Bugfix: PAPI_list_events

[nsmeds]

I just now found out that PAPI_list_events() does not follow its own specs

The current code (5.1.0.2) will never return the number of events in the eventset unless the supplied array (and thus the size argument) is larger than the event set. The man page clearly states that the returned number may be greater than the array size if the event set does not fit in the supplied array. In particular the call PAPI_list_events(EventSet, NULL, &n) should be allowed if n=0 at the time of the call.

Now, this may break some existing code out there but this is the only way in the spec to get the event set size so I argue it should be fixed. The case where things may get broken in existing code is when the caller supplies arguments with an array that does not fit the whole event set and trusts that the returned number of events is the numer of written entries written into the event array and not the number of available events in the real event set.

Since I have no code that relies on the above behaviour I think we should fix the library to follow its spec and that way find out who has programmed their apps according to library behaviour and not library spec

Cheers,
/Nils

Code: Select all

--- orig/papi.c   2013-01-15 21:44:44.000000000 +0100
+++ patched/papi.c   2013-03-21 10:12:38.999322342 +0100
@@ -5882,26 +5882,36 @@ PAPI_remove_events( int EventSet, int *E
 int
 PAPI_list_events( int EventSet, int *Events, int *number )
 {
+   int maxEvents = *number;
    EventSetInfo_t *ESI;
    int i, j;
 
-   if ( ( Events == NULL ) || ( *number <= 0 ) )
+   if ( ( number == NULL ) || ( *number < 0 ) )
       papi_return( PAPI_EINVAL );
 
    ESI = _papi_hwi_lookup_EventSet( EventSet );
    if ( !ESI )
       papi_return( PAPI_ENOEVST );
 
+   /* The spec states that we always return the number of events in the event set */
+   *number = ESI->NumberOfEvents;
+
+   if ( maxEvents == 0 )
+      papi_return( PAPI_OK );
+
+   /* We better have a valid pointer now that we are going to write stuff */
+   if ( Events == NULL )
+      papi_return( PAPI_EINVAL );
+
    for ( i = 0, j = 0; j < ESI->NumberOfEvents; i++ ) {
       if ( ( int ) ESI->EventInfoArray[i].event_code != PAPI_NULL ) {
          Events[j] = ( int ) ESI->EventInfoArray[i].event_code;
          j++;
-         if ( j == *number )
+         if ( j == maxEvents )
             break;
       }
    }
 
-   *number = j;
 
    return ( PAPI_OK );
 }