From 702d26018769f9fbc4763c7ed02331aed596ac7d Mon Sep 17 00:00:00 2001
From: Calin Juravle <calin@google.com>
Date: Thu, 30 Apr 2015 19:28:21 +0100
Subject: Skip compilation when falling-through out of method code.

Bug: 19988134
Change-Id: I68638ce9551848a67af587595f264b51f976df11
---
 compiler/optimizing/builder.cc | 24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

(limited to 'compiler/optimizing/builder.cc')

diff --git a/compiler/optimizing/builder.cc b/compiler/optimizing/builder.cc
index 0f44af07b8..a5c6f23343 100644
--- a/compiler/optimizing/builder.cc
+++ b/compiler/optimizing/builder.cc
@@ -282,7 +282,10 @@ bool HGraphBuilder::BuildGraph(const DexFile::CodeItem& code_item) {
 
   // To avoid splitting blocks, we compute ahead of time the instructions that
   // start a new block, and create these blocks.
-  ComputeBranchTargets(code_ptr, code_end, &number_of_branches);
+  if (!ComputeBranchTargets(code_ptr, code_end, &number_of_branches)) {
+    MaybeRecordStat(MethodCompilationStat::kNotCompiledBranchOutsideMethodCode);
+    return false;
+  }
 
   // Note that the compiler driver is null when unit testing.
   if ((compiler_driver_ != nullptr) && SkipCompilation(code_item, number_of_branches)) {
@@ -349,7 +352,7 @@ void HGraphBuilder::MaybeUpdateCurrentBlock(size_t index) {
   current_block_ = block;
 }
 
-void HGraphBuilder::ComputeBranchTargets(const uint16_t* code_ptr,
+bool HGraphBuilder::ComputeBranchTargets(const uint16_t* code_ptr,
                                          const uint16_t* code_end,
                                          size_t* number_of_branches) {
   branch_targets_.SetSize(code_end - code_ptr);
@@ -374,7 +377,14 @@ void HGraphBuilder::ComputeBranchTargets(const uint16_t* code_ptr,
       }
       dex_pc += instruction.SizeInCodeUnits();
       code_ptr += instruction.SizeInCodeUnits();
-      if ((code_ptr < code_end) && (FindBlockStartingAt(dex_pc) == nullptr)) {
+
+      if (code_ptr >= code_end) {
+        if (instruction.CanFlowThrough()) {
+          // In the normal case we should never hit this but someone can artificially forge a dex
+          // file to fall-through out the method code. In this case we bail out compilation.
+          return false;
+        }
+      } else if (FindBlockStartingAt(dex_pc) == nullptr) {
         block = new (arena_) HBasicBlock(graph_, dex_pc);
         branch_targets_.Put(dex_pc, block);
       }
@@ -406,7 +416,12 @@ void HGraphBuilder::ComputeBranchTargets(const uint16_t* code_ptr,
       // Fall-through. Add a block if there is more code afterwards.
       dex_pc += instruction.SizeInCodeUnits();
       code_ptr += instruction.SizeInCodeUnits();
-      if ((code_ptr < code_end) && (FindBlockStartingAt(dex_pc) == nullptr)) {
+      if (code_ptr >= code_end) {
+        // In the normal case we should never hit this but someone can artificially forge a dex
+        // file to fall-through out the method code. In this case we bail out compilation.
+        // (A switch can fall-through so we don't need to check CanFlowThrough().)
+        return false;
+      } else if (FindBlockStartingAt(dex_pc) == nullptr) {
         block = new (arena_) HBasicBlock(graph_, dex_pc);
         branch_targets_.Put(dex_pc, block);
       }
@@ -415,6 +430,7 @@ void HGraphBuilder::ComputeBranchTargets(const uint16_t* code_ptr,
       dex_pc += instruction.SizeInCodeUnits();
     }
   }
+  return true;
 }
 
 HBasicBlock* HGraphBuilder::FindBlockStartingAt(int32_t index) const {
-- 
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