Re: [patch] Fix Linux attach to signalled/stopped processes

Jan Kratochvil
2007-07-01T10:03:19Z

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On Sun, 01 Jul 2007 11:34:05 +0200, Mark Kettenis wrote:
...
> > Then all we need is a trivial change like this:
> >
> > On GNU/Linux, stopped processes may get attached now. Signals being
> > delivered at the time of the attach command no longer get lost.
>
> Fine with me.

Fixed, reattached; although some ptrace(2) review/approval is still needed.

Regards,
Jan

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2007-07-01 Jan Kratochvil <jan.kratochvil@redhat.com>

* linux-nat.h (struct lwp_info): New field WAS_STOPPED.
* linux-nat.c (STRINGIFY, STRINGIFY_ARG): New macros.
(kill_lwp): New declaration.
(linux_ptrace_post_attach, pid_is_stopped): New function.
(linux_child_follow_fork): New comment about WAS_STOPPED.
(lin_lwp_attach_lwp): Variable PID removed. Part replaced by a call to
LINUX_PTRACE_POST_ATTACH.
(linux_nat_attach): Likewise.
(linux_nat_detach): Optionally stop the detached process.
(linux_nat_resume): Clear WAS_STOPPED if appropriate.
* NEWS: Document the new behaviour.

2007-06-30 Jan Kratochvil <jan.kratochvil@redhat.com>

* gdb.threads/attach-into-signal.c, gdb.threads/attach-into-signal.exp,
gdb.threads/attach-stopped.c, gdb.threads/attach-stopped.exp: New files.

2007-06-30 Jan Kratochvil <jan.kratochvil@redhat.com>

* gdb.texinfo (Attach): Document the ATTACH and DETACH commands for
stopped processes. Document the messages on the seen pending signals.

--- ./gdb/NEWS 21 Jun 2007 15:18:50 -0000 1.232
+++ ./gdb/NEWS 30 Jun 2007 16:27:37 -0000
@@ -44,6 +44,9 @@ segment base addresses (rather than offs
* The /i format now outputs any trailing branch delay slot instructions
immediately following the last instruction within the count specified.

+* On GNU/Linux, stopped processes may get attached to now. Signals being
+delivered at the time of the attach command no longer get lost.
+
* New commands

set remoteflow
--- ./gdb/linux-nat.c 16 Jun 2007 17:16:25 -0000 1.64
+++ ./gdb/linux-nat.c 29 Jun 2007 22:06:05 -0000
@@ -86,6 +86,12 @@
#define __WALL 0x40000000 /* Wait for any child. */
#endif

+#define STRINGIFY_ARG(x) #x
+#define STRINGIFY(x) STRINGIFY_ARG (x)
+
+static int linux_ptrace_post_attach (struct lwp_info *lp);
+static int kill_lwp (int lwpid, int signo);
+
/* The single-threaded native GNU/Linux target_ops. We save a pointer for
the use of the multi-threaded target. */
static struct target_ops *linux_ops;
@@ -502,6 +508,11 @@ linux_child_follow_fork (struct target_o
}
else
{
+ /* We should check LP->WAS_STOPPED and detach it stopped accordingly.
+ In this point of code it cannot be 1 as we would not get FORK
+ executed without CONTINUE first which resets LP->WAS_STOPPED.
+ We would have to first TARGET_STOP and WAITPID it as with running
+ inferior PTRACE_DETACH, SIGSTOP will ignore the signal. */
target_detach (NULL, 0);
}

@@ -884,7 +895,6 @@ lin_lwp_attach_lwp (ptid_t ptid, int ver
to happen. */
if (GET_LWP (ptid) != GET_PID (ptid) && lp == NULL)
{
- pid_t pid;
int status;

if (ptrace (PTRACE_ATTACH, GET_LWP (ptid), 0, 0) < 0)
@@ -902,33 +912,17 @@ lin_lwp_attach_lwp (ptid_t ptid, int ver
if (lp == NULL)
lp = add_lwp (ptid);

