From 7eda134fa7733e84424359c6ac23cd4ce1045435 Mon Sep 17 00:00:00 2001
From: Alexey Samsonov <samsonov@google.com>
Date: Mon, 28 Jan 2013 11:24:13 +0000
Subject: [PATCH] [ASan] fix a bug in allocator-v2 which could lead to SEGV on
 realloc(malloc(0), 4)

llvm-svn: 173681
---
 compiler-rt/lib/asan/asan_allocator2.cc | 2 +-
 compiler-rt/lib/asan/tests/asan_test.cc | 9 +++++++++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/compiler-rt/lib/asan/asan_allocator2.cc b/compiler-rt/lib/asan/asan_allocator2.cc
index 63cb41b4c97c..eae4bf5ee0de 100644
--- a/compiler-rt/lib/asan/asan_allocator2.cc
+++ b/compiler-rt/lib/asan/asan_allocator2.cc
@@ -612,7 +612,7 @@ void *asan_calloc(uptr nmemb, uptr size, StackTrace *stack) {
 }
 
 void *asan_realloc(void *p, uptr size, StackTrace *stack) {
-  if (p == 0)
+  if (p == 0 || reinterpret_cast<uptr>(p) == kReturnOnZeroMalloc)
     return Allocate(size, 8, stack, FROM_MALLOC);
   if (size == 0) {
     Deallocate(p, stack, FROM_MALLOC);
diff --git a/compiler-rt/lib/asan/tests/asan_test.cc b/compiler-rt/lib/asan/tests/asan_test.cc
index 487ed97a5742..f7b6097e4bfc 100644
--- a/compiler-rt/lib/asan/tests/asan_test.cc
+++ b/compiler-rt/lib/asan/tests/asan_test.cc
@@ -380,6 +380,15 @@ TEST(AddressSanitizer, ReallocTest) {
         (my_rand() % 1000 + kMinElem) * sizeof(int));
     EXPECT_EQ(3, ptr[3]);
   }
+  free(ptr);
+  // Realloc pointer returned by malloc(0).
+  int *ptr2 = Ident((int*)malloc(0));
+  fprintf(stderr, "Malloc(0): %p\n", ptr2);
+  ptr2 = Ident((int*)realloc(ptr2, sizeof(*ptr2)));
+  fprintf(stderr, "Realloc(0, 4): %p\n", ptr2);
+  *ptr2 = 42;
+  EXPECT_EQ(42, *ptr2);
+  free(ptr2);
 }
 
 #ifndef __APPLE__