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Linux: on attach, attach to lwps listed under /proc/$pid/task/ 

... instead of relying on libthread_db.

I wrote a test that attaches to a program that constantly spawns
short-lived threads, which exposed several issues.  This is one of
them.

On Linux, we need to attach to all threads of a process (thread group)
individually.  We currently rely on libthread_db to list the threads,
but that is problematic, because libthread_db relies on reading data
structures out of the inferior (which may well be corrupted).  If
threads are being created or exiting just while we try to attach, we
may trip on inconsistencies in the inferior's thread list.  To work
around that, when we see a seemingly corrupt list, we currently retry
a few times:

 static void
 thread_db_find_new_threads_2 (ptid_t ptid, int until_no_new)
 {
 ...
   if (until_no_new)
     {
       /* Require 4 successive iterations which do not find any new threads.
	  The 4 is a heuristic: there is an inherent race here, and I have
	  seen that 2 iterations in a row are not always sufficient to
	  "capture" all threads.  */
 ...

That heuristic may well fail, and when it does, we end up with threads
in the program that aren't under GDB's control.  That's obviously bad
and results in quite mistifying failures, like e.g., the process dying
for seeminly no reason when a thread that wasn't attached trips on a
breakpoint.

There's really no reason to rely on libthread_db for this nowadays
when we have /proc mounted.  In that case, which is the usual case, we
can list the LWPs from /proc/PID/task/.  In fact, GDBserver is already
doing this.  The patch factors out that code that knows to walk the
task/ directory out of GDBserver, and makes GDB use it too.

Like GDBserver, the patch makes GDB attach to LWPs and _not_ wait for
them to stop immediately.  Instead, we just tag the LWP as having an
expected stop.  Because we can only set the ptrace options when the
thread stops, we need a new flag in the lwp structure to keep track of
whether we've already set the ptrace options, just like in GDBserver.
Note that nothing issues any ptrace command to the threads between the
PTRACE_ATTACH and the stop, so this is safe (unlike one scenario
described in gdbserver's linux-low.c).

When we attach to a program that has threads exiting while we attach,
it's easy to race with a thread just exiting as we try to attach to
it, like:

  #1 - get current list of threads
  #2 - attach to each listed thread
  #3 - ooops, attach failed, thread is already gone

As this is pretty normal, we shouldn't be issuing a scary warning in
step #3.

When #3 happens, PTRACE_ATTACH usually fails with ESRCH, but sometimes
we'll see EPERM as well.  That happens when the kernel still has the
thread in its task list, but the thread is marked as dead.
Unfortunately, EPERM is ambiguous and we'll get it also on other
scenarios where the thread isn't dead, and in those cases, it's useful
to get a warning.  To distiguish the cases, when we get an EPERM
failure, we open /proc/PID/status, and check the thread's state -- if
the /proc file no longer exists, or the state is "Z (Zombie)" or "X
(Dead)", we ignore the EPERM error silently; otherwise, we'll warn.
Unfortunately, there seems to be a kernel race here.  Sometimes I get
EPERM, and then the /proc state still indicates "R (Running)"...  If
we wait a bit and retry, we do end up seeing X or Z state, or get an
ESRCH.  I thought of making GDB retry the attach a few times, but even
with a 500ms wait and 4 retries, I still see the warning sometimes.  I
haven't been able to identify the kernel path that causes this yet,
but in any case, it looks like a kernel bug to me.  As this just
results failure to suppress a warning that we've been printing since
about forever anyway, I'm just making the test cope with it, and issue
an XFAIL.

gdb/gdbserver/
2015-01-09  Pedro Alves  <palves@redhat.com>

	* linux-low.c (linux_attach_fail_reason_string): Move to
	nat/linux-ptrace.c, and rename.
	(linux_attach_lwp): Update comment.
	(attach_proc_task_lwp_callback): New function.
	(linux_attach): Adjust to rename and use
	linux_proc_attach_tgid_threads.
	(linux_attach_fail_reason_string): Delete declaration.