- if (debug_linux_nat)
- fprintf_unfiltered (gdb_stdlog,
- "LLAL: PTRACE_ATTACH %s, 0, 0 (OK)\n",
- target_pid_to_str (ptid));
-
- pid = my_waitpid (GET_LWP (ptid), &status, 0);
- if (pid == -1 && errno == ECHILD)
- {
- /* Try again with __WCLONE to check cloned processes. */
- pid = my_waitpid (GET_LWP (ptid), &status, __WCLONE);
- lp->cloned = 1;
+ status = linux_ptrace_post_attach (lp);
+ if (status != 0)
+ {
+ warning (_("Thread %s exited: %s"), target_pid_to_str (ptid),
+ status_to_str (status));
+ return -1;
}

- gdb_assert (pid == GET_LWP (ptid)
- && WIFSTOPPED (status) && WSTOPSIG (status));
-
- target_post_attach (pid);
+ target_post_attach (GET_LWP (ptid));

lp->stopped = 1;
-
- if (debug_linux_nat)
- {
- fprintf_unfiltered (gdb_stdlog,
- "LLAL: waitpid %s received %s\n",
- target_pid_to_str (ptid),
- status_to_str (status));
- }
}
else
{
@@ -949,11 +943,172 @@ lin_lwp_attach_lwp (ptid_t ptid, int ver
return 0;
}

