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binutils-gdb/gdb/linux-fork.c

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/* GNU/Linux native-dependent code for debugging multiple forks.
Copyright (C) 2005-2019 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 "infrun.h"
#include "regcache.h"
#include "gdbcmd.h"
#include "infcall.h"
#include "objfiles.h"
#include "linux-fork.h"
#include "linux-nat.h"
#include "gdbthread.h"
#include "source.h"
#include "nat/gdb_ptrace.h"
#include "gdb_wait.h"
#include <dirent.h>
#include <ctype.h>
struct fork_info *fork_list;
static int highest_fork_num;
/* Fork list data structure: */
struct fork_info
{
struct fork_info *next;
ptid_t ptid;
ptid_t parent_ptid;
int num; /* Convenient handle (GDB fork id). */
readonly_detached_regcache *savedregs; /* Convenient for info fork, saves
having to actually switch contexts. */
CORE_ADDR pc;
int clobber_regs; /* True if we should restore saved regs. */
off_t *filepos; /* Set of open file descriptors' offsets. */
int maxfd;
};
/* Fork list methods: */
int
forks_exist_p (void)
{
return (fork_list != NULL);
}
/* Return the last fork in the list. */
static struct fork_info *
find_last_fork (void)
{
struct fork_info *last;
if (fork_list == NULL)
return NULL;
for (last = fork_list; last->next != NULL; last = last->next)
;
return last;
}
/* Add a fork to the internal fork list. */
struct fork_info *
add_fork (pid_t pid)
{
struct fork_info *fp;
if (fork_list == NULL && pid != inferior_ptid.pid ())
{
/* Special case -- if this is the first fork in the list
(the list is hitherto empty), and if this new fork is
NOT the current inferior_ptid, then add inferior_ptid
first, as a special zeroeth fork id. */
highest_fork_num = -1;
add_fork (inferior_ptid.pid ()); /* safe recursion */
}
fp = XCNEW (struct fork_info);
fp->ptid = ptid_t (pid, pid, 0);
fp->num = ++highest_fork_num;
if (fork_list == NULL)
fork_list = fp;
else
{
struct fork_info *last = find_last_fork ();
last->next = fp;
}
return fp;
}
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)
delete fp->savedregs;
if (fp->filepos)
xfree (fp->filepos);
xfree (fp);
}
}
static void
delete_fork (ptid_t ptid)
{
struct fork_info *fp, *fpprev;
fpprev = NULL;
linux_target->low_forget_process (ptid.pid ());
for (fp = fork_list; fp; fpprev = fp, fp = fp->next)
if (fp->ptid == ptid)
break;
if (!fp)
return;
if (fpprev)
fpprev->next = fp->next;
else
fork_list = fp->next;
free_fork (fp);
/* 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 (fork_list != NULL && fork_list->next == NULL &&
fork_list->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;
for (fp = fork_list; fp; fp = fp->next)
if (fp->ptid == ptid)
return fp;
return NULL;
}
/* Find a fork_info by matching ID. */
static struct fork_info *
find_fork_id (int num)
{
struct fork_info *fp;
for (fp = fork_list; fp; fp = fp->next)
if (fp->num == num)
return fp;
return NULL;
}
/* Find a fork_info by matching pid. */
extern struct fork_info *
find_fork_pid (pid_t pid)
{
struct fork_info *fp;
for (fp = fork_list; fp; fp = fp->next)
if (pid == fp->ptid.pid ())
return fp;
return NULL;
}
static ptid_t
fork_id_to_ptid (int num)
{
struct fork_info *fork = find_fork_id (num);
if (fork)
return fork->ptid;
else
return ptid_t (-1);
}
static void
init_fork_list (void)
{
struct fork_info *fp, *fpnext;
if (!fork_list)
return;
for (fp = fork_list; fp; fp = fpnext)
{
fpnext = fp->next;
free_fork (fp);
}
fork_list = NULL;
}
/* 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), "(long) 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)
get_current_regcache ()->restore (fp->savedregs);
registers_changed ();
reinit_frame_cache ();
inferior_thread ()->suspend.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[PATH_MAX];
struct dirent *de;
DIR *d;
if (fp->savedregs)
delete fp->savedregs;
fp->savedregs = new readonly_detached_regcache (*get_current_regcache ());
fp->pc = regcache_read_pc (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, PATH_MAX, "/proc/%ld/fd",
(long) fp->ptid.pid ());
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 = XRESIZEVEC (off_t, fp->filepos, fp->maxfd + 1);
/* 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;
pid_t pid, ret;
int status;
for (fp = fork_list; fp; fp = fp->next)
{
pid = fp->ptid.pid ();
do {
/* Use SIGKILL instead of PTRACE_KILL because the former works even
if the thread is running, while the later doesn't. */
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));
}
init_fork_list (); /* Clear list, prepare to start fresh. */
}
/* 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)
{
struct fork_info *last;
int status;
/* 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. */
waitpid (inferior_ptid.pid (), &status, 0);
/* OK, presumably inferior_ptid is the one who has exited.
