[MinGW] RFA: Fix GetCallerInfo() for Targets Using SJLJ EH

[Ranjit Mathew <rmathew at gmail dot com>]

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Hi,

  _Jv_StackTrace::GetCallerInfo() in stacktrace.cc does not
do anything if the target uses SJLJ EH. The attached patch
proposes to fix this. It also changes fallback_backtrace()
in sysdep/i386/backtrace.h to call the trace callback
function in STATE, if any, and to update STATE->POS with
every frame rather than once at the end.

It seems difficult to exercise this code path though.
Class.forName() doesn't use this function any more and
it indeed works for MinGW even without this patch.
Class.getClassLoader() also seems to ordinarily bypass
this function.

Tested via an i686-pc-linux-gnu to i686-pc-mingw32
cross-compiler.

OK to apply to trunk?

Thanks,
Ranjit.

- --
Ranjit Mathew       Email: rmathew AT gmail DOT com

Bangalore, INDIA.     Web: http://rmathew.com/




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Index: ChangeLog
from  Ranjit Mathew  <rmathew@gcc.gnu.org>

	* stacktrace.cc (_Jv_StackTrace::GetCallerInfo): Use
	fallback_backtrace() for targets using SJLJ EH.
	* sysdep/i386/backtrace.h (fallback_backtrace): If STATE has a
	trace callback function, call it for every frame.  Update STATE->POS
	for every frame instead of once at the end of the backtrace process.

Index: stacktrace.cc
===================================================================
--- stacktrace.cc	(revision 115260)
+++ stacktrace.cc	(working copy)
@@ -421,7 +421,6 @@ void
 _Jv_StackTrace::GetCallerInfo (jclass checkClass, jclass *caller_class,
   _Jv_Method **caller_meth)
 {
-#ifndef SJLJ_EXCEPTIONS
   int trace_size = 20;
   _Jv_StackFrame frames[trace_size];
   _Jv_UnwindState state (trace_size);
@@ -439,15 +438,18 @@ _Jv_StackTrace::GetCallerInfo (jclass ch
   //JvSynchronized (ncodeMap);
   UpdateNCodeMap ();
 
+#ifdef SJLJ_EXCEPTIONS
+  // The Unwind interface doesn't work with the SJLJ exception model.
+  // Fall back to a platform-specific unwinder.
+  fallback_backtrace (&state);
+#else /* SJLJ_EXCEPTIONS */  
   _Unwind_Backtrace (UnwindTraceFn, &state);
+#endif /* SJLJ_EXCEPTIONS */
   
   if (caller_class)
     *caller_class = trace_data.foundClass;
   if (caller_meth)
     *caller_meth = trace_data.foundMeth;
-#else
-  return;
-#endif
 }
 
 // Return a java array containing the Java classes on the stack above CHECKCLASS.
Index: sysdep/i386/backtrace.h
===================================================================
--- sysdep/i386/backtrace.h	(revision 115261)
+++ sysdep/i386/backtrace.h	(working copy)
@@ -66,6 +66,10 @@ fallback_backtrace (_Jv_UnwindState *sta
               && scan_bytes[2] == 0xE5)
             {
               state->frames[i].start_ip = (void *)scan_addr;
+
+              if (state->trace_function != NULL)
+                (state->trace_function) (state);
+
               break;
             }
         }
@@ -75,7 +79,7 @@ fallback_backtrace (_Jv_UnwindState *sta
         break;
 
       i++;
+      state->pos = i;
     }
-  state->pos = i;
 }
 #endif