gdb/
2015-01-09  Pedro Alves  <palves@redhat.com>

	* linux-nat.c (attach_proc_task_lwp_callback): New function.
	(linux_nat_attach): Use linux_proc_attach_tgid_threads.
	(wait_lwp, linux_nat_filter_event): If not set yet, set the lwp's
	ptrace option flags.
	* linux-nat.h (struct lwp_info) <must_set_ptrace_flags>: New
	field.
	* nat/linux-procfs.c: Include <dirent.h>.
	(linux_proc_get_int): New parameter "warn".  Handle it.
	(linux_proc_get_tgid): Adjust.
	(linux_proc_get_tracerpid): Rename to ...
	(linux_proc_get_tracerpid_nowarn): ... this.
	(linux_proc_pid_get_state): New function, factored out from
	(linux_proc_pid_has_state): ... this.  Add new parameter "warn"
	and handle it.
	(linux_proc_pid_is_gone): New function.
	(linux_proc_pid_is_stopped): Adjust.
	(linux_proc_pid_is_zombie_maybe_warn)
	(linux_proc_pid_is_zombie_nowarn): New functions.
	(linux_proc_pid_is_zombie): Use
	linux_proc_pid_is_zombie_maybe_warn.
	(linux_proc_attach_tgid_threads): New function.
	* nat/linux-procfs.h (linux_proc_get_tgid): Update comment.
	(linux_proc_get_tracerpid): Rename to ...
	(linux_proc_get_tracerpid_nowarn): ... this, and update comment.
	(linux_proc_pid_is_gone): New declaration.
	(linux_proc_pid_is_zombie): Update comment.
	(linux_proc_pid_is_zombie_nowarn): New declaration.
	(linux_proc_attach_lwp_func): New typedef.
	(linux_proc_attach_tgid_threads): New declaration.
	* nat/linux-ptrace.c (linux_ptrace_attach_fail_reason): Adjust to
	use nowarn functions.
	(linux_ptrace_attach_fail_reason_string): Move here from
	gdbserver/linux-low.c and rename.
	(ptrace_supports_feature): If the current ptrace options are not
	known yet, check them now, instead of asserting.
	* nat/linux-ptrace.h (linux_ptrace_attach_fail_reason_string):
	Declare.
This commit is contained in:
Pedro Alves 2014-12-16 16:12:24 +00:00
parent 883ed13e4a
commit 8784d56326
11 changed files with 406 additions and 127 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

40
gdb/ChangeLog
View File

@ -1,3 +1,43 @@
2015-01-09 Pedro Alves <palves@redhat.com>
* linux-nat.c (attach_proc_task_lwp_callback): New function.
(linux_nat_attach): Use linux_proc_attach_tgid_threads.
(wait_lwp, linux_nat_filter_event): If not set yet, set the lwp's
ptrace option flags.
* linux-nat.h (struct lwp_info) <must_set_ptrace_flags>: New
field.
* nat/linux-procfs.c: Include <dirent.h>.
(linux_proc_get_int): New parameter "warn". Handle it.
(linux_proc_get_tgid): Adjust.
(linux_proc_get_tracerpid): Rename to ...
(linux_proc_get_tracerpid_nowarn): ... this.
(linux_proc_pid_get_state): New function, factored out from
(linux_proc_pid_has_state): ... this. Add new parameter "warn"
and handle it.
(linux_proc_pid_is_gone): New function.
(linux_proc_pid_is_stopped): Adjust.
(linux_proc_pid_is_zombie_maybe_warn)
(linux_proc_pid_is_zombie_nowarn): New functions.
(linux_proc_pid_is_zombie): Use
linux_proc_pid_is_zombie_maybe_warn.
(linux_proc_attach_tgid_threads): New function.
* nat/linux-procfs.h (linux_proc_get_tgid): Update comment.
(linux_proc_get_tracerpid): Rename to ...
(linux_proc_get_tracerpid_nowarn): ... this, and update comment.
(linux_proc_pid_is_gone): New declaration.
(linux_proc_pid_is_zombie): Update comment.
(linux_proc_pid_is_zombie_nowarn): New declaration.
(linux_proc_attach_lwp_func): New typedef.
(linux_proc_attach_tgid_threads): New declaration.
* nat/linux-ptrace.c (linux_ptrace_attach_fail_reason): Adjust to
use nowarn functions.
(linux_ptrace_attach_fail_reason_string): Move here from
gdbserver/linux-low.c and rename.
(ptrace_supports_feature): If the current ptrace options are not
known yet, check them now, instead of asserting.
* nat/linux-ptrace.h (linux_ptrace_attach_fail_reason_string):
Declare.
2015-01-09 Pedro Alves <palves@redhat.com>
* linux-thread-db.c (thread_db_find_new_threads_silently)

