From 9d4dcf615ab93aca8e0909440841bac5c9057e73 Mon Sep 17 00:00:00 2001
From: Nicholas Nethercote <nnethercote@mozilla.com>
Date: Thu, 11 Jun 2015 18:23:26 -0700
Subject: [PATCH] Bug 1174046 - Fix PLDHashTable::Iterator in chaos mode again.
 r=froydnj, a=philor CLOSED TREE

If you use PLDHashTable::Iterator in chaos mode with a table with zero
capacity, a |% 0| operation takes place in randomUint32LessThan. This change
avoids that.
---
 mfbt/ChaosMode.h       | 1 +
 xpcom/glue/pldhash.cpp | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/mfbt/ChaosMode.h b/mfbt/ChaosMode.h
index 9378f665154..ca943a1e76f 100644
--- a/mfbt/ChaosMode.h
+++ b/mfbt/ChaosMode.h
@@ -81,6 +81,7 @@ public:
    */
   static uint32_t randomUint32LessThan(uint32_t aBound)
   {
+    MOZ_ASSERT(aBound != 0);
     return uint32_t(rand()) % aBound;
   }
 };
diff --git a/xpcom/glue/pldhash.cpp b/xpcom/glue/pldhash.cpp
index ac3f080d79f..c7f22d83736 100644
--- a/xpcom/glue/pldhash.cpp
+++ b/xpcom/glue/pldhash.cpp
@@ -910,7 +910,7 @@ PLDHashTable::Iterator::Iterator(const PLDHashTable* aTable)
   // mEntryAddr, respectively.
   uint32_t capacity = mTable->Capacity();
 
-  if (ChaosMode::isActive(ChaosMode::HashTableIteration)) {
+  if (ChaosMode::isActive(ChaosMode::HashTableIteration) && capacity > 0) {
     // Start iterating at a random point in the hashtable. It would be
     // even more chaotic to iterate in fully random order, but that's a lot
     // more work.