obsd-nat: Various fixes for fork following.

- Don't use #ifdef's on ptrace ops.  obsd-nat.h didn't include
  <sys/ptrace.h>, so the virtual methods weren't always overridden
  causing the fork following to not work.  In addition, the thread and
  fork code is intertwined in ::wait and and the lack of #ifdef's
  there already assumed both were present.  Finally, both of these
  ptrace ops have been present in OpenBSD for at least 10 years.

- Move duplicated code to enable PTRACE_FORK event reporting to a
  single function and invoke it on new child processes reported via
  PTRACE_FORK.

- Don't return early from PTRACE_FORK handling, but instead reset
  wptid to the correct ptid if the child reports its event before the
  parent.  This allows the ptid fixup code to add thread IDs if the
  first event for a process is a PTRACE_FORK event.  This also
  properly returns ptid's with thread IDs when reporting PTRACE_FORK
  events.

- Handle detach_fork by skipping the PT_DETACH.

2 files changed, 25 insertions, 30 deletions

diff --git a/gdb/obsd-nat.c b/gdb/obsd-nat.c
index e7a7fb3..854fc9c 100644
--- a/gdb/obsd-nat.c
+++ b/gdb/obsd-nat.c
@@ -33,8 +33,6 @@
    that maps userland threads directly onto kernel threads in a 1:1
    fashion.  */
 
-#ifdef PT_GET_THREAD_FIRST
-
 std::string
 obsd_nat_target::pid_to_str (ptid_t ptid)
 {
@@ -72,6 +70,21 @@ obsd_nat_target::update_thread_list ()
     }
 }
 
+/* Enable additional event reporting on a new or existing process.  */
+
+static void
+obsd_enable_proc_events (pid_t pid)
+{
+  ptrace_event_t pe;
+
+  /* Set the initial event mask.  */
+  memset (&pe, 0, sizeof pe);
+  pe.pe_set_event |= PTRACE_FORK;
+  if (ptrace (PT_SET_EVENT_MASK, pid,
+	      (PTRACE_TYPE_ARG3)&pe, sizeof pe) == -1)
+    perror_with_name (("ptrace"));
+}
+
 ptid_t
 obsd_nat_target::wait (ptid_t ptid, struct target_waitstatus *ourstatus,
 		       target_wait_flags options)
@@ -85,6 +98,8 @@ obsd_nat_target::wait (ptid_t ptid, struct target_waitstatus *ourstatus,
       if (ptrace (PT_GET_PROCESS_STATE, pid, (caddr_t)&pe, sizeof pe) == -1)
 	perror_with_name (("ptrace"));
 
+      wptid = ptid_t (pid, pe.pe_tid, 0);
+
       switch (pe.pe_report_event)
 	{
 	case PTRACE_FORK:
@@ -105,13 +120,15 @@ obsd_nat_target::wait (ptid_t ptid, struct target_waitstatus *ourstatus,
 	  if (find_inferior_pid (this, fpid) != nullptr)
 	    {
 	      ourstatus->value.related_pid = ptid_t (pe.pe_other_pid);
-	      return ptid_t (fpid);
+	      wptid = ptid_t (fpid, pe.pe_tid, 0);
 	    }
 
-	  return ptid_t (pid);
+	  obsd_enable_proc_events (ourstatus->value.related_pid.pid ());
+	  break;
 	}
 
-      wptid = ptid_t (pid, pe.pe_tid, 0);
+      /* Ensure the ptid is updated with an LWP id on the first stop
+         of a process.  */
       if (!in_thread_list (this, wptid))
 	{
 	  if (in_thread_list (this, ptid_t (pid)))
@@ -123,34 +140,16 @@ obsd_nat_target::wait (ptid_t ptid, struct target_waitstatus *ourstatus,
   return wptid;
 }
 
-#endif /* PT_GET_THREAD_FIRST */
-
-#ifdef PT_GET_PROCESS_STATE
-
 void
 obsd_nat_target::post_attach (int pid)
 {
-  ptrace_event_t pe;
-
-  /* Set the initial event mask.  */
-  memset (&pe, 0, sizeof pe);
-  pe.pe_set_event |= PTRACE_FORK;
-  if (ptrace (PT_SET_EVENT_MASK, pid,
-	      (PTRACE_TYPE_ARG3)&pe, sizeof pe) == -1)
-    perror_with_name (("ptrace"));
+  obsd_enable_proc_events (pid);
 }
 
 void
 obsd_nat_target::post_startup_inferior (ptid_t pid)
 {
-  ptrace_event_t pe;
-
-  /* Set the initial event mask.  */
-  memset (&pe, 0, sizeof pe);
-  pe.pe_set_event |= PTRACE_FORK;
-  if (ptrace (PT_SET_EVENT_MASK, pid.pid (),
-	      (PTRACE_TYPE_ARG3)&pe, sizeof pe) == -1)
-    perror_with_name (("ptrace"));
+  obsd_enable_proc_events (pid.pid ());
 }
 
 /* Target hook for follow_fork.  On entry and at return inferior_ptid is
@@ -160,7 +159,7 @@ void
 obsd_nat_target::follow_fork (ptid_t child_ptid, target_waitkind fork_kind,
 			      bool follow_child, bool detach_fork)
 {
-  if (!follow_child)
+  if (!follow_child && detach_fork)
     {
       /* Breakpoints have already been detached from the child by
 	 infrun.c.  */
@@ -181,5 +180,3 @@ obsd_nat_target::remove_fork_catchpoint (int pid)
 {
   return 0;
 }
-
-#endif /* PT_GET_PROCESS_STATE */
diff --git a/gdb/obsd-nat.h b/gdb/obsd-nat.h
index ddd4baf..43a793e 100644
--- a/gdb/obsd-nat.h
+++ b/gdb/obsd-nat.h
@@ -29,7 +29,6 @@ class obsd_nat_target : public inf_ptrace_target
   void update_thread_list () override;
   ptid_t wait (ptid_t, struct target_waitstatus *, target_wait_flags) override;
 
-#ifdef PT_GET_PROCESS_STATE
   void follow_fork (ptid_t, target_waitkind, bool, bool) override;
 
   int insert_fork_catchpoint (int) override;
@@ -39,7 +38,6 @@ class obsd_nat_target : public inf_ptrace_target
   void post_startup_inferior (ptid_t) override;
 
   void post_attach (int) override;
-#endif
 };
 
 #endif /* obsd-nat.h */