path: root/gdb/linux-fork.c

/* GNU/Linux native-dependent code for debugging multiple forks.

   Copyright (C) 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc.

   This file is part of GDB.

   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, see <http://www.gnu.org/licenses/>.  */

#include "defs.h"
#include "arch-utils.h"
#include "inferior.h"
#include "regcache.h"
#include "gdbcmd.h"
#include "infcall.h"
#include "objfiles.h"
#include "gdb_assert.h"
#include "gdb_string.h"
#include "linux-fork.h"
#include "linux-nat.h"
#include "checkpoint.h"

#include <sys/ptrace.h>
#include "gdb_wait.h"
#include <sys/param.h>
#include "gdb_dirent.h"
#include <ctype.h>

/* Prevent warning from -Wmissing-prototypes.  */
extern void _initialize_linux_fork (void);

int detach_fork = 1;		/* Default behavior is to detach
				   newly forked processes (legacy).  */

/* Fork list data structure:  */
struct fork_info
{
  struct fork_info *next;
  ptid_t ptid;
  int num;			/* Convenient handle (GDB fork id) */
  struct regcache *savedregs;	/* Convenient for info fork, saves
				   having to actually switch contexts.  */
  int clobber_regs;		/* True if we should restore saved regs.  */
  off_t *filepos;		/* Set of open file descriptors' offsets.  */
  int maxfd;
};

/* Fork list methods now use external checkpoint list.  */

int
forks_exist_p (void)
{
  return (checkpoint_first () != NULL);
}

static void
free_fork (struct fork_info *fp)
{
  /* Notes on step-resume breakpoints: since this is a concern for
     threads, let's convince ourselves that it's not a concern for
     forks.  There are two ways for a fork_info to be created.  First,
     by the checkpoint command, in which case we're at a gdb prompt
     and there can't be any step-resume breakpoint.  Second, by a fork
     in the user program, in which case we *may* have stepped into the
     fork call, but regardless of whether we follow the parent or the
     child, we will return to the same place and the step-resume
     breakpoint, if any, will take care of itself as usual.  And
     unlike threads, we do not save a private copy of the step-resume
     breakpoint -- so we're OK.  */

  if (fp)
    {
      if (fp->savedregs)
	regcache_xfree (fp->savedregs);
      if (fp->filepos)
	xfree (fp->filepos);
      xfree (fp);
    }
}

static void
delete_fork (ptid_t ptid)
{
  struct fork_info *fp;
  struct checkpoint_info *cp;

  for (cp = checkpoint_first (); cp != NULL; cp = checkpoint_next ())
    {
      fp = cp->client_data;
      if (fp && ptid_equal (fp->ptid, ptid))
	break;
    }

  if (!fp)
    return;

  free_fork (fp);
  checkpoint_unlink (cp);

  /* Special case: if there is now only one process in the list,
     and if it is (hopefully!) the current inferior_ptid, then
     remove it, leaving the list empty -- we're now down to the
     default case of debugging a single process.  */
  if (checkpoint_first () != NULL  && checkpoint_next () == NULL)
    {
      cp = checkpoint_first ();
      fp = cp->client_data;
      if (ptid_equal (fp->ptid, inferior_ptid))
	{
	  /* Last fork -- delete from list and handle as solo process
	     (should be a safe recursion).  */
	  delete_fork (inferior_ptid);
	}
    }
}

/* Find a fork_info by matching PTID.  */
static struct fork_info *
find_fork_ptid (ptid_t ptid)
{
  struct fork_info *fp;
  struct checkpoint_info *cp;

  for (cp = checkpoint_first (); cp != NULL; cp = checkpoint_next ())
    {
      fp = cp->client_data;
      if (fp && ptid_equal (fp->ptid, ptid))
	return fp;
    }
  return NULL;
}

/* Find a fork_info by matching ID.  */
static struct fork_info *
find_fork_id (int num)
{
  struct checkpoint_info *cp;

  for (cp = checkpoint_first (); cp != NULL; cp = checkpoint_next ())
    {
      if (cp->checkpoint_id == num)
	return (struct fork_info *) cp->client_data;
    }
  return NULL;
}

