Register a cleanup handler.  */
static enum ld_plugin_status
register_cleanup (ld_plugin_cleanup_handler handler)
{
  ASSERT (called_plugin);
  called_plugin->cleanup_handler = handler;
  return LDPS_OK;
}

/* Add symbols from a plugin-claimed input file.  */
static enum ld_plugin_status
add_symbols (void *handle, int nsyms, const struct ld_plugin_symbol *syms)
{
  asymbol **symptrs;
  bfd *abfd = handle;
  int n;
  ASSERT (called_plugin);
  symptrs = xmalloc (nsyms * sizeof *symptrs);
  for (n = 0; n < nsyms; n++)
    {
      enum ld_plugin_status rv;
      asymbol *bfdsym = bfd_make_empty_symbol (abfd);
      symptrs[n] = bfdsym;
      rv = asymbol_from_plugin_symbol (abfd, bfdsym, syms + n);
      if (rv != LDPS_OK)
        return rv;
    }
  bfd_set_symtab (abfd, symptrs, nsyms);
  return LDPS_OK;
}

/* Get the input file information with an open (possibly re-opened)
   file descriptor.  */
static enum ld_plugin_status
get_input_file (const void *handle, struct ld_plugin_input_file *file)
{
  ASSERT (called_plugin);
  handle = handle;
  file = file;
  return LDPS_ERR;
}

/* Release the input file.  */
static enum ld_plugin_status
release_input_file (const void *handle)
{
  ASSERT (called_plugin);
  handle = handle;
  return LDPS_ERR;
}

/* Get the symbol resolution info for a plugin-claimed input file.  */
static enum ld_plugin_status
get_symbols (const void *handle, int nsyms, struct ld_plugin_symbol *syms)
{
  const bfd *abfd = handle;
  int n;
  ASSERT (called_plugin);
  for (n = 0; n < nsyms; n++)
    {
      struct bfd_link_hash_entry *blhe;
      bfd_boolean ironly;

      blhe = bfd_link_hash_lookup (link_info.hash, syms[n].name,
                                FALSE, FALSE, TRUE);
      if (!blhe)
        {
          syms[n].resolution = LDPR_UNKNOWN;
          continue;
        }

      /* Determine resolution from blhe type and symbol's original type.  */
      if (blhe->type == bfd_link_hash_undefined
                || blhe->type == bfd_link_hash_undefweak)
        {
          syms[n].resolution = LDPR_UNDEF;
          continue;
        }
      if (blhe->type != bfd_link_hash_defined
                && blhe->type != bfd_link_hash_defweak
                && blhe->type != bfd_link_hash_common)
        {
          /* We should not have a new, indirect or warning symbol here.  */
          einfo ("%P%F: %s: plugin symbol table corrupt (sym type %d)",
                called_plugin->name, blhe->type);
        }

      /* We need to know if the sym is referenced from non-IR files.  */
      ironly = !bfd_hash_lookup (non_ironly_hash, syms[n].name, FALSE, FALSE);

      /* If it was originally undefined or common, then it has been
         resolved; determine how.  */
      if (syms[n].def == LDPK_UNDEF || syms[n].def == LDPK_WEAKUNDEF
          || syms[n].def == LDPK_COMMON)
        {
          asection *owner_sec = (blhe->type == bfd_link_hash_common)
                                ? blhe->u.c.p->section
                                : blhe->u.def.section;
          if (owner_sec->owner == link_info.output_bfd)
            syms[n].resolution = LDPR_RESOLVED_EXEC;
          else if (owner_sec->owner == abfd)
            syms[n].resolution = (ironly)
                                ? LDPR_PREVAILING_DEF_IRONLY
                                : LDPR_PREVAILING_DEF;
          else if (is_ir_dummy_bfd (owner_sec->owner))
            syms[n].resolution = LDPR_RESOLVED_IR;
          else if (owner_sec->owner->flags & DYNAMIC)
            syms[n].resolution =  LDPR_RESOLVED_DYN;
          else
            syms[n].resolution = LDPR_RESOLVED_EXEC;
          continue;
        }

      /* Was originally def, or weakdef.  Does it prevail?  If the
         owner is the original dummy bfd that supplied it, then this
         is the definition that has prevailed.  */
      if (blhe->u.def.section->owner == link_info.output_bfd)
        syms[n].resolution = LDPR_PREEMPTED_REG;
      else if (blhe->u.def.section->owner == abfd)
        {
          syms[n].resolution = (ironly)
                                ? LDPR_PREVAILING_DEF_IRONLY
                                : LDPR_PREVAILING_DEF;
          continue;
        }