10
gdb/gdbserver/ChangeLog
View File

@ -1,3 +1,13 @@
2015-01-09 Pedro Alves <palves@redhat.com>
* linux-low.c (linux_attach_fail_reason_string): Move to
nat/linux-ptrace.c, and rename.
(linux_attach_lwp): Update comment.
(attach_proc_task_lwp_callback): New function.
(linux_attach): Adjust to rename and use
linux_proc_attach_tgid_threads.
(linux_attach_fail_reason_string): Delete declaration.
2015-01-01 Joel Brobecker <brobecker@adacore.com>
* gdbreplay.c (gdbreplay_version): Update copyright year to 2015.

152
gdb/gdbserver/linux-low.c
View File

@ -631,31 +631,8 @@ linux_create_inferior (char *program, char **allargs)
return pid;
}
char *
linux_attach_fail_reason_string (ptid_t ptid, int err)
{
static char *reason_string;
struct buffer buffer;
char *warnings;
long lwpid = ptid_get_lwp (ptid);
xfree (reason_string);
buffer_init (&buffer);
linux_ptrace_attach_fail_reason (lwpid, &buffer);
buffer_grow_str0 (&buffer, "");
warnings = buffer_finish (&buffer);
if (warnings[0] != '\0')
reason_string = xstrprintf ("%s (%d), %s",
strerror (err), err, warnings);
else
reason_string = xstrprintf ("%s (%d)",
strerror (err), err);
xfree (warnings);
return reason_string;
}
/* Attach to an inferior process. */
/* Attach to an inferior process. Returns 0 on success, ERRNO on
error. */
int
linux_attach_lwp (ptid_t ptid)
@ -739,6 +716,50 @@ linux_attach_lwp (ptid_t ptid)
return 0;
}
/* Callback for linux_proc_attach_tgid_threads. Attach to PTID if not
already attached. Returns true if a new LWP is found, false
otherwise. */
static int
attach_proc_task_lwp_callback (ptid_t ptid)
{
/* Is this a new thread? */
if (find_thread_ptid (ptid) == NULL)
{
int lwpid = ptid_get_lwp (ptid);
int err;
if (debug_threads)
debug_printf ("Found new lwp %d\n", lwpid);
err = linux_attach_lwp (ptid);
/* Be quiet if we simply raced with the thread exiting. EPERM
is returned if the thread's task still exists, and is marked
as exited or zombie, as well as other conditions, so in that
case, confirm the status in /proc/PID/status. */
if (err == ESRCH
|| (err == EPERM && linux_proc_pid_is_gone (lwpid)))
{
if (debug_threads)
{
debug_printf ("Cannot attach to lwp %d: "
"thread is gone (%d: %s)\n",
lwpid, err, strerror (err));
}
}
else if (err != 0)
{
warning (_("Cannot attach to lwp %d: %s"),
lwpid,
linux_ptrace_attach_fail_reason_string (ptid, err));
}
return 1;
}
return 0;
}
/* Attach to PID. If PID is the tgid, attach to it and all
of its threads. */
@ -753,7 +774,7 @@ linux_attach (unsigned long pid)
err = linux_attach_lwp (ptid);
if (err != 0)
error ("Cannot attach to process %ld: %s",
pid, linux_attach_fail_reason_string (ptid, err));
pid, linux_ptrace_attach_fail_reason_string (ptid, err));
linux_add_process (pid, 1);
@ -767,75 +788,16 @@ linux_attach (unsigned long pid)