/* Find a fork_info by matching pid.  */
extern struct fork_info *
find_fork_pid (pid_t pid)
{
  struct fork_info *fp;
  struct checkpoint_info *cp;

  for (cp = checkpoint_first (); cp != NULL; cp = checkpoint_next ())
    {
      fp = cp->client_data;
      if (fp && pid == ptid_get_pid (fp->ptid))
	return fp;
    }
  return NULL;
}

/* Add a fork to the external checkpoint list.  */

struct fork_info *
add_fork (pid_t pid)
{
  struct checkpoint_info *cp_first = checkpoint_first ();
  struct fork_info *fp;

  if (pid != PIDGET (inferior_ptid) && !find_fork_ptid (inferior_ptid))
    {
      /* Special case -- if inferior_ptid is not in the list, then
	 add inferior_ptid first, as a special zeroeth fork id.  */
      checkpoint_insert (NULL);
      add_fork (PIDGET (inferior_ptid));	/* safe recursion */
    }

  fp = XZALLOC (struct fork_info);
  fp->ptid = ptid_build (pid, pid, 0);
  if (cp_first && cp_first->client_data == NULL)
    cp_first->client_data = fp;
  else
    checkpoint_insert (fp);

#if 0
  fp = find_fork_pid (pid);
  if (fp == NULL)
    {
      fp = XZALLOC (struct fork_info);
      fp->ptid = ptid_build (pid, pid, 0);
      checkpoint_insert (fp);
    }
#endif

  return fp;
}

static ptid_t
fork_id_to_ptid (int num)
{
  struct fork_info *fork = find_fork_id (num);
  if (fork)
    return fork->ptid;
  else
    return pid_to_ptid (-1);
}

/* Fork list <-> gdb interface.  */

/* Utility function for fork_load/fork_save.
   Calls lseek in the (current) inferior process.  */

static off_t
call_lseek (int fd, off_t offset, int whence)
{
  char exp[80];

  snprintf (&exp[0], sizeof (exp), "lseek (%d, %ld, %d)",
	    fd, (long) offset, whence);
  return (off_t) parse_and_eval_long (&exp[0]);
}

/* Load infrun state for the fork PTID.  */

static void
fork_load_infrun_state (struct fork_info *fp)
{
  extern void nullify_last_target_wait_ptid ();
  int i;

  linux_nat_switch_fork (fp->ptid);

  if (fp->savedregs && fp->clobber_regs)
    regcache_cpy (get_current_regcache (), fp->savedregs);

  registers_changed ();
  reinit_frame_cache ();

  stop_pc = regcache_read_pc (get_current_regcache ());
  nullify_last_target_wait_ptid ();

  /* Now restore the file positions of open file descriptors.  */
  if (fp->filepos)
    {
      for (i = 0; i <= fp->maxfd; i++)
	if (fp->filepos[i] != (off_t) -1)
	  call_lseek (i, fp->filepos[i], SEEK_SET);
      /* NOTE: I can get away with using SEEK_SET and SEEK_CUR because
	 this is native-only.  If it ever has to be cross, we'll have
	 to rethink this.  */
    }
}

/* Save infrun state for the fork PTID.
   Exported for use by linux child_follow_fork.  */

static void
fork_save_infrun_state (struct fork_info *fp, int clobber_regs)
{
  char path[MAXPATHLEN];
  struct dirent *de;
  DIR *d;

  if (fp->savedregs)
    regcache_xfree (fp->savedregs);

  fp->savedregs = regcache_dup (get_current_regcache ());
  fp->clobber_regs = clobber_regs;

  if (clobber_regs)
    {
      /* Now save the 'state' (file position) of all open file descriptors.
	 Unfortunately fork does not take care of that for us...  */
      snprintf (path, MAXPATHLEN, "/proc/%ld/fd", (long) PIDGET (fp->ptid));
      if ((d = opendir (path)) != NULL)
	{
	  long tmp;

	  fp->maxfd = 0;
	  while ((de = readdir (d)) != NULL)
	    {
	      /* Count open file descriptors (actually find highest
		 numbered).  */
	      tmp = strtol (&de->d_name[0], NULL, 10);
	      if (fp->maxfd < tmp)
		fp->maxfd = tmp;
	    }
	  /* Allocate array of file positions.  */
	  fp->filepos = xrealloc (fp->filepos,
				  (fp->maxfd + 1) * sizeof (*fp->filepos));