+/* Detect `T (stopped)' in `/proc/PID/status'.
+ Other states including `T (tracing stop)' are reported as false. */
+
+static int
+pid_is_stopped (pid_t pid)
+{
+ FILE *status_file;
+ char buf[100];
+ int retval = 0;
+
+ snprintf (buf, sizeof (buf), "/proc/%d/status", (int) pid);
+ status_file = fopen (buf, "r");
+ if (status_file != NULL)
+ {
+ int have_state = 0;
+
+ while (fgets (buf, sizeof (buf), status_file))
+ {
+ if (strncmp (buf, "State:", 6) == 0)
+ {
+ have_state = 1;
+ break;
+ }
+ }
+ if (have_state && strstr (buf, "T (stopped)") != NULL)
+ retval = 1;
+ fclose (status_file);
+ }
+ return retval;
+}
+
+/* Handle the processing after PTRACE_ATTACH, the first WAITPID -> SIGSTOP.
+ Returns STATUS if the thread has exited, 0 otherwise.
+ Sets LP->WAS_STOPPED if the process was originally stopped.
+ Sets LP->CLONED if the given LWP is not the thread leader.
+
+ Scenario for a standard unstopped inferior:
+ * `S (sleeping)' or `R (running)' or similiar states.
+ * PTRACE_ATTACH is called.
+ * `S (sleeping)' (or similiar) for some while.
+ * `T (tracing stop)'.
+ * WAITPID succeeds here returning SIGSTOP (signalled by PTRACE_ATTACH).
+
+ Scenario for a formerly stopped inferior:
+ * `T (stopped)'.
+ * PTRACE_ATTACH is called.
+ * `T (stopped)' would stay indefinitely
+ Note since this moment the `TracerPid' field gets filled
+ (by PTRACE_ATTACH), it is no longer just the common `T (stopped)' state.
+ * If no one did WAITPID since sending SIGSTOP our WAITPID would return
+ SIGSTOP. The state still would not turn to `T (tracing stop)'.
+ * Usually its original parent (before PTRACE_ATTACH was applied) already
+ did WAITPID. The original parent already received our SIGSTOP
+ sinalled by our PTRACE_ATTACH.
+ In this case our own WAITPID would hang. Therefore...
+ * ... we do artificial: tkill (SIGCONT);
+ `PTRACE_CONT, SIGSTOP' does not work in 100% cases as sometimes SIGSTOP
+ gets remembered by kernel during the first PTRACE_CONT later and we get
+ spurious SIGSTOP event. Expecting the signal may get delivered to
+ a different task of the thread group.
+ `kill_lwp (SIGSTOP)' has no effect in this moment (it is already stopped).
+ * WAITPID returns the artifical SIGCONT.
+ (The possibly pending SIGSTOP gets vanished by specifically SIGCONT.)
+ * State turns `T (tracing stop)'.
+ In this moment everything is almost fine but we need a workaround as final
+ `PTRACE_DETACH, SIGSTOP' would leave the process unstopped otherwise:
+ * tkill (SIGSTOP);
+ * `PTRACE_CONT, 0'
+ * WAITPID returns the artifical SIGSTOP.
+
+ With the pending (unwaited for) SIGSTOP the artifical signal effects are:
+ kill (SIGSTOP)
+ PTRACE_ATTACH
+ /-tkill (SIGCONT), WAITPID: SIGCONT, WAITPID: hang !
+ //-tkill (SIGCONT), WAITPID: SIGCONT, PTRACE_CONT (SIG_0), WAITPID: wait (OK)
+ \\-tkill (SIGALRM), WAITPID: SIGSTOP, WAITPID: hang !
+ \-tkill (SIGALRM), WAITPID: SIGSTOP, PTRACE_CONT (SIG_0), WAITPID: SIGALRM !
+ Therefore we signal artifical SIGCONT and stop waiting after its reception.
+
+ For the detection whether the process was formerly stopped we need to
+ read `/proc/PID/status'. `PTRACE_CONT, SIGSTOP' returns ESRCH
+ for `S (sleeping)' and succeeds for `T (stopped)' but it unfortunately
+ succeeds even for `T (tracing stop)'. Depending on PTRACE_CONT, SIGSTOP
+ success value for formerly stopped processes would mean a race condition
+ as we would get false stopped processes detection if we get too slow.
+
+ `waitid (..., WSTOPPED)' hangs the same way as WAITPID.
+
+ Signals get queued for WAITPID. PTRACE_ATTACH (or TKILL) enqueues SIGSTOP
+ there but WAITPID may return an already pending signal.
+ Redeliver it by PTRACE_CONT, SIGxxx as otherwise it would get lost.
+ Similiar processing is being done in this file by WAIT_LWP. */
+
+static int
+linux_ptrace_post_attach (struct lwp_info *lp)
+{
+ ptid_t ptid = lp->ptid;
+ unsigned long sig;
+
+ if (debug_linux_nat)
+ fprintf_unfiltered (gdb_stdlog,
+ "LLAL: PTRACE_ATTACH %s, 0, 0 (OK)\n",
+ target_pid_to_str (ptid));
+
+ lp->was_stopped = pid_is_stopped (GET_LWP (ptid));
+ if (lp->was_stopped)
+ {
+ if (kill_lwp (GET_LWP (ptid), SIGCONT) != 0)
+ perror_with_name (("kill_lwp (SIGCONT)"));
+ }
+
+ for (;;)
+ {
+ pid_t pid;
+ int status;
+
+ pid = my_waitpid (GET_LWP (ptid), &status, 0);
+ if (pid == -1 && errno == ECHILD)
+ {
+ /* Try again with __WCLONE to check cloned processes. */
+ pid = my_waitpid (GET_LWP (ptid), &status, __WCLONE);
+ lp->cloned = 1;
+ }
+ gdb_assert (pid == GET_LWP (ptid));
+
+ if (debug_linux_nat)
+ {
+ fprintf_unfiltered (gdb_stdlog,
+ "LLAL: waitpid %s received %s\n",
+ target_pid_to_str (ptid),
+ status_to_str (status));
+ }
+
+ /* Check if the thread has exited. */
+ if (WIFEXITED (status) || WIFSIGNALED (status))
+ return status;
+ gdb_assert (WIFSTOPPED (status));
+ sig = WSTOPSIG (status);
+ gdb_assert (sig != 0);
+ if (sig == SIGSTOP)
+ break;
+
+ /* As the second signal for stopped processes we send SIGSTOP. */
+ if (lp->was_stopped && sig == SIGCONT)
+ sig = SIGSTOP;
+
+ printf_unfiltered (_("Redelivering pending %s.\n"),
+ target_signal_to_string (target_signal_from_host (sig)));
+ if (sig == SIGSTOP)
+ {
+ if (kill_lwp (GET_LWP (ptid), sig) != 0)
+ perror_with_name (("kill_lwp"));
+ /* We now must resume the inferior to get SIGSTOP delivered. */
+ sig = 0;
+ }
+ if (ptrace (PTRACE_CONT, GET_LWP (ptid), NULL, (void *) sig) != 0)
+ perror_with_name (("ptrace"));
+ }
+
+ return 0;
+}
+
static void
linux_nat_attach (char *args, int from_tty)
{
struct lwp_info *lp;
- pid_t pid;
int status;

