[PATCH] Fixes in LargeMmapAllocator::GetBlockBegin().

[Sergey Matveev]

    - reverted one change and added a test for the other

Hi kcc, glider, samsonov,

http://llvm-reviews.chandlerc.com/D624

CHANGE SINCE LAST DIFF
  http://llvm-reviews.chandlerc.com/D624?vs=1510&id=1539#toc

Files:
  lib/sanitizer_common/sanitizer_allocator.h
  lib/sanitizer_common/tests/sanitizer_allocator_test.cc

Index: lib/sanitizer_common/sanitizer_allocator.h
===================================================================
--- lib/sanitizer_common/sanitizer_allocator.h
+++ lib/sanitizer_common/sanitizer_allocator.h
@@ -1014,7 +1014,7 @@
     CHECK_GE(nearest_chunk, h->map_beg);
     CHECK_LT(nearest_chunk, h->map_beg + h->map_size);
     CHECK_LE(nearest_chunk, p);
-    if (h->map_beg + h->map_size < p)
+    if (h->map_beg + h->map_size <= p)
       return 0;
     return GetUser(h);
   }
Index: lib/sanitizer_common/tests/sanitizer_allocator_test.cc
===================================================================
--- lib/sanitizer_common/tests/sanitizer_allocator_test.cc
+++ lib/sanitizer_common/tests/sanitizer_allocator_test.cc
@@ -337,6 +337,13 @@
       a.Deallocate(&stats, allocated[i]);
     }
   }
+
+  // Regression test for boundary condition in GetBlockBegin(). 
+  uptr page_size = GetPageSizeCached();
+  char *p = (char *)a.Allocate(&stats, page_size, 1);
+  CHECK_EQ(p, a.GetBlockBegin(p));
+  CHECK_NE(p, (char *)a.GetBlockBegin(p) + page_size);
+  a.Deallocate(&stats, p);
 }
 
 template
@@ -629,7 +636,6 @@
   TestSizeClassAllocatorIteration<Allocator32Compact>();
 }
 
-
 TEST(SanitizerCommon, LargeMmapAllocatorIteration) {
   LargeMmapAllocator<> a;
   a.Init();
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