	  /* Initialize to -1 (invalid).  */
	  for (tmp = 0; tmp <= fp->maxfd; tmp++)
	    fp->filepos[tmp] = -1;

	  /* Now find actual file positions.  */
	  rewinddir (d);
	  while ((de = readdir (d)) != NULL)
	    if (isdigit (de->d_name[0]))
	      {
		tmp = strtol (&de->d_name[0], NULL, 10);
		fp->filepos[tmp] = call_lseek (tmp, 0, SEEK_CUR);
	      }
	  closedir (d);
	}
    }
}

/* Kill 'em all, let God sort 'em out...  */

void
linux_fork_killall (void)
{
  /* Walk list and kill every pid.  No need to treat the
     current inferior_ptid as special (we do not return a
     status for it) -- however any process may be a child
     or a parent, so may get a SIGCHLD from a previously
     killed child.  Wait them all out.  */
  struct fork_info *fp;
  struct checkpoint_info *cp;
  pid_t pid, ret;
  int status;

  for (cp = checkpoint_first (); cp != NULL; cp = checkpoint_next ())
    {
      fp = cp->client_data;
      if (!fp)
	continue;

      pid = PIDGET (fp->ptid);
      do {
	/* Use SIGKILL instead of PTRACE_KILL because the former works
	   even if the thread is running, while the later doesn't.  */
	if (info_verbose)
	  printf_filtered (_("Killing checkpoint/fork %d.\n"), pid);
	kill (pid, SIGKILL);
	ret = waitpid (pid, &status, 0);
	/* We might get a SIGCHLD instead of an exit status.  This is
	 aggravated by the first kill above - a child has just
	 died.  MVS comment cut-and-pasted from linux-nat.  */
      } while (ret == pid && WIFSTOPPED (status));
      free_fork (fp);
      checkpoint_unlink (cp);
    }
}

/* The current inferior_ptid has exited, but there are other viable
   forks to debug.  Delete the exiting one and context-switch to the
   first available.  */

void
linux_fork_mourn_inferior (void)
{
  /* Wait just one more time to collect the inferior's exit status.
     Do not check whether this succeeds though, since we may be
     dealing with a process that we attached to.  Such a process will
     only report its exit status to its original parent.  */
  int status;

  waitpid (ptid_get_pid (inferior_ptid), &status, 0);

  /* OK, presumably inferior_ptid is the one who has exited.  
     We need to delete that one from the checkpoint list, and 
     switch to the next available fork.  */
  delete_fork (inferior_ptid);

  /* There should still be a fork - if there's only one left,
     delete_fork won't remove it, because we haven't updated
     inferior_ptid yet.  */
  gdb_assert (checkpoint_first ());

  fork_load_infrun_state (checkpoint_first ()->client_data);
  printf_filtered (_("[Switching to %s]\n"),
		   target_pid_to_str (inferior_ptid));

  /* If there's only one fork, switch back to non-fork mode.  */
  if (checkpoint_next () == NULL)
    delete_fork (inferior_ptid);
}

/* The current inferior_ptid is being detached, but there are other
   viable forks to debug.  Detach and delete it and context-switch to
   the first available.  */

void
linux_fork_detach (char *args, int from_tty)
{
  /* OK, inferior_ptid is the one we are detaching from.  We need
     to delete it from the checkpoint list, and switch to the next
     available fork.  */

  if (ptrace (PTRACE_DETACH, PIDGET (inferior_ptid), 0, 0))
    error (_("Unable to detach %s"), target_pid_to_str (inferior_ptid));

  delete_fork (inferior_ptid);

