This libgc patch helped isolate the mono problem


Index: libgc/mark.c
===================================================================
--- libgc/mark.c	(revision 45372)
+++ libgc/mark.c	(working copy)
@@ -636,6 +666,9 @@
 # endif
     current_p = mark_stack_top -> mse_start;
     descr = mark_stack_top -> mse_descr;
+    GC_printf2("process ptr %p: slot %d\n", current_p,
+	       (mark_stack_top - mark_stack));
+
   retry:
     /* current_p and descr describe the current object.		*/
     /* *mark_stack_top is vacant.				*/
@@ -647,6 +680,8 @@
       
       switch(tag) {
         case GC_DS_LENGTH:
+	  GC_printf1(" DS_LENGTH: 0x%x\n", descr);
+
           /* Large length.					        */
           /* Process part of the range to avoid pushing too much on the	*/
           /* stack.							*/
@@ -676,6 +711,7 @@
           limit = (word *)((char *)limit + sizeof(word) - ALIGNMENT);
           break;
         case GC_DS_BITMAP:
+	  GC_printf1(" DS_BITMAP: 0x%x\n", descr);
           mark_stack_top--;
           descr &= ~GC_DS_TAGS;
           credit -= WORDS_TO_BYTES(WORDSZ/2); /* guess */
@@ -694,6 +730,7 @@
           }
           continue;
         case GC_DS_PROC:
+	  GC_printf1(" DS_PROC: 0x%x\n", descr);
           mark_stack_top--;
           credit -= GC_PROC_BYTES;
           mark_stack_top =
@@ -702,6 +739,7 @@
               	    mark_stack_limit, ENV(descr));
           continue;
         case GC_DS_PER_OBJECT:
+	  GC_printf1(" DS_PER_OBJECT: 0x%x\n", descr);
 	  if ((signed_word)descr >= 0) {
 	    /* Descriptor is in the object.	*/
             descr = *(word *)((ptr_t)current_p + descr - GC_DS_PER_OBJECT);
@@ -731,9 +769,20 @@
 	      mark_stack_top--;
 	      continue;
 	  }
+	  /* mono specific amazingly hackish hack */
+	  {
+		  void *MonoClass = *(void **)(*(void **)current_p);
+		  if (MonoClass) {
+			  char *name = *(void **)((unsigned char *)MonoClass + 0x34);
+			  GC_printf6("  Object of type '%s' vtable %p class %p currentp %p has size %d slot %d on stack\n",
+				     name, *(void **)current_p, MonoClass, current_p, descr, (mark_stack_top - mark_stack));
+		  }
+	  }
+
           goto retry;
       }
     } else /* Small object with length descriptor */ {
+      GC_printf1(" DS_SMALL_PER_OBJECT: 0x%x\n", descr);
       mark_stack_top--;
       limit = (word *)(((ptr_t)current_p) + (word)descr);
     }
Index: libgc/include/private/gc_priv.h
===================================================================
--- libgc/include/private/gc_priv.h	(revision 45372)
+++ libgc/include/private/gc_priv.h	(working copy)
@@ -14,7 +14,9 @@
  * provided the above notices are retained, and a notice that the code was
  * modified is included with the above copyright notice.
  */
 
+#define GC_ASSERTIONS 
+
 # ifndef GC_PRIVATE_H
 # define GC_PRIVATE_H
 
@@ -171,7 +172,8 @@
 		    /* whether or not the block was found to be empty      */
 		    /* during the reclaim phase.  Typically generates       */
 		    /* about one screenful per garbage collection.         */
-#undef PRINTBLOCKS
+#define PRINTBLOCKS
+#undef SILENT
 
 #ifdef SILENT
 #  ifdef PRINTSTATS
Index: libgc/include/private/pthread_support.h
===================================================================
--- libgc/include/private/pthread_support.h	(revision 45372)
+++ libgc/include/private/pthread_support.h	(working copy)
@@ -1,6 +1,8 @@
 #ifndef GC_PTHREAD_SUPPORT_H
 #define GC_PTHREAD_SUPPORT_H
 
+#define DEBUG_THREADS 1
+
 # include "private/gc_priv.h"
 
 # if defined(GC_PTHREADS) && !defined(GC_SOLARIS_THREADS) \