      /* Was originally def, weakdef, or common, but has been pre-empted.  */
      syms[n].resolution = is_ir_dummy_bfd (blhe->u.def.section->owner)
                                ? LDPR_PREEMPTED_IR
                                : LDPR_PREEMPTED_REG;
    }
  return LDPS_OK;
}

/* Add a new (real) input file generated by a plugin.  */
static enum ld_plugin_status
add_input_file (const char *pathname)
{
  ASSERT (called_plugin);
  if (!lang_add_input_file (xstrdup (pathname), lang_input_file_is_file_enum,
        NULL))
    return LDPS_ERR;
  return LDPS_OK;
}

/* Add a new (real) library required by a plugin.  */
static enum ld_plugin_status
add_input_library (const char *pathname)
{
  ASSERT (called_plugin);
  if (!lang_add_input_file (xstrdup (pathname), lang_input_file_is_l_enum,
        NULL))
    return LDPS_ERR;
  return LDPS_OK;
}

/* Set the extra library path to be used by libraries added via
   add_input_library.  */
static enum ld_plugin_status
set_extra_library_path (const char *path)
{
  ASSERT (called_plugin);
  ldfile_add_library_path (xstrdup (path), FALSE);
  return LDPS_OK;
}

/* Issue a diagnostic message from a plugin.  */
static enum ld_plugin_status
message (int level, const char *format, ...)
{
  va_list args;
  va_start (args, format);

  switch (level)
    {
    case LDPL_INFO:
      vfinfo (stdout, format, args, FALSE);
      break;
    case LDPL_WARNING:
      vfinfo (stdout, format, args, TRUE);
      break;
    case LDPL_FATAL:
    case LDPL_ERROR:
    default:
      {
        char *newfmt = ACONCAT ((level == LDPL_FATAL ? "%F" : "%X",
                                format, NULL));
        vfinfo (stderr, newfmt, args, TRUE);
      }
      break;
    }

  va_end (args);
  return LDPS_OK;
}

/* Helper to size leading part of tv array and set it up. */
static size_t
set_tv_header (struct ld_plugin_tv *tv)
{
  size_t i;

  /* Version info.  */
  static const unsigned int major = (unsigned)(BFD_VERSION / 100000000UL);
  static const unsigned int minor = (unsigned)(BFD_VERSION / 1000000UL) % 100;

  if (!tv)
    return tv_header_size;

  for (i = 0; i < tv_header_size; i++)
    {
      tv[i].tv_tag = tv_header_tags[i];
#define TVU(x) tv[i].tv_u.tv_ ## x
      switch (tv[i].tv_tag)
        {
          case LDPT_MESSAGE:
            TVU(message) = message;
            break;
          case LDPT_API_VERSION:
            TVU(val) = LD_PLUGIN_API_VERSION;
            break;
          case LDPT_GNU_LD_VERSION:
            TVU(val) = major * 100 + minor;
            break;
          case LDPT_LINKER_OUTPUT:
            TVU(val) = link_info.relocatable ? LDPO_REL
                        : (link_info.shared ? LDPO_DYN : LDPO_EXEC);
            break;
          case LDPT_OUTPUT_NAME:
            TVU(string) = output_filename;
            break;
          case LDPT_REGISTER_CLAIM_FILE_HOOK:
            TVU(register_claim_file) = register_claim_file;
            break;
          case LDPT_REGISTER_ALL_SYMBOLS_READ_HOOK:
            TVU(register_all_symbols_read) = register_all_symbols_read;
            break;
          case LDPT_REGISTER_CLEANUP_HOOK:
            TVU(register_cleanup) = register_cleanup;
            break;
          case LDPT_ADD_SYMBOLS:
            TVU(add_symbols) = add_symbols;
            break;
          case LDPT_GET_INPUT_FILE:
            TVU(get_input_file) = get_input_file;
            break;
          case LDPT_RELEASE_INPUT_FILE:
            TVU(release_input_file) = release_input_file;
            break;
          case LDPT_GET_SYMBOLS:
            TVU(get_symbols) = get_symbols;
            break;
          case LDPT_ADD_INPUT_FILE:
            TVU(add_input_file) = add_input_file;
            break;
          case LDPT_ADD_INPUT_LIBRARY:
            TVU(add_input_library) = add_input_library;
            break;
          case LDPT_SET_EXTRA_LIBRARY_PATH:
            TVU(set_extra_library_path) = set_extra_library_path;
            break;
          default:
            /* Added a new entry to the array without adding
               a new case to set up its value is a bug.  */
            FAIL ();
        }
#undef TVU
    }
  return tv_header_size;
}