  /* There should still be a fork - if there's only one left,
     delete_fork won't remove it, because we haven't updated
     inferior_ptid yet.  */
  gdb_assert (checkpoint_first ());

  fork_load_infrun_state (checkpoint_first ()->client_data);

  if (from_tty)
    printf_filtered (_("[Switching to %s]\n"),
		     target_pid_to_str (inferior_ptid));

  /* If there's only one fork, switch back to non-fork mode.  */
  if (checkpoint_next () == NULL)
    delete_fork (inferior_ptid);
}

/* Fork checkpoint list <-> target interface.  */

/* target_unset_checkpoint == linux_unset_checkpoint.  */

static void
linux_unset_checkpoint (struct checkpoint_info *cp, int from_tty)
{
  ptid_t ptid = ((struct fork_info *) cp->client_data)->ptid;

  if (ptid_equal (ptid, inferior_ptid))
    error (_("\
Please switch to another checkpoint before deleting the current one"));

  if (ptrace (PTRACE_KILL, PIDGET (ptid), 0, 0))
    error (_("Unable to kill pid %s"), target_pid_to_str (ptid));

  if (from_tty)
    printf_filtered (_("Killed %s\n"), target_pid_to_str (ptid));

  delete_fork (ptid);
}

static void
detach_checkpoint_command (char *args, int from_tty)
{
  ptid_t ptid;

  if (!args || !*args)
    error (_("Requires argument (checkpoint id to detach)"));

  ptid = fork_id_to_ptid (parse_and_eval_long (args));
  if (ptid_equal (ptid, minus_one_ptid))
    error (_("No such checkpoint id, %s"), args);

  if (ptid_equal (ptid, inferior_ptid))
    error (_("\
Please switch to another checkpoint before detaching the current one"));

  if (ptrace (PTRACE_DETACH, PIDGET (ptid), 0, 0))
    error (_("Unable to detach %s"), target_pid_to_str (ptid));

  if (from_tty)
    printf_filtered (_("Detached %s\n"), target_pid_to_str (ptid));

  delete_fork (ptid);
}

/* target_info_checkpoints == linux_show_checkpoints_info.  */

static void
linux_show_checkpoints_info (struct checkpoint_info *cp, int from_tty)
{
  struct gdbarch *gdbarch = get_current_arch ();
  struct frame_info *cur_frame;
  struct symtab_and_line sal;
  struct symtab *cur_symtab;
  struct fork_info *fp = cp->client_data;
  int cur_line;
  ULONGEST pc;

  if (ptid_equal (fp->ptid, inferior_ptid))
    {
      printf_filtered ("* ");
      pc = regcache_read_pc (get_current_regcache ());
    }
  else
    {
      printf_filtered ("  ");
      pc = regcache_read_pc (fp->savedregs);
    }
  printf_filtered ("%d %s", cp->checkpoint_id, target_pid_to_str (fp->ptid));
  if (cp->checkpoint_id == 0)
    printf_filtered (_(" (main process)"));
  printf_filtered (_(" at "));
  fputs_filtered (paddress (gdbarch, pc), gdb_stdout);

  sal = find_pc_line (pc, 0);
  if (sal.symtab)
    {
      char *tmp = strrchr (sal.symtab->filename, '/');

      if (tmp)
	printf_filtered (_(", file %s"), tmp + 1);
      else
	printf_filtered (_(", file %s"), sal.symtab->filename);
    }
  if (sal.line)
    printf_filtered (_(", line %d"), sal.line);
  if (!sal.symtab && !sal.line)
    {
      struct minimal_symbol *msym;

      msym = lookup_minimal_symbol_by_pc (pc);
      if (msym)
	printf_filtered (", <%s>", SYMBOL_LINKAGE_NAME (msym));
    }

  putchar_filtered ('\n');
}

/* The PID of the process we're checkpointing.  */
static int checkpointing_pid = 0;

int
linux_fork_checkpointing_p (int pid)
{
  return (checkpointing_pid == pid);
}

