From fd48b7d5586189173f3d45d0b98952ab59d301cd Mon Sep 17 00:00:00 2001
From: Kostya Serebryany <kcc@google.com>
Date: Wed, 29 Aug 2018 21:28:14 +0000
Subject: [PATCH] [hwasan] simplify the realloc implementation: always
 allocate/deallocate on realloc. This may slowdown some realloc-heavy code,
 but at least at this point a want simpler code. Also added a test

llvm-svn: 340973
---
 compiler-rt/lib/hwasan/hwasan_allocator.cc        | 34 +++++-----------------
 compiler-rt/lib/hwasan/hwasan_flags.inc           |  1 -
 compiler-rt/test/hwasan/TestCases/realloc-test.cc | 35 +++++++++++++++++++++++
 3 files changed, 42 insertions(+), 28 deletions(-)
 create mode 100644 compiler-rt/test/hwasan/TestCases/realloc-test.cc

diff --git a/compiler-rt/lib/hwasan/hwasan_allocator.cc b/compiler-rt/lib/hwasan/hwasan_allocator.cc
index 5d3595b..ba5bf0e1 100644
--- a/compiler-rt/lib/hwasan/hwasan_allocator.cc
+++ b/compiler-rt/lib/hwasan/hwasan_allocator.cc
@@ -228,35 +228,15 @@ void *HwasanReallocate(StackTrace *stack, void *user_old_p, uptr new_size,
   if (!PointerAndMemoryTagsMatch(user_old_p))
     ReportInvalidFree(stack, reinterpret_cast<uptr>(user_old_p));
 
-  void *old_p = GetAddressFromPointer(user_old_p);
-  Metadata *meta = reinterpret_cast<Metadata*>(allocator.GetMetaData(old_p));
-  uptr old_size = meta->requested_size;
-  uptr actually_allocated_size = allocator.GetActuallyAllocatedSize(old_p);
-  if (new_size <= actually_allocated_size) {
-    // We are not reallocating here.
-    // FIXME: update stack trace for the allocation?
-    meta->requested_size = new_size;
-    if (!atomic_load_relaxed(&hwasan_allocator_tagging_enabled))
-      return user_old_p;
-    if (flags()->retag_in_realloc) {
-      HwasanThread *t = GetCurrentThread();
-      return (void *)TagMemoryAligned(
-          (uptr)old_p, new_size,
-          t ? t->GenerateRandomTag() : kFallbackAllocTag);
-    }
-    if (new_size > old_size) {
-      tag_t tag = GetTagFromPointer(reinterpret_cast<uptr>(user_old_p));
-      TagMemoryAligned((uptr)old_p + old_size, new_size - old_size, tag);
-    }
-    return user_old_p;
-  }
-  uptr memcpy_size = Min(new_size, old_size);
   void *new_p = HwasanAllocate(stack, new_size, alignment, false /*zeroise*/);
-  if (new_p) {
-    internal_memcpy(new_p, old_p, memcpy_size);
-    HwasanDeallocate(stack, old_p);
+  if (user_old_p && new_p) {
+    void *untagged_ptr_old =  GetAddressFromPointer(user_old_p);
+    Metadata *meta =
+        reinterpret_cast<Metadata *>(allocator.GetMetaData(untagged_ptr_old));
+    internal_memcpy(GetAddressFromPointer(new_p), untagged_ptr_old,
+                    Min(new_size, static_cast<uptr>(meta->requested_size)));
+    HwasanDeallocate(stack, user_old_p);
   }
-  // FIXME: update t->heap_allocations or simplify HwasanReallocate.
   return new_p;
 }
 
diff --git a/compiler-rt/lib/hwasan/hwasan_flags.inc b/compiler-rt/lib/hwasan/hwasan_flags.inc
index 7a474ae..cd04f53 100644
--- a/compiler-rt/lib/hwasan/hwasan_flags.inc
+++ b/compiler-rt/lib/hwasan/hwasan_flags.inc
@@ -19,7 +19,6 @@
 
 HWASAN_FLAG(bool, tag_in_malloc, true, "")
 HWASAN_FLAG(bool, tag_in_free, true, "")
-HWASAN_FLAG(bool, retag_in_realloc, true, "")
 HWASAN_FLAG(bool, print_stats, false, "")
 HWASAN_FLAG(bool, halt_on_error, true, "")
 HWASAN_FLAG(bool, atexit, false, "")
diff --git a/compiler-rt/test/hwasan/TestCases/realloc-test.cc b/compiler-rt/test/hwasan/TestCases/realloc-test.cc
new file mode 100644
index 0000000..23bc619
--- /dev/null
+++ b/compiler-rt/test/hwasan/TestCases/realloc-test.cc
@@ -0,0 +1,35 @@
+// Test basic realloc functionality.
+// RUN: %clang_hwasan %s -o %t
+// RUN: %run %t
+
+#include <stdlib.h>
+#include <assert.h>
+
+int main() {
+  char *x = (char*)realloc(nullptr, 4);
+  x[0] = 10;
+  x[1] = 20;
+  x[2] = 30;
+  x[3] = 40;
+  char *x1 = (char*)realloc(x, 5);
+  assert(x1 != x);  // not necessary true for C,
+                    // but true today for hwasan.
+  assert(x1[0] == 10 && x1[1] == 20 && x1[2] == 30 && x1[3] == 40);
+  x1[4] = 50;
+
+  char *x2 = (char*)realloc(x1, 6);
+  x2[5] = 60;
+  assert(x2 != x1);
+  assert(x2[0] == 10 && x2[1] == 20 && x2[2] == 30 && x2[3] == 40 &&
+         x2[4] == 50 && x2[5] == 60);
+
+  char *x3 = (char*)realloc(x2, 6);
+  assert(x3 != x2);
+  assert(x3[0] == 10 && x3[1] == 20 && x3[2] == 30 && x3[3] == 40 &&
+         x3[4] == 50 && x3[5] == 60);
+
+  char *x4 = (char*)realloc(x3, 5);
+  assert(x4 != x3);
+  assert(x4[0] == 10 && x4[1] == 20 && x4[2] == 30 && x4[3] == 40 &&
+         x4[4] == 50);
+}
-- 
2.7.4