/* FIXME: We should probably accept a list of process id's, and
@@ -964,21 +1122,12 @@ linux_nat_attach (char *args, int from_t
inferior_ptid = BUILD_LWP (GET_PID (inferior_ptid), GET_PID (inferior_ptid));
lp = add_lwp (inferior_ptid);

- /* Make sure the initial process is stopped. The user-level threads
- layer might want to poke around in the inferior, and that won't
- work if things haven't stabilized yet. */
- pid = my_waitpid (GET_PID (inferior_ptid), &status, 0);
- if (pid == -1 && errno == ECHILD)
- {
- warning (_("%s is a cloned process"), target_pid_to_str (inferior_ptid));
-
- /* Try again with __WCLONE to check cloned processes. */
- pid = my_waitpid (GET_PID (inferior_ptid), &status, __WCLONE);
- lp->cloned = 1;
- }
-
- gdb_assert (pid == GET_PID (inferior_ptid)
- && WIFSTOPPED (status) && WSTOPSIG (status) == SIGSTOP);
+ status = linux_ptrace_post_attach (lp);
+ if (status != 0)
+ error (_("Program %s exited: %s\n"), target_pid_to_str (inferior_ptid),
+ status_to_str (status));
+ if (lp->cloned)
+ warning (_("%s is a cloned process"), target_pid_to_str (inferior_ptid));

lp->stopped = 1;

@@ -987,8 +1136,8 @@ linux_nat_attach (char *args, int from_t
lp->resumed = 1;
if (debug_linux_nat)
{
- fprintf_unfiltered (gdb_stdlog,
- "LLA: waitpid %ld, faking SIGSTOP\n", (long) pid);
+ fprintf_unfiltered (gdb_stdlog, "LLA: waitpid %d, faking SIGSTOP\n",
+ GET_PID (inferior_ptid));
}
}

@@ -1061,6 +1210,9 @@ linux_nat_detach (char *args, int from_t

trap_ptid = null_ptid;

+ if (lwp_list->was_stopped)
+ args = STRINGIFY (SIGSTOP);
+
/* Destroy LWP info; it's no longer valid. */
init_lwp_list ();

@@ -1196,6 +1348,12 @@ linux_nat_resume (ptid_t ptid, int step,
lp->stopped = 0;
}

+ /* At this point, we are going to resume the inferior and if we
+ have attached to a stopped process, we no longer should leave
+ it as stopped if the user detaches. */
+ if (!step && lp != NULL)
+ lp->was_stopped = 0;
+
if (resume_all)
iterate_over_lwps (resume_callback, NULL);

--- ./gdb/linux-nat.h 10 May 2007 21:36:00 -0000 1.18
+++ ./gdb/linux-nat.h 29 Jun 2007 22:06:05 -0000
@@ -42,6 +42,9 @@ struct lwp_info
/* Non-zero if this LWP is stopped. */
int stopped;