We need to delete that one from the fork_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 (fork_list);
last = find_last_fork ();
fork_load_infrun_state (last);
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 (fork_list->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 (int from_tty)
{
/* OK, inferior_ptid is the one we are detaching from. We need to
delete it from the fork_list, and switch to the next available
fork. */
if (ptrace (PTRACE_DETACH, inferior_ptid.pid (), 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 (fork_list);
fork_load_infrun_state (fork_list);
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 (fork_list->next == NULL)
delete_fork (inferior_ptid);
}
/* Temporarily switch to the infrun state stored on the fork_info
identified by a given ptid_t. When this object goes out of scope,
restore the currently selected infrun state. */
class scoped_switch_fork_info
{
public:
/* Switch to the infrun state held on the fork_info identified by
PPTID. If PPTID is the current inferior then no switch is done. */
explicit scoped_switch_fork_info (ptid_t pptid)
: m_oldfp (nullptr)
{
if (pptid != inferior_ptid)
{
struct fork_info *newfp = nullptr;
/* Switch to pptid. */
m_oldfp = find_fork_ptid (inferior_ptid);
gdb_assert (m_oldfp != nullptr);
newfp = find_fork_ptid (pptid);
gdb_assert (newfp != nullptr);
fork_save_infrun_state (m_oldfp, 1);
remove_breakpoints ();
fork_load_infrun_state (newfp);
insert_breakpoints ();
}
}
/* Restore the previously selected infrun state. If the constructor
didn't need to switch states, then nothing is done here either. */
~scoped_switch_fork_info ()
{
if (m_oldfp != nullptr)
{
/* Switch back to inferior_ptid. */
TRY
{
remove_breakpoints ();
fork_load_infrun_state (m_oldfp);
insert_breakpoints ();
}
CATCH (ex, RETURN_MASK_ALL)
{
warning (_("Couldn't restore checkpoint state in %s: %s"),
target_pid_to_str (m_oldfp->ptid), ex.message);
}
END_CATCH
}
}
DISABLE_COPY_AND_ASSIGN (scoped_switch_fork_info);
private:
/* The fork_info for the previously selected infrun state, or nullptr if
we were already in the desired state, and nothing needs to be
restored. */
struct fork_info *m_oldfp;
};
static int
inferior_call_waitpid (ptid_t pptid, int pid)
{
struct objfile *waitpid_objf;
struct value *waitpid_fn = NULL;
int ret = -1;
scoped_switch_fork_info switch_fork_info (pptid);
/* Get the waitpid_fn. */
if (lookup_minimal_symbol ("waitpid", NULL, NULL).minsym != NULL)
waitpid_fn = find_function_in_inferior ("waitpid", &waitpid_objf);
if (!waitpid_fn
&& lookup_minimal_symbol ("_waitpid", NULL, NULL).minsym != NULL)
waitpid_fn = find_function_in_inferior ("_waitpid", &waitpid_objf);
if (waitpid_fn != nullptr)
{
struct gdbarch *gdbarch = get_current_arch ();
struct value *argv[3], *retv;
/* Get the argv. */
argv[0] = value_from_longest (builtin_type (gdbarch)->builtin_int, pid);
argv[1] = value_from_pointer (builtin_type (gdbarch)->builtin_data_ptr, 0);
argv[2] = value_from_longest (builtin_type (gdbarch)->builtin_int, 0);
retv = call_function_by_hand (waitpid_fn, NULL, argv);
if (value_as_long (retv) >= 0)
ret = 0;
}
return ret;
}
/* Fork list <-> user interface. */
static void
delete_checkpoint_command (const char *args, int from_tty)
{
ptid_t ptid, pptid;
struct fork_info *fi;
if (!args || !*args)
