X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=rts%2FHeapStackCheck.cmm;h=a1b6d65f34f6e611b67bb1cbd05dcba0683e041a;hb=de75026f5a48d3d052135a973ab4dff76c5b20f5;hp=10baca23c6789552545ab54fed485ff1c4e2579c;hpb=304e7fb703e7afddc1ef9be6aab6505e36b63b06;p=ghc-hetmet.git

diff --git a/rts/HeapStackCheck.cmm b/rts/HeapStackCheck.cmm
index 10baca2..a1b6d65 100644
--- a/rts/HeapStackCheck.cmm
+++ b/rts/HeapStackCheck.cmm
@@ -26,6 +26,17 @@ import LeaveCriticalSection;
  *    - If HpLim==0, indicating that we should context-switch, we yield
  *      to the scheduler (return ThreadYielding).
  *
+ * Note that we must leave no slop in the heap (this is a requirement
+ * for LDV profiling, at least), so if we just had a heap-check
+ * failure, then we must retract Hp by HpAlloc.  How do we know
+ * whether there was a heap-check failure?  HpLim might be zero, and
+ * yet we got here as a result of a stack-check failure.  Hence, we
+ * require that HpAlloc is only non-zero if there was a heap-check
+ * failure, otherwise it is zero, so we can always safely subtract
+ * HpAlloc from Hp.
+ *
+ * Hence, HpAlloc is zeroed in LOAD_THREAD_STATE().
+ *
  *    - If the context_switch flag is set (the backup plan if setting HpLim
  *      to 0 didn't trigger a context switch), we yield to the scheduler
  *	(return ThreadYielding).
@@ -63,13 +74,14 @@ import LeaveCriticalSection;
 #define GC_GENERIC						\
     DEBUG_ONLY(foreign "C" heapCheckFail());			\
     if (Hp > HpLim) {						\
+        Hp = Hp - HpAlloc/*in bytes*/;				\
         if (HpLim == 0) { \
                 R1 = ThreadYielding;				\
                 goto sched;					\
         }						\
-        Hp = Hp - HpAlloc/*in bytes*/;				\
         if (HpAlloc <= BLOCK_SIZE				\
             && bdescr_link(CurrentNursery) != NULL) {		\
+            HpAlloc = 0;                                        \
             CLOSE_NURSERY();					\
             CurrentNursery = bdescr_link(CurrentNursery);	\
             OPEN_NURSERY();					\