third_party_elfutils/libdwfl_stacktrace/dwflst_process_tracker.c

/* Track multiple Dwfl structs for multiple processes.
   Copyright (C) 2025, Red Hat, Inc.
   This file is part of elfutils.

   This file is free software; you can redistribute it and/or modify
   it under the terms of either

     * the GNU Lesser General Public License as published by the Free
       Software Foundation; either version 3 of the License, or (at
       your option) any later version

   or

     * 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

   or both in parallel, as here.

   elfutils 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 copies of the GNU General Public License and
   the GNU Lesser General Public License along with this program.  If
   not, see <http://www.gnu.org/licenses/>.  */

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

#include "libdwfl_stacktraceP.h"

#define HTAB_DEFAULT_SIZE 1021

Dwflst_Process_Tracker *dwflst_tracker_begin (const Dwfl_Callbacks *callbacks)
{
  Dwflst_Process_Tracker *tracker = calloc (1, sizeof *tracker);
  if (tracker == NULL)
    {
      __libdwfl_seterrno (DWFL_E_NOMEM);
      return tracker;
    }

  dwflst_tracker_elftab_init (&tracker->elftab, HTAB_DEFAULT_SIZE);
  rwlock_init (tracker->elftab_lock);
  dwflst_tracker_dwfltab_init (&tracker->dwfltab, HTAB_DEFAULT_SIZE);
  rwlock_init (tracker->dwfltab_lock);

  tracker->callbacks = callbacks;
  return tracker;
}

Dwfl *dwflst_tracker_dwfl_begin (Dwflst_Process_Tracker *tracker)
{
  Dwfl *dwfl = INTUSE(dwfl_begin) (tracker->callbacks);
  if (dwfl == NULL)
    return dwfl;

  /* TODO: Could also share dwfl->debuginfod, but thread-safely? */
  dwfl->tracker = tracker;

  /* XXX: dwfl added to dwfltab when dwfl->process set in dwfl_attach_state. */
  /* XXX: dwfl removed from dwfltab in dwfl_end() */

  return dwfl;
}

Dwfl *dwflst_tracker_find_pid (Dwflst_Process_Tracker *tracker,
			       pid_t pid,
			       Dwfl *(*callback) (Dwflst_Process_Tracker *,
						  pid_t, void *),
			       void *arg)
{
  Dwfl *dwfl = NULL;

  rwlock_rdlock (tracker->dwfltab_lock);
  dwflst_tracker_dwfl_info *ent
    = dwflst_tracker_dwfltab_find(&tracker->dwfltab, pid);
  rwlock_unlock (tracker->dwfltab_lock);

  if (ent != NULL && !ent->invalid)
    dwfl = ent->dwfl;
  if (dwfl == NULL && callback != NULL)
    dwfl = callback(tracker, pid, arg);
  if (dwfl != NULL)
    {
      assert (dwfl->tracker == tracker);
      /* XXX: dwfl added to dwfltab when dwfl->process set in dwfl_attach_state.
         Prior to that, the pid is not confirmed. */
    }

  return dwfl;
}

void
internal_function
__libdwfl_stacktrace_add_dwfl_to_tracker (Dwfl *dwfl) {
  Dwflst_Process_Tracker *tracker = dwfl->tracker;
  assert (tracker != NULL);

  /* First try to find an existing entry to replace: */
  dwflst_tracker_dwfl_info *ent = NULL;
  unsigned long int hval = dwfl->process->pid;

  rwlock_wrlock (tracker->dwfltab_lock);
  ent = dwflst_tracker_dwfltab_find(&tracker->dwfltab, hval);
  if (ent != NULL)
    {
      /* TODO: This is a bare-minimum solution. Ideally
         we would clean up the existing ent->dwfl, but
         this needs to be coordinated with any users of
         the dwfl library that might still be holding it. */
      ent->dwfl = dwfl;
      ent->invalid = false;
      rwlock_unlock (tracker->dwfltab_lock);
      return;
    }

  /* Only otherwise try to insert an entry: */
  ent = calloc (1, sizeof(dwflst_tracker_dwfl_info));
  if (ent == NULL)
    {
      rwlock_unlock (tracker->dwfltab_lock);
      __libdwfl_seterrno (DWFL_E_NOMEM);
      return;
    }
  ent->dwfl = dwfl;
  ent->invalid = false;
  if (dwflst_tracker_dwfltab_insert(&tracker->dwfltab, hval, ent) != 0)
    {
      free(ent);
      rwlock_unlock (tracker->dwfltab_lock);
      assert(false); /* Should not occur due to the wrlock on dwfltab. */
    }
  rwlock_unlock (tracker->dwfltab_lock);
}

void
internal_function
__libdwfl_stacktrace_remove_dwfl_from_tracker (Dwfl *dwfl) {
  if (dwfl->tracker == NULL)
    return;
  Dwflst_Process_Tracker *tracker = dwfl->tracker;
  dwflst_tracker_dwfl_info *ent = NULL;
  if (dwfl->process == NULL)
    return;
  unsigned long int hval = dwfl->process->pid;

  rwlock_wrlock (tracker->dwfltab_lock);
  ent = dwflst_tracker_dwfltab_find(&tracker->dwfltab, hval);
  if (ent != NULL && ent->dwfl == dwfl)
    {
      ent->dwfl = NULL;
      ent->invalid = true;
    }
  rwlock_unlock (tracker->dwfltab_lock);
}

void dwflst_tracker_end (Dwflst_Process_Tracker *tracker)
{
  if (tracker == NULL)
    return;

  size_t idx;

  /* HACK to allow iteration of dynamicsizehash_concurrent.  */
  /* XXX Based on lib/dynamicsizehash_concurrent.c free().  */
  rwlock_fini (tracker->elftab_lock);
  pthread_rwlock_destroy(&tracker->elftab.resize_rwl);
  for (idx = 1; idx <= tracker->elftab.size; idx++)
    {
      dwflst_tracker_elftab_ent *ent = &tracker->elftab.table[idx];
      if (ent->hashval == 0)
	continue;
      dwflst_tracker_elf_info *t =
	(dwflst_tracker_elf_info *) atomic_load_explicit (&ent->val_ptr,
							  memory_order_relaxed);
      free(t->module_name);
      if (t->fd >= 0)
	close(t->fd);
      if (t->elf != NULL)
	elf_end(t->elf);
      free(t); /* TODO: Check necessity. */
    }
  free (tracker->elftab.table);

  /* XXX Based on lib/dynamicsizehash_concurrent.c free().  */
  rwlock_fini (tracker->dwfltab_lock);
  pthread_rwlock_destroy(&tracker->dwfltab.resize_rwl);
  for (idx = 1; idx <= tracker->dwfltab.size; idx++)
    {
      dwflst_tracker_dwfltab_ent *ent = &tracker->dwfltab.table[idx];
      if (ent->hashval == 0)
	continue;
      dwflst_tracker_dwfl_info *t =
	(dwflst_tracker_dwfl_info *) atomic_load_explicit (&ent->val_ptr,
							   memory_order_relaxed);
      if (t->dwfl != NULL)
	INTUSE(dwfl_end) (t->dwfl);
      free(t);
    }
  free (tracker->dwfltab.table);

  free (tracker);
}