[PATCH 08/10] Extended-remote follow vfork

Don Breazeal
2014-08-07T18:01:01Z

This patch implements follow-fork for vfork on extended-remote linux targets.

The implementation follows the native implementation as much as possible. Most of the work is done on the GDB side in the existing code now in infrun.c. GDBserver just has to report the events and do a little bookkeeping.

Implementation was almost entirely in gdbserver, excepting changes to gdb/remote.c, and included:

* enabling VFORK events
- by adding ptrace options for VFORK and VFORK_DONE as 'additional options' in linux-low.c:initialize_low, so that they are available for extended-mode.

- by adding ptrace options for VFORK and VFORK_DONE as 'base options' in linux-low.c:linux_enable_extended_features. In this function we know we are in extended-mode, so we enable these options if they are supported.

* handling VFORK and VFORK_DONE events in linux-low.c:handle_extended_wait by saving the event information for event reporting and for the follow_fork request expected to come from GDB.

* handling VFORK in linux-low.c:linux_follow_fork, for the case where VFORK_DONE is supported and the case where it is not. This code is very similar to the code in linux-nat.c:linux_child_follow_fork, but slight differences in the data structures between the two implementations led me to keep them separate.

* include VFORK and VFORK_DONE events in the predicate linux-low.c:extended_event_reported.

* add support for VFORK and VFORK_DONE events in RSP by adding stop reasons "vfork" and "vforkdone" to the 'T' Stop Reply Packet in both gdbserver/remote-utils.c and gdb/remote.c.

Tested on x64 Ubuntu Lucid, native, remote, extended-remote. Also tested (on the same system) support for systems lacking VFORK_DONE events by modifying gdbserver to simulate that case.

Thanks,
--Don

gdb/
2014-08-06 Don Breazeal <donb@codesourcery.com>
* remote.c: New stop reasons "vfork"
and "vforkdone" for RSP 'T' Stop Reply Packet.

gdb/gdbserver/
2014-08-06 Don Breazeal <donb@codesourcery.com>
* linux-low.c (handle_extended_wait): Handle PTRACE_EVENT_VFORK and
PTRACE_EVENT_VFORK_DONE.
(linux_enable_extended_features): Enable PTRACE_EVENT_VFORK and
PTRACE_EVENT_VFORK_DONE.
(linux_follow_fork): Handle following a vfork.
(extended_event_reported): Add vfork and vfork-done events to
the list of extended events.
(initialize_low): Enable PTRACE_EVENT_VFORK and
PTRACE_EVENT_VFORK_DONE.
* remote-utils.c (prepare_resume_reply): New stop reasons "vfork"
and "vforkdone" for RSP 'T' Stop Reply Packet.

---
gdb/gdbserver/linux-low.c | 107 ++++++++++++++++++++++++++++++++++++------
gdb/gdbserver/remote-utils.c | 16 ++++++-
gdb/remote.c | 15 ++++++
3 files changed, 121 insertions(+), 17 deletions(-)

diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
index 4958fdb..69cad15 100644
--- a/gdb/gdbserver/linux-low.c
+++ b/gdb/gdbserver/linux-low.c
@@ -210,6 +210,7 @@ int using_threads = 1;
jump pads). */
static int stabilizing_threads;

+static void async_file_mark (void);
static void linux_resume_one_lwp (struct lwp_info *lwp,
int step, int signal, siginfo_t *info);
static void linux_resume (struct thread_resume *resume_info, size_t n);
@@ -218,6 +219,9 @@ static void unstop_all_lwps (int unsuspend, struct lwp_info *except);
static int linux_wait_for_event_filtered (ptid_t wait_ptid, ptid_t filter_ptid,
int *wstat, int options);
static int linux_wait_for_event (ptid_t ptid, int *wstat, int options);
+static ptid_t linux_wait_1 (ptid_t ptid,
+ struct target_waitstatus *ourstatus,
+ int target_options);
static struct lwp_info *add_lwp (ptid_t ptid);
static int linux_stopped_by_watchpoint (void);
static void mark_lwp_dead (struct lwp_info *lwp, int wstat);
@@ -379,7 +383,8 @@ handle_extended_wait (struct lwp_info *event_child, int wstat)
struct thread_info *event_thr = get_lwp_thread (event_child);
struct lwp_info *new_lwp;

- if (event == PTRACE_EVENT_FORK || event == PTRACE_EVENT_CLONE)
+ if (event == PTRACE_EVENT_FORK || event == PTRACE_EVENT_VFORK
+ || event == PTRACE_EVENT_CLONE)
{
ptid_t ptid;
unsigned long new_pid;
@@ -404,7 +409,7 @@ handle_extended_wait (struct lwp_info *event_child, int wstat)
warning ("wait returned unexpected status 0x%x", status);
}