thread->last_resume_kind = resume_stop;
}
if (linux_proc_get_tgid (pid) == pid)
{
DIR *dir;
char pathname[128];
sprintf (pathname, "/proc/%ld/task", pid);
dir = opendir (pathname);
if (!dir)
{
fprintf (stderr, "Could not open /proc/%ld/task.\n", pid);
fflush (stderr);
}
else
{
/* At this point we attached to the tgid. Scan the task for
existing threads. */
int new_threads_found;
int iterations = 0;
while (iterations < 2)
{
struct dirent *dp;
new_threads_found = 0;
/* Add all the other threads. While we go through the
threads, new threads may be spawned. Cycle through
the list of threads until we have done two iterations without
finding new threads. */
while ((dp = readdir (dir)) != NULL)
{
unsigned long lwp;
ptid_t ptid;
/* Fetch one lwp. */
lwp = strtoul (dp->d_name, NULL, 10);
ptid = ptid_build (pid, lwp, 0);
/* Is this a new thread? */
if (lwp != 0 && find_thread_ptid (ptid) == NULL)
{
int err;
if (debug_threads)
debug_printf ("Found new lwp %ld\n", lwp);
err = linux_attach_lwp (ptid);
if (err != 0)
warning ("Cannot attach to lwp %ld: %s",
lwp,
linux_attach_fail_reason_string (ptid, err));
new_threads_found++;
}
}
if (!new_threads_found)
iterations++;
else
iterations = 0;
rewinddir (dir);
}
closedir (dir);
}
}
/* We must attach to every LWP. If /proc is mounted, use that to
find them now. On the one hand, the inferior may be using raw
clone instead of using pthreads. On the other hand, even if it
is using pthreads, GDB may not be connected yet (thread_db needs
to do symbol lookups, through qSymbol). Also, thread_db walks
structures in the inferior's address space to find the list of
threads/LWPs, and those structures may well be corrupted. Note
that once thread_db is loaded, we'll still use it to list threads
and associate pthread info with each LWP. */
linux_proc_attach_tgid_threads (pid, attach_proc_task_lwp_callback);
return 0;
}

6
gdb/gdbserver/linux-low.h
View File

@ -351,12 +351,6 @@ int linux_pid_exe_is_elf_64_file (int pid, unsigned int *machine);
errno). */
int linux_attach_lwp (ptid_t ptid);
/* Return the reason an attach failed, in string form. ERR is the
error returned by linux_attach_lwp (an errno). This string should
be copied into a buffer by the client if the string will not be
immediately used, or if it must persist. */
char *linux_attach_fail_reason_string (ptid_t ptid, int err);
struct lwp_info *find_lwp_pid (ptid_t ptid);
void linux_stop_lwp (struct lwp_info *lwp);

2
gdb/gdbserver/thread-db.c
View File

@ -339,7 +339,7 @@ attach_thread (const td_thrhandle_t *th_p, td_thrinfo_t *ti_p)
{
warning ("Could not attach to thread %ld (LWP %d): %s\n",
ti_p->ti_tid, ti_p->ti_lid,
linux_attach_fail_reason_string (ptid, err));
linux_ptrace_attach_fail_reason_string (ptid, err));
return 0;
}