+ /* Non-zero if this LWP was stopped by SIGSTOP before attaching. */
+ int was_stopped;
+
/* Non-zero if this LWP will be/has been resumed. Note that an LWP
can be marked both as stopped and resumed at the same time. This
happens if we try to resume an LWP that has a wait status
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ ./gdb/testsuite/gdb.threads/attach-into-signal.c 29 Jun 2007 22:06:05 -0000
@@ -0,0 +1,70 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+ Copyright 2007 Free Software Foundation, Inc.
+
+ 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 2 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., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */
+
+#include <signal.h>
+#include <unistd.h>
+#include <string.h>
+#include <stdio.h>
+#include <stdlib.h>
+#ifdef USE_THREADS
+#include <pthread.h>
+#endif
+
+void action(int sig, siginfo_t * info, void *uc)
+{
+ raise (SIGALRM);
+}
+
+static void *func (void *arg)
+{
+ struct sigaction act;
+
+ memset (&act, 0, sizeof(struct sigaction));
+ act.sa_sigaction = action;
+ act.sa_flags = SA_RESTART;
+ sigaction (SIGALRM, &act, 0);
+
+ raise (SIGALRM);
+
+ /* It is an upstream kernel bug (2.6.22-rc4-git7.x86_64, PREEMPT, SMP).
+ We never get here without ptrace(2) but we get while under ptrace(2). */
+ for (;;)
+ pause ();
+
+ abort ();
+ /* NOTREACHED */
+ return NULL;
+}
+
+int main ()
+{
+
+#ifndef USE_THREADS
+
+ func (NULL);
+
+#else
+
+ pthread_t th;
+ pthread_create (&th, NULL, func, NULL);
+ pthread_join (th, NULL);
+
+#endif
+
+ return 0;
+}
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ ./gdb/testsuite/gdb.threads/attach-into-signal.exp 29 Jun 2007 22:06:06 -0000
@@ -0,0 +1,176 @@
+# Copyright 2007
+
+# 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 2 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., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+
+# This test was created by modifying attach-stopped.exp.
+# This file was created by Jan Kratochvil <jan.kratochvil@redhat.com>.
+
+if $tracelevel then {
+ strace $tracelevel
+}
+
+set prms_id 0
+set bug_id 0
+
+set testfile "attach-into-signal"
+set srcfile ${testfile}.c
+set binfile ${objdir}/${subdir}/${testfile}
+set escapedbinfile [string_to_regexp ${objdir}/${subdir}/${testfile}]
+
+remote_exec build "rm -f ${binfile}"
+# For debugging this test
+#
+#log_user 1
+
+proc corefunc { threadtype } {
+ global srcfile
+ global binfile
+ global escapedbinfile
+ global srcdir
+ global subdir
+ global gdb_prompt
+
+ if [get_compiler_info ${binfile}] {
+ return -1
+ }
+
+ # Start the program running and then wait for a bit, to be sure
+ # that it can be attached to.
+ # Statistically there is a better chance without giving process a nice.
+
+ set testpid [eval exec $binfile &]
+ exec sleep 2
+
+ # Run 2 passes of the test.
+ # The C file inferior stops pending its signals if a single one is lost,
+ # we test successful redelivery of the caught signal by the 2nd pass.
+
+ # linux-2.6.20.4.x86_64 had maximal attempt # 20 in 4 test runs.
+ set attempts 100
+ set attempt 1
+ set passes 1
+ while { $passes < 3 && $attempt <= $attempts } {
+
+ # Start with clean gdb
+ gdb_exit
+
+ set stoppedtry 0
+ while { $stoppedtry < 10 } {
+ set fileid [open /proc/${testpid}/status r];
+ gets $fileid line1;
+ gets $fileid line2;
+ close $fileid;
+
+ if {![string match "*(stopped)*" $line2]} {
+ # No PASS message as we may be looping in multiple attempts.
+ break
+ }
+ sleep 1
+ set stoppedtry [expr $stoppedtry + 1]
+ }
+ if { $stoppedtry >= 10 } {
+ verbose -log $line2
+ set test "$threadtype: process is still running on the attempt # $attempt of $attempts"
+ break
+ }
+
+ gdb_start
+ gdb_reinitialize_dir $srcdir/$subdir
+ gdb_load ${binfile}
+
+ # No PASS message as we may be looping in multiple attempts.
+ gdb_test "set debug lin-lwp 1" "" ""
+
+ set test "$threadtype: set file (pass $passes), before attach1 to stopped process"
+ if {[gdb_test_multiple "file $binfile" $test {
+ -re "Load new symbol table from.*y or n. $" {
+ # No PASS message as we may be looping in multiple attempts.
+ gdb_test "y" "Reading symbols from $escapedbinfile\.\.\.*done." ""
+ }
+ -re "Reading symbols from $escapedbinfile\.\.\.*done.*$gdb_prompt $" {
+ # No PASS message as we may be looping in multiple attempts.
+ }
+ }] != 0 } {
+ break
+ }
+
+ # Main test:
