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Re: [RFA/Linux] Ask kernel to kill inferior when GDB terminates
- From: Joel Brobecker <brobecker at adacore dot com>
- To: Pedro Alves <palves at redhat dot com>
- Cc: gdb-patches at sourceware dot org
- Date: Mon, 15 Dec 2014 19:39:35 -0500
- Subject: Re: [RFA/Linux] Ask kernel to kill inferior when GDB terminates
- Authentication-results: sourceware.org; auth=none
- References: <1415984034-27122-1-git-send-email-brobecker at adacore dot com> <54663729 dot 6010708 at redhat dot com> <20141114173255 dot GD5774 at adacore dot com> <20141119092547 dot GP5774 at adacore dot com> <546C69D4 dot 5090300 at redhat dot com> <20141213162757 dot GL5457 at adacore dot com> <548EE088 dot 20506 at redhat dot com> <20141215204323 dot GE5457 at adacore dot com> <548F4FFC dot 8060509 at redhat dot com>
> This makes it sound like "interruptible sleep" is some kind of wedged
> state waiting for a debugger. But, this simply means your process is just
> running as normal, and your test's case, normal means idling. Most likely,
> your test program had a "sleep" call in it. IOW, it'd be in sleep state
> even if had been started outside gdb. Another test program could go
> to "T (stopped)", "R (running)", etc.
You're right. Rev log updated.
> This test must be called unconditionally. current_ptrace_options is
> only initialized once:
>
> void
> linux_enable_event_reporting (pid_t pid)
> {
> /* Check if we have initialized the ptrace features for this
> target. If not, do it now. */
> if (current_ptrace_options == -1)
> linux_check_ptrace_features ();
>
> so if the first process gdbserver debugs is an "attach" process,
> but the second one is not, you'll miss setting PTRACE_O_EXITKILL on
> the second process.
>
> Instead, always call linux_test_for_exitkill, and then in
> linux_enable_event_reporting mask out PTRACE_O_EXITKILL
> from current_ptrace_options if 'attached' is false.
Right again.
Here is an attached patch. Re-tested on x86_64-linux as previously
done.
gdb/ChangeLog:
* nat/linux-ptrace.h (PTRACE_O_EXITKILL): Define if not
already defined.
(linux_enable_event_reporting): Add parameter "attached".
* nat/linux-ptrace.c (linux_test_for_exitkill): New advance
declaration. New function.
(linux_check_ptrace_features): Add linux_test_for_exitkill call.
(linux_enable_event_reporting): Add new parameter "attached".
Do not call ptrace with the PTRACE_O_EXITKILL if ATTACHED is
nonzero.
* linux-nat.c (linux_init_ptrace): Add parameter "attached".
Use it. Update function description.
(linux_child_post_attach, linux_child_post_startup_inferior):
Update call to linux_enable_event_reporting.
gdb/gdbserver/ChangeLog:
* linux-low.c (linux_low_filter_event): Update call to
linux_enable_event_reporting following the addition of
a new parameter to that function.
Thanks, Pedro.
--
Joel
>From 4ad92cbfc3dfdfffe46f20e2b6e8df7a793c9ea7 Mon Sep 17 00:00:00 2001
From: Joel Brobecker <brobecker@adacore.com>
Date: Tue, 11 Nov 2014 10:07:21 +0400
Subject: [PATCH] [Linux] Ask kernel to kill inferior when GDB terminates
This patch enhances GDB on GNU/Linux systems in the situation where
we are debugging an inferior that was created from GDB (as opposed
to attached to), by asking the kernel to kill the inferior if GDB
terminates without doing it itself.
This would typically happen when GDB encounters a problem and
crashes, or when it gets killed by an external process. This can
be observed by starting a program under GDB, and then killing
GDB with signal 9. After GDB is killed, the inferior still remains.
This patch also fixes GDBserver similarly.
This fix is conditional on the kernel supporting the PTRACE_O_EXITKILL
feature. On older kernels, the behavior remains unchanged.
gdb/ChangeLog:
* nat/linux-ptrace.h (PTRACE_O_EXITKILL): Define if not
already defined.
(linux_enable_event_reporting): Add parameter "attached".
* nat/linux-ptrace.c (linux_test_for_exitkill): New advance
declaration. New function.
(linux_check_ptrace_features): Add linux_test_for_exitkill call.
(linux_enable_event_reporting): Add new parameter "attached".
Do not call ptrace with the PTRACE_O_EXITKILL if ATTACHED is
nonzero.
* linux-nat.c (linux_init_ptrace): Add parameter "attached".
Use it. Update function description.
(linux_child_post_attach, linux_child_post_startup_inferior):
Update call to linux_enable_event_reporting.
gdb/gdbserver/ChangeLog:
* linux-low.c (linux_low_filter_event): Update call to
linux_enable_event_reporting following the addition of
a new parameter to that function.
Tested on x86_64-linux, native and native-gdbserver.
I also verified by hand that the inferior gets killed when killing
GDB in the "run" case, while the inferior remains in the "attach"
case. Same for GDBserver.