/* Append the per-plugin args list and trailing LDPT_NULL to tv.  */
static void
set_tv_plugin_args (plugin_t *plugin, struct ld_plugin_tv *tv)
{
  plugin_arg_t *arg = plugin->args;
  while (arg)
    {
      tv->tv_tag = LDPT_OPTION;
      tv->tv_u.tv_string = arg->arg;
      arg = arg->next;
      tv++;
    }
  tv->tv_tag = LDPT_NULL;
  tv->tv_u.tv_val = 0;
}

/* Load up and initialise all plugins after argument parsing.  */
int plugin_load_plugins (void)
{
  struct ld_plugin_tv *my_tv;
  unsigned int max_args = 0;
  plugin_t *curplug = plugins_list;

  /* If there are no plugins, we need do nothing this run.  */
  if (!curplug)
    return 0;

  /* First pass over plugins to find max # args needed so that we
     can size and allocate the tv array.  */
  while (curplug)
    {
      if (curplug->n_args > max_args)
        max_args = curplug->n_args;
      curplug = curplug->next;
    }

  /* Allocate tv array and initialise constant part.  */
  my_tv = xmalloc ((max_args + 1 + tv_header_size) * sizeof *my_tv);
  set_tv_header (my_tv);

  /* Pass over plugins again, activating them.  */
  curplug = plugins_list;
  while (curplug)
    {
      enum ld_plugin_status rv;
      ld_plugin_onload onloadfn = dlsym (curplug->dlhandle, "onload");
      if (!onloadfn)
        onloadfn = dlsym (curplug->dlhandle, "_onload");
      if (!onloadfn)
        return set_plugin_error (curplug->name);
      set_tv_plugin_args (curplug, &my_tv[tv_header_size]);
      called_plugin = curplug;
      rv = (*onloadfn) (my_tv);
      called_plugin = NULL;
      if (rv != LDPS_OK)
        return set_plugin_error (curplug->name);
      curplug = curplug->next;
    }

  /* Since plugin(s) inited ok, assume they're going to want symbol
     resolutions, which needs us to track which symbols are referenced
     by non-IR files using the linker's notice callback.  */
  link_info.notice_all = TRUE;

  return 0;
}

/* Call 'claim file' hook for all plugins.  */
int
plugin_call_claim_file (const struct ld_plugin_input_file *file, int *claimed)
{
  plugin_t *curplug = plugins_list;
  *claimed = FALSE;
  if (no_more_claiming)
    return 0;
  while (curplug && !*claimed)
    {
      if (curplug->claim_file_handler)
        {
          enum ld_plugin_status rv;
          called_plugin = curplug;
          rv = (*curplug->claim_file_handler) (file, claimed);
          called_plugin = NULL;
          if (rv != LDPS_OK)
            set_plugin_error (curplug->name);
        }
      curplug = curplug->next;
    }
  return plugin_error_p () ? -1 : 0;
}

/* Call 'all symbols read' hook for all plugins.  */
int
plugin_call_all_symbols_read (void)
{
  plugin_t *curplug = plugins_list;

  /* Disable any further file-claiming.  */
  no_more_claiming = TRUE;

  /* If --allow-multiple-definition is in effect, we need to disable it,
     as the plugin infrastructure relies on the multiple_definition
     callback to swap out the dummy IR-only BFDs for new real ones
     when it starts opening the files added during this callback.  */
  plugin_cached_allow_multiple_defs = link_info.allow_multiple_definition;
  link_info.allow_multiple_definition = FALSE;

  while (curplug)
    {
      if (curplug->all_symbols_read_handler)
        {
          enum ld_plugin_status rv;
          called_plugin = curplug;
          rv = (*curplug->all_symbols_read_handler) ();
          called_plugin = NULL;
          if (rv != LDPS_OK)
            set_plugin_error (curplug->name);
        }
      curplug = curplug->next;
    }
  return plugin_error_p () ? -1 : 0;
}

