[Courgette] Clean up Disassembler; fix ELF Memory leaks.

Cleaning up code surrounding Disassembler:
- Extract AddressTranslator interface to be used across subclasses.
- Use FileOffset = size_t by context.
- Detailed comments & TODOs in DisassemblerElf32ARM.
- Fix DisassemblerElf32ARM memory leaks.
- Lots of superficial stylistic changes.

Except for AddressTranslator routines and unit tests, shying away
from control flow and logic changes.

BUG=579206

Committed: https://crrev.com/58b822d441f5c982e879e536fa3c1cbac8fd339a
Cr-Commit-Position: refs/heads/master@{#380881}

Review URL: https://codereview.chromium.org/1676683002

Cr-Commit-Position: refs/heads/master@{#380987}

courgette/disassembler.cc

@@ -4,24 +4,34 @@
 
 #include "courgette/disassembler.h"
 
+#include "base/logging.h"
+
 namespace courgette {
 
 Disassembler::Disassembler(const void* start, size_t length)
-  : failure_reason_("uninitialized") {
+    : failure_reason_("uninitialized") {
   start_ = reinterpret_cast<const uint8_t*>(start);
   length_ = length;
   end_ = start_ + length_;
 };
 
 Disassembler::~Disassembler() {};
 
-const uint8_t* Disassembler::OffsetToPointer(size_t offset) const {
-  assert(start_ + offset <= end_);
-  return start_ + offset;
+const uint8_t* Disassembler::FileOffsetToPointer(FileOffset file_offset) const {
+  CHECK_LE(file_offset, static_cast<FileOffset>(end_ - start_));
+  return start_ + file_offset;
+}
+
+const uint8_t* Disassembler::RVAToPointer(RVA rva) const {
+  FileOffset file_offset = RVAToFileOffset(rva);
+  if (file_offset == kNoFileOffset)
+    return nullptr;
+
+  return FileOffsetToPointer(file_offset);
 }
 
 bool Disassembler::Good() {
-  failure_reason_ = NULL;
+  failure_reason_ = nullptr;
   return true;
 }
 

courgette/disassembler.h

@@ -16,33 +16,35 @@ namespace courgette {
 
 class AssemblyProgram;
 
-class Disassembler {
+class Disassembler : public AddressTranslator {
  public:
   virtual ~Disassembler();
 
-  virtual ExecutableType kind() { return EXE_UNKNOWN; }
+  // AddressTranslator interfaces.
+  virtual RVA FileOffsetToRVA(FileOffset file_offset) const override = 0;
+  virtual FileOffset RVAToFileOffset(RVA rva) const override = 0;
+  const uint8_t* FileOffsetToPointer(FileOffset file_offset) const override;
+  const uint8_t* RVAToPointer(RVA rva) const override;
 
-  // ok() may always be called but returns 'true' only after ParseHeader
-  // succeeds.
-  bool ok() const { return failure_reason_ == NULL; }
+  virtual ExecutableType kind() const = 0;
 
-  // Returns 'true' if the buffer appears to be a valid executable of the
-  // expected type. It is not required that this be called before Disassemble.
+  // Returns true if the buffer appears to be a valid executable of the expected
+  // type, and false otherwise. This needs not be called before Disassemble().
   virtual bool ParseHeader() = 0;
 
   // Disassembles the item passed to the factory method into the output
   // parameter 'program'.
   virtual bool Disassemble(AssemblyProgram* program) = 0;
 
-  // Returns the length of the source executable. May reduce after ParseHeader.
+  // ok() may always be called but returns true only after ParseHeader()
+  // succeeds.
+  bool ok() const { return failure_reason_ == nullptr; }
+
+  // Returns the length of the image. May reduce after ParseHeader().
   size_t length() const { return length_; }
   const uint8_t* start() const { return start_; }
   const uint8_t* end() const { return end_; }
 
-  // Returns a pointer into the memory copy of the file format.
-  // FileOffsetToPointer(0) returns a pointer to the start of the file format.
-  const uint8_t* OffsetToPointer(size_t offset) const;
-
  protected:
   Disassembler(const void* start, size_t length);
 
@@ -55,16 +57,16 @@ class Disassembler {
   }
 
   // Reduce the length of the image in memory. Does not actually free
-  // (or realloc) any memory. Usually only called via ParseHeader()
+  // (or realloc) any memory. Usually only called via ParseHeader().
   void ReduceLength(size_t reduced_length);
 
  private:
   const char* failure_reason_;
 
   //
-  // Basic information that is always valid after Construction, though
-  // ParseHeader may shorten the length if the executable is shorter than
-  // the total data.
+  // Basic information that is always valid after construction, although
+  // ParseHeader() may shorten |length_| if the executable is shorter than the
+  // total data.
   //
   size_t length_;         // In current memory.
   const uint8_t* start_;  // In current memory, base for 'file offsets'.