---
gdb/gdbserver/linux-low.c | 4 +++-
gdb/linux-nat.c | 12 +++++++-----
gdb/nat/linux-ptrace.c | 34 +++++++++++++++++++++++++++++++---
gdb/nat/linux-ptrace.h | 7 ++++++-
4 files changed, 47 insertions(+), 10 deletions(-)
diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
index 5ea9200..65f72a2 100644
--- a/gdb/gdbserver/linux-low.c
+++ b/gdb/gdbserver/linux-low.c
@@ -1878,7 +1878,9 @@ linux_low_filter_event (ptid_t filter_ptid, int lwpid, int wstat)
if (WIFSTOPPED (wstat) && child->must_set_ptrace_flags)
{
- linux_enable_event_reporting (lwpid);
+ struct process_info *proc = find_process_pid (pid_of (thread));
+
+ linux_enable_event_reporting (lwpid, proc->attached);
child->must_set_ptrace_flags = 0;
}
diff --git a/gdb/linux-nat.c b/gdb/linux-nat.c
index 29133f9..845d566 100644
--- a/gdb/linux-nat.c
+++ b/gdb/linux-nat.c
@@ -321,25 +321,27 @@ pull_pid_from_list (struct simple_pid_list **listp, int pid, int *statusp)
}
/* Initialize ptrace warnings and check for supported ptrace
- features given PID. */
+ features given PID.
+
+ ATTACHED should be nonzero iff we attached to the inferior. */
static void
-linux_init_ptrace (pid_t pid)
+linux_init_ptrace (pid_t pid, int attached)
{
- linux_enable_event_reporting (pid);
+ linux_enable_event_reporting (pid, attached);
linux_ptrace_init_warnings ();
}
static void
linux_child_post_attach (struct target_ops *self, int pid)
{
- linux_init_ptrace (pid);
+ linux_init_ptrace (pid, 1);
}
static void
linux_child_post_startup_inferior (struct target_ops *self, ptid_t ptid)
{
- linux_init_ptrace (ptid_get_pid (ptid));
+ linux_init_ptrace (ptid_get_pid (ptid), 0);
}
/* Return the number of known LWPs in the tgid given by PID. */
diff --git a/gdb/nat/linux-ptrace.c b/gdb/nat/linux-ptrace.c
index 8bc3f16..a0e0c32 100644
--- a/gdb/nat/linux-ptrace.c
+++ b/gdb/nat/linux-ptrace.c
@@ -307,6 +307,7 @@ linux_child_function (gdb_byte *child_stack)
static void linux_test_for_tracesysgood (int child_pid);
static void linux_test_for_tracefork (int child_pid);
+static void linux_test_for_exitkill (int child_pid);
/* Determine ptrace features available on this target. */
@@ -338,6 +339,8 @@ linux_check_ptrace_features (void)
linux_test_for_tracefork (child_pid);
+ linux_test_for_exitkill (child_pid);
+
/* Clean things up and kill any pending children. */
do
{
@@ -449,19 +452,44 @@ linux_test_for_tracefork (int child_pid)
"(%d, status 0x%x)"), ret, status);
}
-/* Enable reporting of all currently supported ptrace events. */
+/* Determine if PTRACE_O_EXITKILL can be used. */
+
+static void
+linux_test_for_exitkill (int child_pid)
+{
+ int ret;
+
+ ret = ptrace (PTRACE_SETOPTIONS, child_pid, (PTRACE_TYPE_ARG3) 0,
+ (PTRACE_TYPE_ARG4) PTRACE_O_EXITKILL);
+
+ if (ret == 0)
+ current_ptrace_options |= PTRACE_O_EXITKILL;
+}
+
+/* Enable reporting of all currently supported ptrace events.
+ ATTACHED should be nonzero if we have attached to the inferior. */
void
-linux_enable_event_reporting (pid_t pid)
+linux_enable_event_reporting (pid_t pid, int attached)
{
+ int ptrace_options;
+
/* Check if we have initialized the ptrace features for this
target. If not, do it now. */
if (current_ptrace_options == -1)
linux_check_ptrace_features ();
+ ptrace_options = current_ptrace_options;
+ if (attached)
+ {
+ /* When attached to our inferior, we do not want the inferior
+ to die with us if we terminate unexpectedly. */
+ ptrace_options &= ~PTRACE_O_EXITKILL;
+ }
+
/* Set the options. */
ptrace (PTRACE_SETOPTIONS, pid, (PTRACE_TYPE_ARG3) 0,
- (PTRACE_TYPE_ARG4) (uintptr_t) current_ptrace_options);
+ (PTRACE_TYPE_ARG4) (uintptr_t) ptrace_options);
}
/* Disable reporting of all currently supported ptrace events. */
diff --git a/gdb/nat/linux-ptrace.h b/gdb/nat/linux-ptrace.h
index 31a77cd..588d38a 100644
--- a/gdb/nat/linux-ptrace.h
+++ b/gdb/nat/linux-ptrace.h
@@ -69,6 +69,11 @@ struct buffer;
#endif /* PTRACE_EVENT_FORK */
+#ifndef PTRACE_O_EXITKILL
+/* Only defined in Linux Kernel 3.8 or later. */
+#define PTRACE_O_EXITKILL 0x00100000
+#endif
+
#if (defined __bfin__ || defined __frv__ || defined __sh__) \
&& !defined PTRACE_GETFDPIC
#define PTRACE_GETFDPIC 31
@@ -85,7 +90,7 @@ struct buffer;
extern void linux_ptrace_attach_fail_reason (pid_t pid, struct buffer *buffer);
extern void linux_ptrace_init_warnings (void);
-extern void linux_enable_event_reporting (pid_t pid);
+extern void linux_enable_event_reporting (pid_t pid, int attached);
extern void linux_disable_event_reporting (pid_t pid);
extern int linux_supports_tracefork (void);
extern int linux_supports_traceclone (void);
--
1.9.1