93
gdb/linux-nat.c
View File

@ -1137,6 +1137,73 @@ linux_nat_create_inferior (struct target_ops *ops,
#endif /* HAVE_PERSONALITY */
}
/* Callback for linux_proc_attach_tgid_threads. Attach to PTID if not
already attached. Returns true if a new LWP is found, false
otherwise. */
static int
attach_proc_task_lwp_callback (ptid_t ptid)
{
struct lwp_info *lp;
/* Ignore LWPs we're already attached to. */
lp = find_lwp_pid (ptid);
if (lp == NULL)
{
int lwpid = ptid_get_lwp (ptid);
if (ptrace (PTRACE_ATTACH, lwpid, 0, 0) < 0)
{
int err = errno;
/* Be quiet if we simply raced with the thread exiting.
EPERM is returned if the thread's task still exists, and
is marked as exited or zombie, as well as other
conditions, so in that case, confirm the status in
/proc/PID/status. */
if (err == ESRCH
|| (err == EPERM && linux_proc_pid_is_gone (lwpid)))
{
if (debug_linux_nat)
{
fprintf_unfiltered (gdb_stdlog,
"Cannot attach to lwp %d: "
"thread is gone (%d: %s)\n",
lwpid, err, safe_strerror (err));
}
}
else
{
warning (_("Cannot attach to lwp %d: %s\n"),
lwpid,
linux_ptrace_attach_fail_reason_string (ptid,
err));
}
}
else
{
if (debug_linux_nat)
fprintf_unfiltered (gdb_stdlog,
"PTRACE_ATTACH %s, 0, 0 (OK)\n",
target_pid_to_str (ptid));
lp = add_lwp (ptid);
lp->cloned = 1;
/* The next time we wait for this LWP we'll see a SIGSTOP as
PTRACE_ATTACH brings it to a halt. */
lp->signalled = 1;
/* We need to wait for a stop before being able to make the
next ptrace call on this LWP. */
lp->must_set_ptrace_flags = 1;
}
return 1;
}
return 0;
}
static void
linux_nat_attach (struct target_ops *ops, const char *args, int from_tty)
{
@ -1230,6 +1297,16 @@ linux_nat_attach (struct target_ops *ops, const char *args, int from_tty)
lp->status = status;
/* We must attach to every LWP. If /proc is mounted, use that to
find them now. The inferior may be using raw clone instead of
using pthreads. But even if it is using pthreads, thread_db
walks structures in the inferior's address space to find the list
of threads/LWPs, and those structures may well be corrupted.
Note that once thread_db is loaded, we'll still use it to list
threads and associate pthread info with each LWP. */
linux_proc_attach_tgid_threads (ptid_get_pid (lp->ptid),
attach_proc_task_lwp_callback);
if (target_can_async_p ())
target_async (inferior_event_handler, 0);
}
@ -2159,6 +2236,14 @@ wait_lwp (struct lwp_info *lp)
gdb_assert (WIFSTOPPED (status));
lp->stopped = 1;
if (lp->must_set_ptrace_flags)
{
struct inferior *inf = find_inferior_pid (ptid_get_pid (lp->ptid));
linux_enable_event_reporting (ptid_get_lwp (lp->ptid), inf->attach_flag);
lp->must_set_ptrace_flags = 0;
}
/* Handle GNU/Linux's syscall SIGTRAPs. */
if (WIFSTOPPED (status) && WSTOPSIG (status) == SYSCALL_SIGTRAP)
{
@ -2783,6 +2868,14 @@ linux_nat_filter_event (int lwpid, int status, int *new_pending_p)
ever being continued.) */
lp->stopped = 1;
if (WIFSTOPPED (status) && lp->must_set_ptrace_flags)
{
struct inferior *inf = find_inferior_pid (ptid_get_pid (lp->ptid));
linux_enable_event_reporting (ptid_get_lwp (lp->ptid), inf->attach_flag);
lp->must_set_ptrace_flags = 0;
}
/* Handle GNU/Linux's syscall SIGTRAPs. */
if (WIFSTOPPED (status) && WSTOPSIG (status) == SYSCALL_SIGTRAP)
{

