Re: PR13901

[Pedro Alves <palves@redhat.com>]

On 04/03/2012 08:28 AM, John Gilmore wrote:

>> If we can't skip darwin_set_sstep for all continues that are not single-steps,
>> we could at least skip those while starting up (when continuing the shell
>> until we see enough execs).  That'd suggest a new flag like
>> darwin-nat.h:struct private_inferior->starting_up, set and cleared in
>> darwin_create_inferior, and then making darwin_resume_thread do ...
> 
> When I was maintaining GDB (many years ago), touching *anything* in
> the state machine that figured out what to do next when the inferior
> stopped was guaranteed to produce several bugs for every fix.

> In the changes we made, I tried to reduce that tendency, and make

> the code more modular and less fragile.  Today, "just" adding a new
> flag for this may be as simple as you hope.


Oh, a challenge!  ;-)

I think this should work, but I'm not set up for testing it...

As noted in a comment below, this isn't just about the shell; a
"set exec-wrapper WRAPPER" wrapper of the wrong bitness should also
trigger the original problem.

2012-04-04  Pedro Alves  <palves@redhat.com>

	* darwin-nat.c (darwin_resume_thread): Don't set the thread to
	single-step if the inferior is still starting up.
	(darwin_ptrace_him): Set and clear the new starting_up flag.
	* darwin-nat.h (struct private_inferior) <starting_up>: New flag.
---

 gdb/darwin-nat.c |   18 ++++++++++++++----
 gdb/darwin-nat.h |    4 ++++
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/gdb/darwin-nat.c b/gdb/darwin-nat.c
index 010700c..bdd174b 100644
--- a/gdb/darwin-nat.c
+++ b/gdb/darwin-nat.c
@@ -705,10 +705,18 @@ darwin_resume_thread (struct inferior *inf, darwin_thread_t *thread,
 	  thread->signaled = 1;
 	}

-      /* Set single step.  */
-      inferior_debug (4, _("darwin_set_sstep (thread=%x, enable=%d)\n"),
-                      thread->gdb_port, step);
-      darwin_set_sstep (thread->gdb_port, step);
+      /* If our target process hasn't been exec'ed yet, when avoid
+	 accessing anything in the inferior (registers, memory, etc.).
+	 We might have spawned a 64-bit shell while debugging a 32-bit
+	 program.  */
+      gdb_assert (!inf->private->starting_up || !step);
+      if (!inf->private->starting_up)
+	{
+	  /* Set single step.  */
+	  inferior_debug (4, _("darwin_set_sstep (thread=%x, enable=%d)\n"),
+			  thread->gdb_port, step);
+	  darwin_set_sstep (thread->gdb_port, step);
+	}
       thread->single_step = step;

       darwin_send_reply (inf, thread);
@@ -1505,7 +1513,9 @@ darwin_ptrace_him (int pid)

   darwin_init_thread_list (inf);

+  inf->private->starting_up = 1;
   startup_inferior (START_INFERIOR_TRAPS_EXPECTED);
+  inf->private->starting_up = 0;
 }

 static void
diff --git a/gdb/darwin-nat.h b/gdb/darwin-nat.h
index 6c89299..d9d4e33 100644
--- a/gdb/darwin-nat.h
+++ b/gdb/darwin-nat.h
@@ -126,6 +126,10 @@ struct private_inferior

   /* Sorted vector of known threads.  */
   VEC(darwin_thread_t) *threads;
+
+  /* True if starting up (going through the shell, or an
+     exec-wrapper).  */
+  int starting_up;
 };
 typedef struct private_inferior darwin_inferior;