- if (event == PTRACE_EVENT_FORK)
+ if (event == PTRACE_EVENT_FORK || event == PTRACE_EVENT_VFORK)
{
struct process_info *parent_proc;
struct process_info *child_proc;
@@ -444,12 +449,18 @@ handle_extended_wait (struct lwp_info *event_child, int wstat)
if (the_low_target.new_fork != NULL)
the_low_target.new_fork (parent_proc, child_proc);

- /* Save fork info for target processing. */
- current_inferior->pending_follow.kind = TARGET_WAITKIND_FORKED;
+ /* Save fork info for target processing and reporting to GDB. */
+ if (event == PTRACE_EVENT_FORK)
+ {
+ current_inferior->pending_follow.kind = TARGET_WAITKIND_FORKED;
+ event_child->waitstatus.kind = TARGET_WAITKIND_FORKED;
+ }
+ else if (event == PTRACE_EVENT_VFORK)
+ {
+ current_inferior->pending_follow.kind = TARGET_WAITKIND_VFORKED;
+ event_child->waitstatus.kind = TARGET_WAITKIND_VFORKED;
+ }
current_inferior->pending_follow.value.related_pid = ptid;
-
- /* Save fork info for reporting to GDB. */
- event_child->waitstatus.kind = TARGET_WAITKIND_FORKED;
event_child->waitstatus.value.related_pid = ptid;

/* Report the event. */
@@ -509,6 +520,11 @@ handle_extended_wait (struct lwp_info *event_child, int wstat)
/* Don't report the event. */
return 1;
}
+ else if (event == PTRACE_EVENT_VFORK_DONE)
+ {
+ event_child->waitstatus.kind = TARGET_WAITKIND_VFORK_DONE;
+ return 0;
+ }

internal_error (__FILE__, __LINE__, _("unknown ptrace event %d"), event);
}
@@ -1250,7 +1266,9 @@ linux_enable_extended_features (void)
/* There is no process yet, so include extended options in the
base options for subsequent ptrace configuration. */
linux_ptrace_set_desired_options (PTRACE_O_TRACECLONE
- | PTRACE_O_TRACEFORK, 0);
+ | PTRACE_O_TRACEFORK
+ | PTRACE_O_TRACEVFORK
+ | PTRACE_O_TRACEVFORKDONE, 0);
}
else
{
@@ -1298,6 +1316,7 @@ linux_follow_fork (int follow_child, int detach_fork)
{
struct inferior_list_entry *parent_inf;
struct thread_info *parent_thread;
+ int has_vforked;

parent_inf = find_inferior (&all_threads, is_parent_callback, NULL);

@@ -1307,7 +1326,8 @@ linux_follow_fork (int follow_child, int detach_fork)
return 0;

parent_thread = (struct thread_info *)parent_inf;
- parent_thread->pending_follow.kind = TARGET_WAITKIND_IGNORE;
+ has_vforked = (parent_thread->pending_follow.kind
+ == TARGET_WAITKIND_VFORKED);

if (!follow_child)
{
@@ -1350,7 +1370,7 @@ linux_follow_fork (int follow_child, int detach_fork)
signo = 0;

ptrace (PTRACE_DETACH, child_pid, 0, signo);
-
+
/* Deallocate all process-related storage. */
child_proc = find_process_pid (child_pid);
if (child_proc != NULL)
@@ -1359,8 +1379,63 @@ linux_follow_fork (int follow_child, int detach_fork)
current_inferior = NULL;
}
}
+
+ if (has_vforked)
+ {
+ struct lwp_info *parent_lp;
+
+ parent_lp = get_thread_lwp (parent_thread);
+ gdb_assert (linux_supports_tracefork () >= 0);
+
+ if (linux_supports_tracevforkdone ())
+ {
+ if (debug_threads)
+ {
+ debug_printf ("LFF: waiting for VFORK_DONE on %d\n",
+ ptid_get_pid (parent_thread->entry.id));
+ }
+ parent_lp->stopped = 1;
+
+ /* We'll handle the VFORK_DONE event like any other
+ event, in target_wait. */
+ }
+ else
+ {
+ /* We can't insert breakpoints until the child has
+ finished with the shared memory region. Without
+ VFORK_DONE events, the best we can do is to make sure it
+ runs for a little while. Hopefully it will be out of
+ range of any breakpoints we reinsert. Usually this
+ is only the single-step breakpoint at vfork's return
+ point.
+
+ See linux-nat.c:linux_child_follow_vfork for a more
+ detailed discussion of this. */
+
+ if (debug_threads)
+ debug_printf ("LFF: no VFORK_DONE support, sleeping a bit\n");
+
+ usleep (10000);
+
+ /* Pretend we've seen a PTRACE_EVENT_VFORK_DONE event,
+ and leave it pending. The next linux_resume_one_lwp call
+ will notice a pending event, and bypasses actually
+ resuming the inferior. */
+ parent_lp->status_pending_p = 1;
+ parent_lp->waitstatus.kind = TARGET_WAITKIND_VFORK_DONE;
+ parent_lp->stopped = 1;
+
+ /* If we're in async mode, need to tell the event loop
+ there's something here to process. */
+ if (target_is_async_p ())
+ async_file_mark ();
+ }
+ }
}