+ set test "$threadtype: attach (pass $passes), pending signal catch"
+ if {[gdb_test_multiple "attach $testpid" $test {
+ -re "Attaching to program.*`?$escapedbinfile'?, process $testpid.*Redelivering pending Alarm clock..*$gdb_prompt $" {
+ # nonthreaded:
+ pass $test
+ verbose -log "$test succeeded on the attempt # $attempt of $attempts"
+ set passes [expr $passes + 1]
+ }
+ -re "Attaching to program.*`?$escapedbinfile'?, process $testpid.*$gdb_prompt $" {
+ # nonthreaded:
+ # We just lack the luck, we should try it again.
+ set attempt [expr $attempt + 1]
+ }
+ -re "Attaching to process $testpid.*Redelivering pending Alarm clock..*$gdb_prompt $" {
+ # threaded:
+ pass $test
+ verbose -log "$test succeeded on the attempt # $attempt of $attempts"
+ set passes [expr $passes + 1]
+ }
+ -re "Attaching to process $testpid.*$gdb_prompt $" {
+ # threaded:
+ # We just lack the luck, we should try it again.
+ set attempt [expr $attempt - 1]
+ }
+ }] != 0 } {
+ break
+ }
+ }
+ if {$passes < 3} {
+ if {$attempt > $attempts} {
+ unresolved $test
+ } else {
+ fail $test
+ }
+ }
+
+ # Exit and detach the process.
+
+ gdb_exit
+
+ # Make sure we don't leave a process around to confuse
+ # the next test run (and prevent the compile by keeping
+ # the text file busy), in case the "set should_exit" didn't
+ # work.
+
+ # Continue the program - some Linux kernels need it before -9 if the
+ # process is stopped.
+ remote_exec build "kill -s CONT ${testpid}"
+
+ remote_exec build "kill -9 ${testpid}"
+}
+
+# build the test case first without threads
+#
+if { [gdb_compile "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable {debug}] != "" } {
+ gdb_suppress_entire_file "Testcase nonthraded compile failed, so all tests in this file will automatically fail."
+}
+
+corefunc nonthreaded
+
+# build the test case also with threads
+#
+if { [gdb_compile_pthreads "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable {debug additional_flags=-DUSE_THREADS}] != "" } {
+ gdb_suppress_entire_file "Testcase threaded compile failed, so all tests in this file will automatically fail."
+}
+
+corefunc threaded
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ ./gdb/testsuite/gdb.threads/attach-stopped.c 29 Jun 2007 22:06:06 -0000
@@ -0,0 +1,51 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+ Copyright 2005-2007 Free Software Foundation, Inc.
+
+ 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 2 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., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */
+
+/* This program is intended to be started outside of gdb, then
+ manually stopped via a signal. */
+
+#include <stddef.h>
+#include <unistd.h>
+#ifdef USE_THREADS
+#include <pthread.h>
+#endif
+
+static void *func (void *arg)
+{
+ sleep (10000); /* Ridiculous time, but we will eventually kill it. */
+ sleep (10000); /* Second sleep. */
+ return NULL;
+}
+
+int main ()
+{
+
+#ifndef USE_THREADS
+
+ func (NULL);
+
+#else
+
+ pthread_t th;
+ pthread_create (&th, NULL, func, NULL);
+ pthread_join (th, NULL);
+
+#endif
+
+ return 0;
+}
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ ./gdb/testsuite/gdb.threads/attach-stopped.exp 29 Jun 2007 22:06:06 -0000
@@ -0,0 +1,213 @@
+# Copyright 2005-2007
+
+# 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 2 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., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+
+# This test was created by modifying attach.exp.
+# This file was created by Jeff Johnston <jjohnstn@redhat.com>.
+# This file was updated by Jan Kratochvil <jan.kratochvil@redhat.com>.
+
+if $tracelevel then {
+ strace $tracelevel
+}
+
+set prms_id 0
+set bug_id 0
+
+# This test only works on Linux
+if { ![istarget "*-*-linux-gnu*"] } {
+ return 0
+}
+
+set testfile "attach-stopped"
+set srcfile ${testfile}.c
+set binfile ${objdir}/${subdir}/${testfile}
+set escapedbinfile [string_to_regexp ${objdir}/${subdir}/${testfile}]
+
+#execute_anywhere "rm -f ${binfile}"
+remote_exec build "rm -f ${binfile}"
+# For debugging this test
+#
+#log_user 1
+
+proc corefunc { threadtype } {
+ global srcfile
+ global binfile
+ global escapedbinfile
+ global srcdir
+ global subdir
+ global gdb_prompt
+
+ if [get_compiler_info ${binfile}] {
+ return -1
+ }
+
+ # Start the program running and then wait for a bit, to be sure
+ # that it can be attached to.
+