4
gdb/linux-nat.h
View File

@ -33,6 +33,10 @@ struct lwp_info
and overall process id. */
ptid_t ptid;
/* If this flag is set, we need to set the event request flags the
next time we see this LWP stop. */
int must_set_ptrace_flags;
/* Non-zero if this LWP is cloned. In this context "cloned" means
that the LWP is reporting to its parent using a signal other than
SIGCHLD. */

153
gdb/nat/linux-procfs.c
View File

@ -19,12 +19,13 @@
#include "common-defs.h"
#include "linux-procfs.h"
#include "filestuff.h"
#include <dirent.h>
/* Return the TGID of LWPID from /proc/pid/status. Returns -1 if not
found. */
static int
linux_proc_get_int (pid_t lwpid, const char *field)
linux_proc_get_int (pid_t lwpid, const char *field, int warn)
{
size_t field_len = strlen (field);
FILE *status_file;
@ -35,7 +36,8 @@ linux_proc_get_int (pid_t lwpid, const char *field)
status_file = gdb_fopen_cloexec (buf, "r");
if (status_file == NULL)
{
warning (_("unable to open /proc file '%s'"), buf);
if (warn)
warning (_("unable to open /proc file '%s'"), buf);
return -1;
}
@ -56,45 +58,87 @@ linux_proc_get_int (pid_t lwpid, const char *field)
int
linux_proc_get_tgid (pid_t lwpid)
{
return linux_proc_get_int (lwpid, "Tgid");
return linux_proc_get_int (lwpid, "Tgid", 1);
}
/* See linux-procfs.h. */
pid_t
linux_proc_get_tracerpid (pid_t lwpid)
linux_proc_get_tracerpid_nowarn (pid_t lwpid)
{
return linux_proc_get_int (lwpid, "TracerPid");
return linux_proc_get_int (lwpid, "TracerPid", 0);
}
/* Return non-zero if 'State' of /proc/PID/status contains STATE. */
/* Fill in BUFFER, a buffer with BUFFER_SIZE bytes with the 'State'
line of /proc/PID/status. Returns -1 on failure to open the /proc
file, 1 if the line is found, and 0 if not found. If WARN, warn on
failure to open the /proc file. */
static int
linux_proc_pid_has_state (pid_t pid, const char *state)
linux_proc_pid_get_state (pid_t pid, char *buffer, size_t buffer_size,
int warn)
{
char buffer[100];
FILE *procfile;
int retval;
int have_state;
xsnprintf (buffer, sizeof (buffer), "/proc/%d/status", (int) pid);
xsnprintf (buffer, buffer_size, "/proc/%d/status", (int) pid);
procfile = gdb_fopen_cloexec (buffer, "r");
if (procfile == NULL)
{
warning (_("unable to open /proc file '%s'"), buffer);
return 0;
if (warn)
warning (_("unable to open /proc file '%s'"), buffer);
return -1;
}
have_state = 0;
while (fgets (buffer, sizeof (buffer), procfile) != NULL)
while (fgets (buffer, buffer_size, procfile) != NULL)
if (strncmp (buffer, "State:", 6) == 0)
{
have_state = 1;
break;
}
retval = (have_state && strstr (buffer, state) != NULL);
fclose (procfile);
return retval;
return have_state;
}
/* See linux-procfs.h declaration. */
int
linux_proc_pid_is_gone (pid_t pid)
{
char buffer[100];
int have_state;
