Breakpad processor: Fix function and public symbol lookup.

In r480, I botched the change to make the comparisons that decide
whether an address falls within a function's range safe from overflow.
The original code said:

  address >= function_base && address < function_base + function_size

which is fine unless the function abuts the end of the address space,
in which case the addition overflows and you get a false negative.

My change subtracted function_size from both sides of the latter
comparison, which is meaning-preserving in true math, and gets you:

  address >= function_base && address - function_size < function_base

This not only reads strangely, but also still overflows if
function_size is greater than address. That's rare, but I've added a
case to the unit tests that checks it.

My intent had been to replace the addition which could overflow with a
subtraction that was known not to overflow, namely:

  address >= function_base && address - function_base < function_size

This is equivalent to the original in true math, and because of the
first comparison, we know the subtraction won't underflow in MemAddr
math.

The patch includes similar fixes to the public symbol lookup code, and
to FindWindowsFrameInfo, which was the only other function affected by
r480.

a=jimblandy, r=mmentovai


git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@503 4c0a9323-5329-0410-9bdc-e9ce6186880e

3 files changed, 17 insertions, 4 deletions

diff --git a/src/processor/basic_source_line_resolver.cc b/src/processor/basic_source_line_resolver.cc
index 1aff2d1d..0bd17124 100644
--- a/src/processor/basic_source_line_resolver.cc
+++ b/src/processor/basic_source_line_resolver.cc
@@ -442,7 +442,7 @@ void BasicSourceLineResolver::Module::LookupAddress(StackFrame *frame) const {
   MemAddr public_address;
   if (functions_.RetrieveNearestRange(address, &func,
                                       &function_base, &function_size) &&
-      address >= function_base && address - function_size < function_base) {
+      address >= function_base && address - function_base < function_size) {
     frame->function_name = func->name;
     frame->function_base = frame->module->base_address() + function_base;
 
@@ -458,7 +458,7 @@ void BasicSourceLineResolver::Module::LookupAddress(StackFrame *frame) const {
     }
   } else if (public_symbols_.Retrieve(address,
                                       &public_symbol, &public_address) &&
-             (!func.get() || public_address - function_size > function_base)) {
+             (!func.get() || public_address > function_base)) {
     frame->function_name = public_symbol->name;
     frame->function_base = frame->module->base_address() + public_address;
   }
@@ -502,7 +502,7 @@ WindowsFrameInfo *BasicSourceLineResolver::Module::FindWindowsFrameInfo(
   linked_ptr<PublicSymbol> public_symbol;
   MemAddr public_address;
   if (public_symbols_.Retrieve(address, &public_symbol, &public_address) &&
-      (!function.get() || public_address - function_size > function_base)) {
+      (!function.get() || public_address > function_base)) {
     result->parameter_size = public_symbol->parameter_size;
   }
   
diff --git a/src/processor/basic_source_line_resolver_unittest.cc b/src/processor/basic_source_line_resolver_unittest.cc
index 2940831f..45dfe979 100644
--- a/src/processor/basic_source_line_resolver_unittest.cc
+++ b/src/processor/basic_source_line_resolver_unittest.cc
@@ -63,7 +63,7 @@ class TestCodeModule : public CodeModule {
   virtual ~TestCodeModule() {}
 
   virtual u_int64_t base_address() const { return 0; }
-  virtual u_int64_t size() const { return 0x4000; }
+  virtual u_int64_t size() const { return 0xb000; }
   virtual string code_file() const { return code_file_; }
   virtual string code_identifier() const { return ""; }
   virtual string debug_file() const { return ""; }
@@ -162,6 +162,16 @@ static bool RunTests() {
   frame_info.reset(resolver.FindWindowsFrameInfo(&frame));
   ASSERT_FALSE(frame_info.get());
 
+  frame.instruction = 0x2900;
+  frame.module = &module1;
+  resolver.FillSourceLineInfo(&frame);
+  ASSERT_EQ(frame.function_name, string("PublicSymbol"));
+
+  frame.instruction = 0x4000;
+  frame.module = &module1;
+  resolver.FillSourceLineInfo(&frame);
+  ASSERT_EQ(frame.function_name, string("LargeFunction"));
+
   TestCodeModule module2("module2");
 
   frame.instruction = 0x2181;
diff --git a/src/processor/testdata/module1.out b/src/processor/testdata/module1.out
index 85687828..3fb1f181 100644
--- a/src/processor/testdata/module1.out
+++ b/src/processor/testdata/module1.out
@@ -13,6 +13,9 @@ FUNC 1200 100 8 Function1_3
 FUNC 1300 100 c Function1_4
 FUNC 2000 0 0 Test_Zero_Size_Function_Is_Ignored
 2000 4 88 2
+PUBLIC 2800 0 PublicSymbol
+FUNC 3000 7000 42 LargeFunction
+3000 7000 4098359 3
 STACK WIN 4 1000 c 1 0 0 0 0 0 1 $eip 4 + ^ = $esp $ebp 8 + = $ebp $ebp ^ =
 STACK WIN 4 1100 8 1 0 0 0 0 0 1 $eip 4 + ^ = $esp $ebp 8 + = $ebp $ebp ^ =
 STACK WIN 4 1100 100 1 0 0 0 0 0 1 $eip 4 + ^ = $esp $ebp 8 + = $ebp $ebp ^ =