+ parent_thread->pending_follow.kind = TARGET_WAITKIND_IGNORE;
+ parent_thread->pending_follow.value.related_pid = null_ptid;
+
return 0;
}

@@ -2560,9 +2635,6 @@ static void move_out_of_jump_pad_callback (struct inferior_list_entry *entry);
static int stuck_in_jump_pad_callback (struct inferior_list_entry *entry,
void *data);
static int lwp_running (struct inferior_list_entry *entry, void *data);
-static ptid_t linux_wait_1 (ptid_t ptid,
- struct target_waitstatus *ourstatus,
- int target_options);

/* Stabilize threads (move out of jump pads).

@@ -2675,7 +2747,9 @@ extended_event_reported (const struct target_waitstatus *waitstatus)
if (waitstatus == NULL)
return 0;

- return (waitstatus->kind == TARGET_WAITKIND_FORKED);
+ return (waitstatus->kind == TARGET_WAITKIND_FORKED
+ || waitstatus->kind == TARGET_WAITKIND_VFORKED
+ || waitstatus->kind == TARGET_WAITKIND_VFORK_DONE);
}

/* Wait for process, returns status. */
@@ -6358,5 +6432,8 @@ initialize_low (void)

initialize_low_arch ();

- linux_ptrace_set_desired_options (PTRACE_O_TRACECLONE, PTRACE_O_TRACEFORK);
+ linux_ptrace_set_desired_options (PTRACE_O_TRACECLONE,
+ PTRACE_O_TRACEFORK
+ | PTRACE_O_TRACEVFORK
+ | PTRACE_O_TRACEVFORKDONE);
}
diff --git a/gdb/gdbserver/remote-utils.c b/gdb/gdbserver/remote-utils.c
index a3b12dd..00df57c 100644
--- a/gdb/gdbserver/remote-utils.c
+++ b/gdb/gdbserver/remote-utils.c
@@ -1112,15 +1112,18 @@ prepare_resume_reply (char *buf, ptid_t ptid,
{
case TARGET_WAITKIND_STOPPED:
case TARGET_WAITKIND_FORKED:
+ case TARGET_WAITKIND_VFORKED:
{
struct thread_info *saved_inferior;
const char **regp;
struct regcache *regcache;

- if (status->kind == TARGET_WAITKIND_FORKED && multi_process)
+ if ((status->kind == TARGET_WAITKIND_FORKED
+ || status->kind == TARGET_WAITKIND_VFORKED) && multi_process)
{
enum gdb_signal signal = GDB_SIGNAL_TRAP;
- const char *event = "fork";
+ const char *event = (status->kind == TARGET_WAITKIND_FORKED
+ ?"fork":"vfork");

sprintf (buf, "T%02x%s:p%x.%lx;", signal, event,
ptid_get_pid (status->value.related_pid),
@@ -1231,6 +1234,15 @@ prepare_resume_reply (char *buf, ptid_t ptid,
else
sprintf (buf, "X%02x", status->value.sig);
break;
+ case TARGET_WAITKIND_VFORK_DONE:
+ if (multi_process)
+ {
+ enum gdb_signal signal = GDB_SIGNAL_TRAP;
+ const char *event = "vforkdone";
+
+ sprintf (buf, "T%02x%s:;", signal, event);
+ }
+ break;
default:
error ("unhandled waitkind");
break;
diff --git a/gdb/remote.c b/gdb/remote.c
index d9989db..1304949 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -5510,6 +5510,21 @@ Packet: '%s'\n"),
event->ws.value.related_pid = read_ptid (++p1, &p);
event->ws.kind = TARGET_WAITKIND_FORKED;
}
+ else if (strncmp (p, "vfork", p1 - p) == 0)
+ {
+ event->ws.value.related_pid = read_ptid (++p1, &p);
+ event->ws.kind = TARGET_WAITKIND_VFORKED;
+ }
+ else if (strncmp (p, "vforkdone", p1 - p) == 0)
+ {
+ p1++;
+ p_temp = p1;
+ while (*p_temp && *p_temp != ';')
+ p_temp++;
+
+ event->ws.kind = TARGET_WAITKIND_VFORK_DONE;
+ p = p_temp;
+ }
else
{
/* Silently skip unknown optional info. */
--
1.7.0.4