+ set testpid [eval exec $binfile &]
+
+ # Avoid some race:
+ sleep 2
+
+ # Stop the program
+ remote_exec build "kill -s STOP ${testpid}"
+
+ # Start with clean gdb
+ gdb_exit
+ gdb_start
+ gdb_reinitialize_dir $srcdir/$subdir
+ gdb_load ${binfile}
+
+ # Verify that we can attach to the process by first giving its
+ # executable name via the file command, and using attach with the
+ # process ID.
+
+ set test "$threadtype: set file, before attach1 to stopped process"
+ gdb_test_multiple "file $binfile" "$test" {
+ -re "Load new symbol table from.*y or n. $" {
+ gdb_test "y" "Reading symbols from $escapedbinfile\.\.\.*done." \
+ "$test (re-read)"
+ }
+ -re "Reading symbols from $escapedbinfile\.\.\.*done.*$gdb_prompt $" {
+ pass "$test"
+ }
+ }
+
+ set test "$threadtype: attach1 to stopped, after setting file"
+ gdb_test_multiple "attach $testpid" "$test" {
+ -re "Attaching to program.*`?$escapedbinfile'?, process $testpid.*$gdb_prompt $" {
+ pass "$test"
+ }
+ }
+
+ if {[string equal $threadtype threaded]} {
+ gdb_test "thread apply all bt" ".*sleep.*clone.*" "$threadtype: attach1 to stopped bt"
+ } else {
+ gdb_test "bt" ".*sleep.*main.*" "$threadtype: attach1 to stopped bt"
+ }
+
+ # Exit and detach the process.
+
+ gdb_exit
+
+ # Avoid some race:
+ sleep 2
+
+ set fileid [open /proc/${testpid}/status r];
+ gets $fileid line1;
+ gets $fileid line2;
+ close $fileid;
+
+ set test "$threadtype: attach1, exit leaves process stopped"
+ if {[string match "*(stopped)*" $line2]} {
+ pass $test
+ } else {
+ fail $test
+ }
+
+ # At this point, the process should still be stopped
+
+ gdb_start
+ gdb_reinitialize_dir $srcdir/$subdir
+ gdb_load ${binfile}
+
+ # Verify that we can attach to the process just by giving the
+ # process ID.
+
+ set test "$threadtype: attach2 to stopped, after setting file"
+ gdb_test_multiple "attach $testpid" "$test" {
+ -re "Attaching to program.*`?$escapedbinfile'?, process $testpid.*$gdb_prompt $" {
+ pass "$test"
+ }
+ }
+
+ if {[string equal $threadtype threaded]} {
+ gdb_test "thread apply all bt" ".*sleep.*clone.*" "$threadtype: attach2 to stopped bt"
+ } else {
+ gdb_test "bt" ".*sleep.*main.*" "$threadtype: attach2 to stopped bt"
+ }
+ gdb_breakpoint [gdb_get_line_number "$threadtype: Second sleep"]
+ set test "$threadtype: attach2 continue"
+ send_gdb "continue\n"
+ gdb_expect {
+ -re "Continuing"
+ { pass "continue ($test)" }
+ timeout
+ { fail "continue ($test) (timeout)" }
+ }
+
+ # For this to work we must be sure to consume the "Continuing."
+ # message first, or GDB's signal handler may not be in place.
+ after 1000 {send_gdb "\003"}
+ set test "$threadtype: attach2 stop interrupt"
+ gdb_expect 10 {
+ -re "Program received signal SIGINT.*$gdb_prompt $"
+ {
+ pass $test
+ }
+ -re "Breakpoint \[0-9\].*$srcfile.*$gdb_prompt $"
+ {
+ pass $test
+ }
+ timeout
+ {
+ fail $test
+ }
+ }
+
+ gdb_exit
+
+ # Avoid some race:
+ sleep 2
+
+ # At this point, the process should be sleeping
+
+ set fileid2 [open /proc/${testpid}/status r];
+ gets $fileid2 line1;
+ gets $fileid2 line2;
+ close $fileid2;
+
+ set test "$threadtype: attach2, exit leaves process sleeping"
+ if {[string match "*(sleeping)*" $line2]} {
+ pass $test
+ } else {
+ fail $test
+ }
+
+ # Make sure we don't leave a process around to confuse
+ # the next test run (and prevent the compile by keeping
+ # the text file busy), in case the "set should_exit" didn't
+ # work.
+
+ remote_exec build "kill -9 ${testpid}"
+}
+
+# build the test case first without threads
+#
+if { [gdb_compile "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable {debug}] != "" } {
+ gdb_suppress_entire_file "Testcase nonthraded compile failed, so all tests in this file will automatically fail."
+}
+
+corefunc nonthreaded
+
+# build the test case first without threads
+#
+if { [gdb_compile_pthreads "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable {debug additional_flags=-DUSE_THREADS}] != "" } {
+ gdb_suppress_entire_file "Testcase threaded compile failed, so all tests in this file will automatically fail."
+}
+
+corefunc threaded
+
+return 0
--- ./gdb/doc/gdb.texinfo 1 Jul 2007 09:13:05 -0000 1.418
+++ ./gdb/doc/gdb.texinfo 1 Jul 2007 09:55:14 -0000
@@ -2167,16 +2167,29 @@ can step and continue; you can modify st
process continue running, you may use the @code{continue} command after
attaching @value{GDBN} to the process.

