tenderlove	2018-04-27 07:49:00 +0900 (Fri, 27 Apr 2018)

  New Revision: 63265

  https://svn.ruby-lang.org/cgi-bin/viewvc.cgi?view=revision&revision=63265

  Log:
    Fix use of `rb_profile_frames` start parameter
    
    rb_profile_frames was always behaving as if the value given for the
    start parameter was 0.
    
    The reason for this was that it would check if (start > 0) { then
    continue without updating the control frame pointer or anything other
    than decrementing start.
    
    [ruby-core:86147] [Bug #14607]
    
    Co-authored-by: Dylan Thacker-Smith <Dylan.Smith@s...>

  Modified files:
    trunk/test/-ext-/debug/test_profile_frames.rb
    trunk/vm_backtrace.c
Index: test/-ext-/debug/test_profile_frames.rb
===================================================================
--- test/-ext-/debug/test_profile_frames.rb	(revision 63264)
+++ test/-ext-/debug/test_profile_frames.rb	(revision 63265)
@@ -119,4 +119,8 @@ class TestProfileFrames < Test::Unit::Te https://github.com/ruby/ruby/blob/trunk/test/-ext-/debug/test_profile_frames.rb#L119
       a
     end;
   end
+
+  def test_start
+    assert_equal Bug::Debug.profile_frames(0, 10).tap(&:shift), Bug::Debug.profile_frames(1, 9)
+  end
 end
Index: vm_backtrace.c
===================================================================
--- vm_backtrace.c	(revision 63264)
+++ vm_backtrace.c	(revision 63265)
@@ -1276,7 +1276,7 @@ rb_profile_frames(int start, int limit, https://github.com/ruby/ruby/blob/trunk/vm_backtrace.c#L1276
     const rb_control_frame_t *cfp = ec->cfp, *end_cfp = RUBY_VM_END_CONTROL_FRAME(ec);
     const rb_callable_method_entry_t *cme;
 
-    for (i=0; i<limit && cfp != end_cfp;) {
+    for (i=0; i<limit && cfp != end_cfp; cfp = RUBY_VM_PREVIOUS_CONTROL_FRAME(cfp)) {
 	if (cfp->iseq && cfp->pc) {
 	    if (start > 0) {
 		start--;
@@ -1296,7 +1296,6 @@ rb_profile_frames(int start, int limit, https://github.com/ruby/ruby/blob/trunk/vm_backtrace.c#L1296
 
 	    i++;
 	}
-	cfp = RUBY_VM_PREVIOUS_CONTROL_FRAME(cfp);
     }
 
     return i;

--
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