have_state = linux_proc_pid_get_state (pid, buffer, sizeof buffer, 0);
if (have_state < 0)
{
/* If we can't open the status file, assume the thread has
disappeared. */
return 1;
}
else if (have_state == 0)
{
/* No "State:" line, assume thread is alive. */
return 0;
}
else
{
return (strstr (buffer, "Z (") != NULL
|| strstr (buffer, "X (") != NULL);
}
}
/* Return non-zero if 'State' of /proc/PID/status contains STATE. If
WARN, warn on failure to open the /proc file. */
static int
linux_proc_pid_has_state (pid_t pid, const char *state, int warn)
{
char buffer[100];
int have_state;
have_state = linux_proc_pid_get_state (pid, buffer, sizeof buffer, warn);
return (have_state > 0 && strstr (buffer, state) != NULL);
}
/* Detect `T (stopped)' in `/proc/PID/status'.
@ -103,7 +147,24 @@ linux_proc_pid_has_state (pid_t pid, const char *state)
int
linux_proc_pid_is_stopped (pid_t pid)
{
return linux_proc_pid_has_state (pid, "T (stopped)");
return linux_proc_pid_has_state (pid, "T (stopped)", 1);
}
/* Return non-zero if PID is a zombie. If WARN, warn on failure to
open the /proc file. */
static int
linux_proc_pid_is_zombie_maybe_warn (pid_t pid, int warn)
{
return linux_proc_pid_has_state (pid, "Z (zombie)", warn);
}
/* See linux-procfs.h declaration. */
int
linux_proc_pid_is_zombie_nowarn (pid_t pid)
{
return linux_proc_pid_is_zombie_maybe_warn (pid, 0);
}
/* See linux-procfs.h declaration. */
@ -111,7 +172,7 @@ linux_proc_pid_is_stopped (pid_t pid)
int
linux_proc_pid_is_zombie (pid_t pid)
{
return linux_proc_pid_has_state (pid, "Z (zombie)");
return linux_proc_pid_is_zombie_maybe_warn (pid, 1);
}
/* See linux-procfs.h declaration. */
@ -132,3 +193,61 @@ linux_proc_pid_get_ns (pid_t pid, const char *ns)
return NULL;
}
/* See linux-procfs.h. */
void
linux_proc_attach_tgid_threads (pid_t pid,
linux_proc_attach_lwp_func attach_lwp)
{
DIR *dir;
char pathname[128];
int new_threads_found;
int iterations;
if (linux_proc_get_tgid (pid) != pid)
return;
xsnprintf (pathname, sizeof (pathname), "/proc/%ld/task", (long) pid);
dir = opendir (pathname);
if (dir == NULL)
{
warning (_("Could not open /proc/%ld/task.\n"), (long) pid);
return;
}
/* Scan the task list for existing threads. While we go through the
threads, new threads may be spawned. Cycle through the list of
threads until we have done two iterations without finding new
threads. */
for (iterations = 0; iterations < 2; iterations++)
{
struct dirent *dp;
new_threads_found = 0;
while ((dp = readdir (dir)) != NULL)
{
unsigned long lwp;
/* Fetch one lwp. */
lwp = strtoul (dp->d_name, NULL, 10);
if (lwp != 0)
{
ptid_t ptid = ptid_build (pid, lwp, 0);
if (attach_lwp (ptid))
new_threads_found = 1;
}
}
if (new_threads_found)
{
/* Start over. */
iterations = -1;
}
rewinddir (dir);
}
closedir (dir);
}

