[RFA 4/5] Darwin: fix thread ptid started by fork_inferior

[Xavier Roirand <roirand@adacore.com>]

When debugging a program on Mac OS X Darwin, gdb stops with:

Temporary breakpoint 1 at 0x100000fb4: file /tmp/helloworld.c, line 1.
Starting program: /private/tmp/helloworld
[New Thread 0xb03 of process 65066]
[New Thread 0xd03 of process 65066]
During startup program terminated with signal SIGTRAP, Trace/breakpoint trap.

When the inferior is started a thread with lwp=tid=0 is created
and has to be fixed later by darwin_init_thread_list(). Because
this is not done, GDB does not understand that the SIGTRAP is
coming from GDB and not the program itself.

gdb/ChangeLog:

        * darwin-nat.c (darwin_check_new_threads): Check if first
        silent thread case.
        (darwin_init_thread_list): Fixup thread ptid.
        (darwin_ptrace_him): Add call.
        (darwin_nat_target::attach): Add call.

Change-Id: Ie8ad7edfff167a1f95140907c75af45ceb3fae14
---
 gdb/darwin-nat.c | 31 ++++++++++++++++++++++++++++---
 1 file changed, 28 insertions(+), 3 deletions(-)

diff --git a/gdb/darwin-nat.c b/gdb/darwin-nat.c
index 96f70cf..9ad4a87 100644
--- a/gdb/darwin-nat.c
+++ b/gdb/darwin-nat.c
@@ -344,8 +344,22 @@ darwin_check_new_threads (struct inferior *inf)
 	  pti->gdb_port = new_id;
 	  pti->msg_state = DARWIN_RUNNING;
 
-	  /* Add the new thread.  */
-	  add_thread_with_info (ptid_t (inf->pid, 0, new_id), pti);
+	  if (old_nbr == 0 && new_ix == 0)
+            {
+	      /* A ptid is created when the inferior is started (see
+                 fork-child.c) with lwp=tid=0.  This ptid will be renamed
+                 later by darwin_init_thread_list (), so find this previous
+                 thread silently added.  */
+
+              struct thread_info *tp = find_thread_ptid (ptid_t (inf->pid, 0, 0));
+              tp->priv.reset (pti);
+            }
+          else
+            {
+              /* Add the new thread.  */
+              add_thread_with_info (ptid_t (inf->pid, 0, new_id), pti);
+             }
+
 	  new_thread_vec.push_back (pti);
 	  new_ix++;
 	  continue;
@@ -1733,6 +1747,8 @@ thread_info_from_private_thread_info (darwin_thread_info *pti)
 static void
 darwin_init_thread_list (struct inferior *inf)
 {
+  ptid_t new_ptid;
+
   darwin_check_new_threads (inf);
 
   darwin_inferior *priv = get_darwin_inferior (inf);
@@ -1743,7 +1759,11 @@ darwin_init_thread_list (struct inferior *inf)
   struct thread_info *first_thread
     = thread_info_from_private_thread_info (first_pti);
 
-  inferior_ptid = first_thread->ptid;
+  /* Note: fork_inferior automatically add a thread but it uses a wrong ptid.
+     Fix up.  */
+  new_ptid = ptid_t (inf->pid, 0, first_pti->gdb_port);
+  thread_change_ptid (inferior_ptid, new_ptid);
+  inferior_ptid = new_ptid;
 }
 
 /* The child must synchronize with gdb: gdb must set the exception port
@@ -1806,6 +1826,9 @@ darwin_ptrace_him (int pid)
   int traps_expected;
   struct inferior *inf = current_inferior ();
 
+  inferior_ptid = ptid_t (pid);
+  add_thread_silent (inferior_ptid);
+
   darwin_attach_pid (inf);
 
   /* Let's the child run.  */
@@ -1933,6 +1956,8 @@ darwin_nat_target::attach (const char *args, int from_tty)
   inferior_appeared (inf, pid);
   inf->attach_flag = 1;
 
+  add_thread_silent (inferior_ptid);
+
   darwin_attach_pid (inf);
 
   darwin_suspend_inferior (inf);
-- 
2.7.4