[PATCH/7.11.1?] Simpler fix PR gdb/19828: gdb -p <process from a container>: internal error

[PATCH/7.11.1?] Simpler fix PR gdb/19828: gdb -p <process from a container>: internal error

[Pedro Alves]

(PR gdb/19828 is marked as a 7.11.1 blocker.)

So this is the simpler version of patch #6 included in this series:

  https://sourceware.org/ml/gdb-patches/2016-05/msg00328.html

This is the version of the patch that Fedora has been carrying for a
few weeks.  It's sufficient to fix the use case reported in PR
gdb/19828.

However, while working on the test for the fix, I had the bright idea
of making it try "attach&" as well as "attach", and then that exposed
that the fix was incomplete (gdb hits internal errors).

And then I wrote the complete fix, but that in turn exposed the need
for the rest of optimization work in the series linked above...

Probably safer to include this one in 7.11.1 instead of the larger
series, though it does leave "attach&" broken...  In any case,
probably better to let the other series soak a bit on master before
backporting, which suggests pushing this simpler version first anyway?

Comments?

Pedro Alves (1):
  Fix PR gdb/19828: gdb -p <process from a container>: internal error

 gdb/linux-nat.c                                   |  5 ++
 gdb/testsuite/gdb.threads/clone-attach-detach.c   | 66 +++++++++++++++++++++++
 gdb/testsuite/gdb.threads/clone-attach-detach.exp | 63 ++++++++++++++++++++++
 3 files changed, 134 insertions(+)
 create mode 100644 gdb/testsuite/gdb.threads/clone-attach-detach.c
 create mode 100644 gdb/testsuite/gdb.threads/clone-attach-detach.exp

-- 
2.5.5

[PATCH] Fix PR gdb/19828: gdb -p <process from a container>: internal error

[Pedro Alves]

When GDB attaches to a process, it looks at the /proc/PID/task/ dir
for all clone threads of that process, and attaches to each of them.

Usually, if there is more than one clone thread, it means the program
is multi threaded and linked with pthreads.  Thus when GDB soon after
attaching finds and loads a libthread_db matching the process, it'll
add a thread to the thread list for each of the initially found
lower-level LWPs.

If, however, GDB fails to find/load a matching libthread_db, nothing
is adding the LWPs to the thread list.  And because of that, "detach"
hits an internal error:

  (gdb) PASS: gdb.threads/clone-attach-detach.exp: fg attach 1: attach
  info threads
    Id   Target Id         Frame
  * 1    LWP 6891 "clone-attach-de" 0x00007f87e5fd0790 in __nanosleep_nocancel () at ../sysdeps/unix/syscall-template.S:84
  (gdb) FAIL: gdb.threads/clone-attach-detach.exp: fg attach 1: info threads shows two LWPs
  detach
  .../src/gdb/thread.c:1010: internal-error: is_executing: Assertion `tp' failed.
  A problem internal to GDB has been detected,
  further debugging may prove unreliable.
  Quit this debugging session? (y or n)
  FAIL: gdb.threads/clone-attach-detach.exp: fg attach 1: detach (GDB internal error)

From here:

  ...
  #8  0x00000000007ba7cc in internal_error (file=0x98ea68 ".../src/gdb/thread.c", line=1010, fmt=0x98ea30 "%s: Assertion `%s' failed.")
      at .../src/gdb/common/errors.c:55
  #9  0x000000000064bb83 in is_executing (ptid=...) at .../src/gdb/thread.c:1010
  #10 0x00000000004c23bb in get_pending_status (lp=0x12c5cc0, status=0x7fffffffdc0c) at .../src/gdb/linux-nat.c:1235
  #11 0x00000000004c2738 in detach_callback (lp=0x12c5cc0, data=0x0) at .../src/gdb/linux-nat.c:1317
  #12 0x00000000004c1a2a in iterate_over_lwps (filter=..., callback=0x4c2599 <detach_callback>, data=0x0) at .../src/gdb/linux-nat.c:899
  #13 0x00000000004c295c in linux_nat_detach (ops=0xe7bd30, args=0x0, from_tty=1) at .../src/gdb/linux-nat.c:1358
  #14 0x000000000068284d in delegate_detach (self=0xe7bd30, arg1=0x0, arg2=1) at .../src/gdb/target-delegates.c:34
  #15 0x0000000000694141 in target_detach (args=0x0, from_tty=1) at .../src/gdb/target.c:2241
  #16 0x0000000000630582 in detach_command (args=0x0, from_tty=1) at .../src/gdb/infcmd.c:2975
  ...