error (_("Requires argument (checkpoint id to delete)"));
ptid = fork_id_to_ptid (parse_and_eval_long (args));
if (ptid == minus_one_ptid)
error (_("No such checkpoint id, %s"), args);
if (ptid == inferior_ptid)
error (_("\
Please switch to another checkpoint before deleting the current one"));
if (ptrace (PTRACE_KILL, ptid.pid (), 0, 0))
error (_("Unable to kill pid %s"), target_pid_to_str (ptid));
fi = find_fork_ptid (ptid);
gdb_assert (fi);
pptid = fi->parent_ptid;
if (from_tty)
printf_filtered (_("Killed %s\n"), target_pid_to_str (ptid));
delete_fork (ptid);
/* If fi->parent_ptid is not a part of lwp but it's a part of checkpoint
list, waitpid the ptid.
If fi->parent_ptid is a part of lwp and it is stopped, waitpid the
ptid. */
thread_info *parent = find_thread_ptid (pptid);
if ((parent == NULL && find_fork_ptid (pptid))
|| (parent != NULL && parent->state == THREAD_STOPPED))
{
if (inferior_call_waitpid (pptid, ptid.pid ()))
warning (_("Unable to wait pid %s"), target_pid_to_str (ptid));
}
}
static void
detach_checkpoint_command (const 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 == minus_one_ptid)
error (_("No such checkpoint id, %s"), args);
if (ptid == inferior_ptid)
error (_("\
Please switch to another checkpoint before detaching the current one"));
if (ptrace (PTRACE_DETACH, ptid.pid (), 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);
}
/* Print information about currently known checkpoints. */
static void
info_checkpoints_command (const char *arg, int from_tty)
{
struct gdbarch *gdbarch = get_current_arch ();
struct symtab_and_line sal;
struct fork_info *fp;
ULONGEST pc;
int requested = -1;
struct fork_info *printed = NULL;
if (arg && *arg)
requested = (int) parse_and_eval_long (arg);
for (fp = fork_list; fp; fp = fp->next)
{
if (requested > 0 && fp->num != requested)
continue;
printed = fp;
if (fp->ptid == inferior_ptid)
printf_filtered ("* ");
else
printf_filtered (" ");
pc = fp->pc;
printf_filtered ("%d %s", fp->num, target_pid_to_str (fp->ptid));
if (fp->num == 0)
printf_filtered (_(" (main process)"));
printf_filtered (_(" at "));
fputs_filtered (paddress (gdbarch, pc), gdb_stdout);
sal = find_pc_line (pc, 0);
if (sal.symtab)
printf_filtered (_(", file %s"),
symtab_to_filename_for_display (sal.symtab));
if (sal.line)
printf_filtered (_(", line %d"), sal.line);
if (!sal.symtab && !sal.line)
{
struct bound_minimal_symbol msym;
msym = lookup_minimal_symbol_by_pc (pc);
if (msym.minsym)
printf_filtered (", <%s>", MSYMBOL_LINKAGE_NAME (msym.minsym));
}
putchar_filtered ('\n');
}
if (printed == NULL)
{
if (requested > 0)
printf_filtered (_("No checkpoint number %d.\n"), requested);
else
printf_filtered (_("No checkpoints.\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);
}
/* Callback for iterate over threads. Used to check whether
the current inferior is multi-threaded. Returns true as soon
as it sees the second thread of the current inferior. */
static int
inf_has_multiple_thread_cb (struct thread_info *tp, void *data)
{
int *count_p = (int *) data;
if (current_inferior ()->pid == tp->ptid.pid ())
(*count_p)++;
/* Stop the iteration if multiple threads have been detected. */
return *count_p > 1;
}
/* Return true if the current inferior is multi-threaded. */
static int
inf_has_multiple_threads (void)
{
int count = 0;
