Fix PR gdb/19858: GDB doesn't register the JIT libraries on attach

Ref: https://sourceware.org/ml/gdb/2016-03/msg00023.html

GDB currently fails to fetch the list of already-registered JIT
modules on attach.

Nothing is calling jit_inferior_init, which is what is responsible for
walking the JIT object list at init time.

Despite the misleading naming, jit_inferior_created_hook ->
jit_inferior_init is only called when the inferior execs.

This regressed with the fix for PR gdb/13431 (03bef283c2d3):
 https://sourceware.org/ml/gdb-patches/2012-02/msg00023.html which
removed the inferior_created (jit_inferior_created_observer)
observer.

Adding an inferior_created observer back fixes the issue.

In turn, this exposes a bug in jit_breakpoint_re_set_internal as well,
which is returning the wrong result when we already have the
breakpoint at the right address.

gdb/ChangeLog:
2016-03-31  Yichao Yu  <yyc1992@gmail.com>

	PR gdb/19858
	* jit.c (jit_breakpoint_re_set_internal): Return 0 if we already
	got the breakpoint at the right address.
	(jit_inferior_created): New function.
	(_initialize_jit): Install jit_inferior_created as
	inferior_created observer.

Signed-off-by: Pedro Alves <palves@redhat.com>

1 files changed, 11 insertions, 2 deletions

diff --git a/gdb/jit.c b/gdb/jit.c
index afc1c517fa7..9fd5ae675b0 100644
--- a/gdb/jit.c
+++ b/gdb/jit.c
@@ -1026,7 +1026,7 @@ jit_breakpoint_deleted (struct breakpoint *b)
 }
 
 /* (Re-)Initialize the jit breakpoint if necessary.
-   Return 0 on success.  */
+   Return 0 if the jit breakpoint has been successfully initialized.  */
 
 static int
 jit_breakpoint_re_set_internal (struct gdbarch *gdbarch,
@@ -1070,7 +1070,7 @@ jit_breakpoint_re_set_internal (struct gdbarch *gdbarch,
 			paddress (gdbarch, addr));
 
   if (ps_data->cached_code_address == addr)
-    return 1;
+    return 0;
 
   /* Delete the old breakpoint.  */
   if (ps_data->jit_breakpoint != NULL)
@@ -1367,6 +1367,14 @@ jit_inferior_init (struct gdbarch *gdbarch)
     }
 }
 
+/* inferior_created observer.  */
+
+static void
+jit_inferior_created (struct target_ops *ops, int from_tty)
+{
+  jit_inferior_created_hook ();
+}
+
 /* Exported routine to call when an inferior has been created.  */
 
 void
@@ -1496,6 +1504,7 @@ _initialize_jit (void)
 			     show_jit_debug,
 			     &setdebuglist, &showdebuglist);
 
+  observer_attach_inferior_created (jit_inferior_created);
   observer_attach_inferior_exit (jit_inferior_exit_hook);
   observer_attach_breakpoint_deleted (jit_breakpoint_deleted);