/* target_set_checkpoint == linux_set_checkpoint.  */

static void *
linux_set_checkpoint (struct checkpoint_info *cp, int from_tty)
{
  struct objfile *fork_objf;
  struct gdbarch *gdbarch;
  struct target_waitstatus last_target_waitstatus;
  ptid_t last_target_ptid;
  struct value *fork_fn = NULL, *ret;
  struct fork_info *fp;
  pid_t retpid;
  struct cleanup *old_chain;
  long i;

  /* Make the inferior fork, record its (and gdb's) state.  */

  if (lookup_minimal_symbol ("fork", NULL, NULL) != NULL)
    fork_fn = find_function_in_inferior ("fork", &fork_objf);
  if (!fork_fn)
    if (lookup_minimal_symbol ("_fork", NULL, NULL) != NULL)
      fork_fn = find_function_in_inferior ("fork", &fork_objf);
  if (!fork_fn)
    error (_("checkpoint: can't find fork function in inferior."));

  gdbarch = get_objfile_arch (fork_objf);
  ret = value_from_longest (builtin_type (gdbarch)->builtin_int, 0);

  /* Tell linux-nat.c that we're checkpointing this inferior.  */
  old_chain = make_cleanup_restore_integer (&checkpointing_pid);
  checkpointing_pid = PIDGET (inferior_ptid);

  ret = call_function_by_hand (fork_fn, 0, &ret);
  do_cleanups (old_chain);
  if (!ret)	/* Probably can't happen.  */
    error (_("checkpoint: call_function_by_hand returned null."));

  retpid = value_as_long (ret);
  get_last_target_status (&last_target_ptid, &last_target_waitstatus);
  if (from_tty)
    {
      int parent_pid;

      printf_filtered (_(": fork returned pid %ld.\n"),
		       (long) retpid);
      if (info_verbose)
	{
	  parent_pid = ptid_get_lwp (last_target_ptid);
	  if (parent_pid == 0)
	    parent_pid = ptid_get_pid (last_target_ptid);
	  printf_filtered (_("   gdb says parent = %ld.\n"),
			   (long) parent_pid);
	}
    }

  fp = find_fork_pid (retpid);
  if (!fp)
    error (_("Failed to find new fork"));
  fork_save_infrun_state (fp, 1);

  return fp;
}

/* target_restore_checkpoint == linux_restore_checkpoint.  */

static void
linux_restore_checkpoint (struct checkpoint_info *cp, int from_tty)
{
  linux_fork_context ((struct fork_info *) cp->client_data, from_tty);
}

void
_initialize_linux_fork (void)
{
  struct target_ops *t;

  /* Set/show detach-on-fork: user-settable mode.  */

  add_setshow_boolean_cmd ("detach-on-fork", class_obscure, &detach_fork, _("\
Set whether gdb will detach the child of a fork."), _("\
Show whether gdb will detach the child of a fork."), _("\
Tells gdb whether to detach the child of a fork."),
			   NULL, NULL, &setlist, &showlist);

  /* Detach checkpoint command: release the process to run independently,
     and remove it from the fork list.  */

  add_cmd ("checkpoint", class_obscure, detach_checkpoint_command, _("\
Detach from a checkpoint (experimental)."),
	   &detachlist);

  /* Get the linux target vector.  */
  t = linux_target ();
  /* Add checkpoint target methods.  */
  t->to_set_checkpoint = linux_set_checkpoint;
  t->to_unset_checkpoint = linux_unset_checkpoint;
  t->to_restore_checkpoint = linux_restore_checkpoint;
  t->to_info_checkpoints = linux_show_checkpoints_info;

  /* Activate the checkpoint module.  */
  checkpoint_init ();

  /* XXX mvs call linux_target and add checkpoint methods.  
         to_set_checkpoint
         to_unset_checkpoint
	 to_info_checkpoints (maybe this could be common?  Maybe not?
	 to_detach_checkpoint (esoteric?)
	 to_restore_checkpoint.

     Make a new module called checkpoint.c, include it always, but
     don't make it auto-initialize like most modules.  Instead, 
     give it a global entry point checkpoint_init, which has to be
     called explicitly by targets that want to activate the 
     checkpoint commands.
  */
}