32
gdb/nat/linux-procfs.h
View File

@ -22,28 +22,50 @@
#include <unistd.h>
/* Return the TGID of LWPID from /proc/pid/status. Returns -1 if not
found. */
found. Failure to open the /proc file results in a warning. */
extern int linux_proc_get_tgid (pid_t lwpid);
/* Return the TracerPid of LWPID from /proc/pid/status. Returns -1 if not
found. */
/* Return the TracerPid of LWPID from /proc/pid/status. Returns -1 if
not found. Does not warn on failure to open the /proc file. */
extern pid_t linux_proc_get_tracerpid (pid_t lwpid);
extern pid_t linux_proc_get_tracerpid_nowarn (pid_t lwpid);
/* Detect `T (stopped)' in `/proc/PID/status'.
Other states including `T (tracing stop)' are reported as false. */
extern int linux_proc_pid_is_stopped (pid_t pid);
/* Return non-zero if PID is a zombie. */
/* Return non-zero if PID is a zombie. Failure to open the
/proc/pid/status file results in a warning. */
extern int linux_proc_pid_is_zombie (pid_t pid);
/* Return non-zero if PID is a zombie. Does not warn on failure to
open the /proc file. */
extern int linux_proc_pid_is_zombie_nowarn (pid_t pid);
/* Return non-zero if /proc/PID/status indicates that PID is gone
(i.e., in Z/Zombie or X/Dead state). Failure to open the /proc
file is assumed to indicate the thread is gone. */
extern int linux_proc_pid_is_gone (pid_t pid);
/* Return an opaque string identifying PID's NS namespace or NULL if
* the information is unavailable. The returned string must be
* released with xfree. */
extern char *linux_proc_pid_get_ns (pid_t pid, const char *ns);
/* Callback function for linux_proc_attach_tgid_threads. If the PTID
thread is not yet known, try to attach to it and return true,
otherwise return false. */
typedef int (*linux_proc_attach_lwp_func) (ptid_t ptid);
/* If PID is a tgid, scan the /proc/PID/task/ directory for existing
threads, and call FUNC for each thread found. */
extern void linux_proc_attach_tgid_threads (pid_t pid,
linux_proc_attach_lwp_func func);
#endif /* COMMON_LINUX_PROCFS_H */

33
gdb/nat/linux-ptrace.c
View File

@ -43,18 +43,44 @@ linux_ptrace_attach_fail_reason (pid_t pid, struct buffer *buffer)
{
pid_t tracerpid;
tracerpid = linux_proc_get_tracerpid (pid);
tracerpid = linux_proc_get_tracerpid_nowarn (pid);
if (tracerpid > 0)
buffer_xml_printf (buffer, _("process %d is already traced "
"by process %d"),
(int) pid, (int) tracerpid);
if (linux_proc_pid_is_zombie (pid))
if (linux_proc_pid_is_zombie_nowarn (pid))
buffer_xml_printf (buffer, _("process %d is a zombie "
"- the process has already terminated"),
(int) pid);
}
/* See linux-ptrace.h. */
char *
linux_ptrace_attach_fail_reason_string (ptid_t ptid, int err)
{
static char *reason_string;
struct buffer buffer;
char *warnings;
long lwpid = ptid_get_lwp (ptid);
xfree (reason_string);
buffer_init (&buffer);
linux_ptrace_attach_fail_reason (lwpid, &buffer);
buffer_grow_str0 (&buffer, "");
warnings = buffer_finish (&buffer);
if (warnings[0] != '\0')
reason_string = xstrprintf ("%s (%d), %s",
strerror (err), err, warnings);
else
reason_string = xstrprintf ("%s (%d)",
strerror (err), err);
xfree (warnings);
return reason_string;
}
#if defined __i386__ || defined __x86_64__
/* Address of the 'ret' instruction in asm code block below. */
@ -508,7 +534,8 @@ linux_disable_event_reporting (pid_t pid)
static int
ptrace_supports_feature (int ptrace_options)
{
gdb_assert (current_ptrace_options >= 0);
if (current_ptrace_options == -1)
linux_check_ptrace_features ();
return ((current_ptrace_options & ptrace_options) == ptrace_options);
}

8
gdb/nat/linux-ptrace.h
View File

@ -89,6 +89,14 @@ struct buffer;
#endif
extern void linux_ptrace_attach_fail_reason (pid_t pid, struct buffer *buffer);
/* Find all possible reasons we could have failed to attach to PTID
and return them as a string. ERR is the error PTRACE_ATTACH failed
with (an errno). The result is stored in a static buffer. This
string should be copied into a buffer by the client if the string
will not be immediately used, or if it must persist. */
extern char *linux_ptrace_attach_fail_reason_string (ptid_t ptid, int err);
extern void linux_ptrace_init_warnings (void);
extern void linux_enable_event_reporting (pid_t pid, int attached);
extern void linux_disable_event_reporting (pid_t pid);