/* Call 'cleanup' hook for all plugins.  */
int
plugin_call_cleanup (void)
{
  plugin_t *curplug = plugins_list;
  while (curplug)
    {
      if (curplug->cleanup_handler && !curplug->cleanup_done)
        {
          enum ld_plugin_status rv;
          curplug->cleanup_done = TRUE;
          called_plugin = curplug;
          rv = (*curplug->cleanup_handler) ();
          called_plugin = NULL;
          if (rv != LDPS_OK)
            set_plugin_error (curplug->name);
          dlclose (curplug->dlhandle);
        }
      curplug = curplug->next;
    }
  return plugin_error_p () ? -1 : 0;
}

/* Lazily init the non_ironly hash table.  */
static void
init_non_ironly_hash (void)
{
  if (non_ironly_hash == NULL)
    {
      non_ironly_hash =
          (struct bfd_hash_table *) xmalloc (sizeof (struct bfd_hash_table));
      if (!bfd_hash_table_init_n (non_ironly_hash,
                                  bfd_hash_newfunc,
                                  sizeof (struct bfd_hash_entry),
                                  61))
        einfo (_("%P%F: bfd_hash_table_init failed: %E\n"));
    }
}

/* To determine which symbols should be resolved LDPR_PREVAILING_DEF
   and which LDPR_PREVAILING_DEF_IRONLY, we notice all the symbols as
   the linker adds them to the linker hash table.  If we see a symbol
   being referenced from a non-IR file, we add it to the non_ironly hash
   table.  If we can't find it there at get_symbols time, we know that
   it was referenced only by IR files.  We have to notice_all symbols,
   because we won't necessarily know until later which ones will be
   contributed by IR files.  */
bfd_boolean
plugin_notice (struct bfd_link_info *info ATTRIBUTE_UNUSED,
                const char *name, bfd *abfd,
                asection *section, bfd_vma value ATTRIBUTE_UNUSED)
{
  bfd_boolean is_ref = bfd_is_und_section (section);
  bfd_boolean is_dummy = is_ir_dummy_bfd (abfd);
  init_non_ironly_hash ();
  /* We only care about refs, not defs, indicated by section pointing
     to the undefined section (according to the bfd linker notice callback
     interface definition).  */
  if (is_ref && !is_dummy)
    {
      /* This is a ref from a non-IR file, so note the ref'd symbol
         in the non-IR-only hash.  */
      if (!bfd_hash_lookup (non_ironly_hash, name, TRUE, TRUE))
        einfo (_("%P%X: %s: hash table failure adding symbol %s"),
                abfd->filename, name);
    }
  else if (!is_ref && is_dummy)
    {
      /* No further processing since this is a def from an IR dummy BFD.  */
      return FALSE;
    }

  /* Continue with cref/nocrossref/trace-sym processing.  */
  return TRUE;
}

/* When we add new object files to the link at all symbols read time,
   these contain the real code and symbols generated from the IR files,
   and so duplicate all the definitions already supplied by the dummy
   IR-only BFDs that we created at claim files time.  We use the linker's
   multiple-definitions callback hook to fix up the clash, discarding
   the symbol from the IR-only BFD in favour of the symbol from the
   real BFD.  We return true if this was not-really-a-clash because
   we've fixed it up, or anyway if --allow-multiple-definition was in
   effect (before we disabled it to ensure we got called back).  */
bfd_boolean
plugin_multiple_definition (struct bfd_link_info *info, const char *name,
                bfd *obfd, asection *osec ATTRIBUTE_UNUSED,
                bfd_vma oval ATTRIBUTE_UNUSED,
                bfd *nbfd, asection *nsec, bfd_vma nval)
{
  if (is_ir_dummy_bfd (obfd))
    {
      struct bfd_link_hash_entry *blhe = bfd_link_hash_lookup (info->hash,
                                        name, FALSE, FALSE, FALSE);
      if (!blhe)
        einfo (_("%P%X: %s: can't find IR symbol '%s'"), nbfd->filename,
                name);
      else if (blhe->type != bfd_link_hash_defined)
        einfo (_("%P%x: %s: bad IR symbol type %d"), name, blhe->type);
      /* Replace it with new details.  */
      blhe->u.def.section = nsec;
      blhe->u.def.value = nval;
      return TRUE;
    }
  return plugin_cached_allow_multiple_defs;
}