Tested on x86-64 Fedora 23.  Also confirmed the test passes against
gdbserver with with "maint set target-non-stop".

gdb/ChangeLog:
yyyy-mm-dd  Pedro Alves  <palves@redhat.com>

	* linux-nat.c (attach_proc_task_lwp_callback): Add the thread to
	GDB's thread list.

testsuite/ChangeLog:
yyyy-mm-dd  Pedro Alves  <palves@redhat.com>

	* gdb.threads/clone-attach-detach.c: New file.
	* gdb.threads/clone-attach-detach.exp: New file.
---
 gdb/linux-nat.c                                   |  5 ++
 gdb/testsuite/gdb.threads/clone-attach-detach.c   | 66 +++++++++++++++++++++++
 gdb/testsuite/gdb.threads/clone-attach-detach.exp | 63 ++++++++++++++++++++++
 3 files changed, 134 insertions(+)
 create mode 100644 gdb/testsuite/gdb.threads/clone-attach-detach.c
 create mode 100644 gdb/testsuite/gdb.threads/clone-attach-detach.exp

diff --git a/gdb/linux-nat.c b/gdb/linux-nat.c
index edde88d..383c722 100644
--- a/gdb/linux-nat.c
+++ b/gdb/linux-nat.c
@@ -1088,6 +1088,11 @@ attach_proc_task_lwp_callback (ptid_t ptid)
 	  /* 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;
+
+	  /* Also add the LWP to gdb's thread list, in case a
+	     matching libthread_db is not found (or the process uses
+	     raw clone).  */
+	  add_thread (lp->ptid);
 	}
 
       return 1;
diff --git a/gdb/testsuite/gdb.threads/clone-attach-detach.c b/gdb/testsuite/gdb.threads/clone-attach-detach.c
new file mode 100644
index 0000000..daa8f1f
--- /dev/null
+++ b/gdb/testsuite/gdb.threads/clone-attach-detach.c
@@ -0,0 +1,66 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2016 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 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/>.
+*/
+
+#define _GNU_SOURCE
+#include <sched.h>
+#include <assert.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#define STACK_SIZE 0x1000
+
+int clone_pid;
+
+static int
+clone_fn (void *unused)
+{
+  /* Wait for alarm.  */
+  while (1)
+    sleep (1);
+  return 0;
+}
+
+int
+main (int argc, char **argv)
+{
+  unsigned char *stack;
+  int res;
+
+  alarm (300);
+
+  stack = malloc (STACK_SIZE);
+  assert (stack != NULL);
+
+#define CLONE_FLAGS (CLONE_THREAD | CLONE_SIGHAND | CLONE_VM)
+
+#ifdef __ia64__
+  clone_pid = __clone2 (clone_fn, stack, STACK_SIZE, CLONE_FLAGS, NULL);
+#else
+  clone_pid = clone (clone_fn, stack + STACK_SIZE, CLONE_FLAGS, NULL);
+#endif
+
+  assert (clone_pid > 0);
+
+  /* Wait for alarm.  */
+  while (1)
+    sleep (1);
+
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.threads/clone-attach-detach.exp b/gdb/testsuite/gdb.threads/clone-attach-detach.exp
new file mode 100644
index 0000000..0652108
--- /dev/null
+++ b/gdb/testsuite/gdb.threads/clone-attach-detach.exp
@@ -0,0 +1,63 @@
+# This testcase is part of GDB, the GNU debugger.
+
+# Copyright 2016 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 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/>.
+
+# Test attach / detach from a process that uses raw clone.  We use raw
+# clone as proxy for when libthread_db is not available.
+
+# This only works on targets with the Linux kernel.
+if ![istarget *-*-linux*] {
+    return
+}
+
+if {![can_spawn_for_attach]} {
+    return 0
+}
+
+standard_testfile
+
+if [prepare_for_testing "failed to prepare" $testfile $srcfile {debug}] {
+    return -1
+}
+
+clean_restart ${binfile}
+
+set test_spawn_id [spawn_wait_for_attach $binfile]
+set testpid [spawn_id_get_pid $test_spawn_id]
+
+# Native/gdbserver.
+set thread_re "(LWP $decimal|Thread )"
+
+# Try attach / detach a few times, in case GDB ends up with stale
+# state after detaching.
+
+set attempts 3
+for {set attempt 1} {$attempt <= $attempts} {incr attempt} {
+    with_test_prefix "fg attach $attempt" {
+
+	gdb_test "attach $testpid" \
+	    "Attaching to program.*process $testpid.*" \
+	    "attach"
+
+	gdb_test "info threads" \
+	    "1.*${thread_re}.*\r\n.*2.*${thread_re}.*" \
+	    "info threads shows two LWPs"
+
+	gdb_test "detach" "Detaching from .*, process $testpid"
+    }
+}
+
+kill_wait_spawned_process $test_spawn_id
-- 
2.5.5