iterate_over_threads (inf_has_multiple_thread_cb, &count);
return (count > 1);
}
static void
checkpoint_command (const char *args, 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;
if (!target_has_execution)
error (_("The program is not being run."));
/* Ensure that the inferior is not multithreaded. */
update_thread_list ();
if (inf_has_multiple_threads ())
error (_("checkpoint: can't checkpoint multiple threads."));
/* Make the inferior fork, record its (and gdb's) state. */
if (lookup_minimal_symbol ("fork", NULL, NULL).minsym != NULL)
fork_fn = find_function_in_inferior ("fork", &fork_objf);
if (!fork_fn)
if (lookup_minimal_symbol ("_fork", NULL, NULL).minsym != 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. */
{
scoped_restore save_pid
= make_scoped_restore (&checkpointing_pid, inferior_ptid.pid ());
ret = call_function_by_hand (fork_fn, NULL, {});
}
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);
fp = find_fork_pid (retpid);
if (from_tty)
{
int parent_pid;
printf_filtered (_("checkpoint %d: fork returned pid %ld.\n"),
fp != NULL ? fp->num : -1, (long) retpid);
if (info_verbose)
{
parent_pid = last_target_ptid.lwp ();
if (parent_pid == 0)
parent_pid = last_target_ptid.pid ();
printf_filtered (_(" gdb says parent = %ld.\n"),
(long) parent_pid);
}
}
if (!fp)
error (_("Failed to find new fork"));
fork_save_infrun_state (fp, 1);
fp->parent_ptid = last_target_ptid;
}
static void
linux_fork_context (struct fork_info *newfp, int from_tty)
{
/* Now we attempt to switch processes. */
struct fork_info *oldfp;
gdb_assert (newfp != NULL);
oldfp = find_fork_ptid (inferior_ptid);
gdb_assert (oldfp != NULL);
fork_save_infrun_state (oldfp, 1);
remove_breakpoints ();
fork_load_infrun_state (newfp);
insert_breakpoints ();
printf_filtered (_("Switching to %s\n"),
target_pid_to_str (inferior_ptid));
print_stack_frame (get_selected_frame (NULL), 1, SRC_AND_LOC, 1);
}
/* Switch inferior process (checkpoint) context, by checkpoint id. */
static void
restart_command (const char *args, int from_tty)
{
struct fork_info *fp;
if (!args || !*args)
error (_("Requires argument (checkpoint id to restart)"));
if ((fp = find_fork_id (parse_and_eval_long (args))) == NULL)
error (_("Not found: checkpoint id %s"), args);
linux_fork_context (fp, from_tty);
}
void
_initialize_linux_fork (void)
{
init_fork_list ();
/* Checkpoint command: create a fork of the inferior process
and set it aside for later debugging. */
add_com ("checkpoint", class_obscure, checkpoint_command, _("\
Fork a duplicate process (experimental)."));
/* Restart command: restore the context of a specified checkpoint
process. */
add_com ("restart", class_obscure, restart_command, _("\
restart N: restore program context from a checkpoint.\n\
Argument N is checkpoint ID, as displayed by 'info checkpoints'."));
/* Delete checkpoint command: kill the process and remove it from
the fork list. */
add_cmd ("checkpoint", class_obscure, delete_checkpoint_command, _("\
Delete a checkpoint (experimental)."),
&deletelist);
/* 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);
/* Info checkpoints command: list all forks/checkpoints
currently under gdb's control. */
add_info ("checkpoints", info_checkpoints_command,
_("IDs of currently known checkpoints."));
}
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