commit f6dd829292b451a0eaaf339964fcf9ebc804897b
author Andreas Gampe <agampe@google.com> Fri Aug 19 20:22:19 2016 -0700
committer Andreas Gampe <agampe@google.com> Fri Aug 19 20:45:04 2016 -0700
tree f266ae41051125f4fea558bbfa87c617f9d5ac9b
parent da0f5e72cc5f2747a330b21afa34e7d798fc5c54

ART: Enforce arena alignment in Realloc

Enforce the expected alignment in Realloc when the given buffer
can be expanded.

Add debug checks to prove alignment guarantees.

Change-Id: I7dbaf3ca0896f714cff07ff08f067a7c088a6c8d
Test: m test-art-host

runtime/base/arena_allocator.cc

diff --git a/runtime/base/arena_allocator.cc b/runtime/base/arena_allocator.cc
index b84e29f..aeb990c 100644
--- a/runtime/base/arena_allocator.cc
+++ b/runtime/base/arena_allocator.cc
@@ -163,6 +163,7 @@
 MallocArena::MallocArena(size_t size) {
   memory_ = reinterpret_cast<uint8_t*>(calloc(1, size));
   CHECK(memory_ != nullptr);  // Abort on OOM.
+  DCHECK_ALIGNED(memory_, ArenaAllocator::kAlignment);
   size_ = size;
 }
 
@@ -370,6 +371,7 @@
     arena_head_ = new_arena;
     // Update our internal data structures.
     begin_ = new_arena->Begin();
+    DCHECK_ALIGNED(begin_, kAlignment);
     ptr_ = begin_ + bytes;
     end_ = new_arena->End();
   }

runtime/base/arena_allocator.h

diff --git a/runtime/base/arena_allocator.h b/runtime/base/arena_allocator.h
index 6c1a898..3fad96b 100644
--- a/runtime/base/arena_allocator.h
+++ b/runtime/base/arena_allocator.h
@@ -310,6 +310,7 @@
       return AllocFromNewArena(bytes);
     }
     uint8_t* ret = ptr_;
+    DCHECK_ALIGNED(ret, kAlignment);
     ptr_ += bytes;
     return ret;
   }
@@ -319,20 +320,24 @@
                 ArenaAllocKind kind = kArenaAllocMisc) ALWAYS_INLINE {
     DCHECK_GE(new_size, ptr_size);
     DCHECK_EQ(ptr == nullptr, ptr_size == 0u);
-    auto* end = reinterpret_cast<uint8_t*>(ptr) + ptr_size;
+    // We always allocate aligned.
+    const size_t aligned_ptr_size = RoundUp(ptr_size, kAlignment);
+    auto* end = reinterpret_cast<uint8_t*>(ptr) + aligned_ptr_size;
     // If we haven't allocated anything else, we can safely extend.
     if (end == ptr_) {
       DCHECK(!IsRunningOnMemoryTool());  // Red zone prevents end == ptr_.
-      const size_t size_delta = new_size - ptr_size;
+      const size_t aligned_new_size = RoundUp(new_size, kAlignment);
+      const size_t size_delta = aligned_new_size - aligned_ptr_size;
       // Check remain space.
       const size_t remain = end_ - ptr_;
       if (remain >= size_delta) {
         ptr_ += size_delta;
         ArenaAllocatorStats::RecordAlloc(size_delta, kind);
+        DCHECK_ALIGNED(ptr_, kAlignment);
         return ptr;
       }
     }
-    auto* new_ptr = Alloc(new_size, kind);
+    auto* new_ptr = Alloc(new_size, kind);  // Note: Alloc will take care of aligning new_size.
     memcpy(new_ptr, ptr, ptr_size);
     // TODO: Call free on ptr if linear alloc supports free.
     return new_ptr;
@@ -362,11 +367,12 @@
 
   bool Contains(const void* ptr) const;
 
+  static constexpr size_t kAlignment = 8;
+
  private:
   void* AllocWithMemoryTool(size_t bytes, ArenaAllocKind kind);
   uint8_t* AllocFromNewArena(size_t bytes);
 
-  static constexpr size_t kAlignment = 8;
 
   void UpdateBytesAllocated();