+For a process already being stopped before the @code{attach} command executed
+you get the informational message below. Other signals may be occasionally
+shown if they were being delivered right the time the @code{attach} command
+executed. Such process is left still stopped after the @code{detach} command
+as long as you have not used the @code{continue} command (or similiar one)
+during your debugging session.
+
+@smallexample
+Attaching to program: /bin/sleep, process 16289
+Redelivering pending Stopped (signal).
+@end smallexample
+
@table @code
@kindex detach
@item detach
When you have finished debugging the attached process, you can use the
-@code{detach} command to release it from @value{GDBN} control. Detaching
-the process continues its execution. After the @code{detach} command,
-that process and @value{GDBN} become completely independent once more, and you
-are ready to @code{attach} another process or start one with @code{run}.
-@code{detach} does not repeat if you press @key{RET} again after
-executing the command.
+@code{detach} command to release it from @value{GDBN} control. Detaching the
+process continues its execution unless it was already stopped before the
+attachment and a @code{continue} type command has not been executed. After the
+@code{detach} command, that process and @value{GDBN} become completely
+independent once more, and you are ready to @code{attach} another process or
+start one with @code{run}. @code{detach} does not repeat if you press
+@key{RET} again after executing the command.
@end table

If you exit @value{GDBN} while you have an attached process, you detach