[Courgette] Simple AssemblyProgram and Disassembler cleanups.

courgette/disassembler_elf_32.h

Index: courgette/disassembler_elf_32.h
diff --git a/courgette/disassembler_elf_32.h b/courgette/disassembler_elf_32.h
index 395f571e0bf1929ad76584c5f31e94dd64114111..3cf42e2e546107433cf7d4d9c411fe7bd7ed7b9f 100644
--- a/courgette/disassembler_elf_32.h
+++ b/courgette/disassembler_elf_32.h
@@ -104,8 +104,9 @@ class DisassemblerElf32 : public Disassembler {
   FileOffset RVAToFileOffset(RVA rva) const override;
   RVA PointerToTargetRVA(const uint8_t* p) const override;
   ExecutableType kind() const override = 0;
+  uint64_t image_base() const override { return 0; }

[Will Harris, 2017/01/11 21:15:35]

why have the image_base in the elf disassembler at all...? Does this just make
the assembly_program code simpler? It seems strange to return 0

[huangs, 2017/01/12 19:54:42]

I'd rather keep as is for now for this CL. Reason:

In Courgette, data are passed via injection by:

  Disassembler --> AssemblyProgram --> EncodedProgram

where data receiver does not "know" about sender. Now, |image_base| is used by
(1) Win32 Disassembler, (2) EncodedProgram.  Right now |image_base| is passed
from Disassembler to EncodedProgram by using AssemblyProgram as middleman. 
Unfavorable alternatives are:
- Requiring both Disassembler & AssemblyProgram to instantiate EncodedProgram.
- Pass |image_base| via "side band" when intantiating EncodedProgram; this leaks
abstraction for callers.

A potential alternative is to have Disassembler inject |image_base| directly to
EncodedProgram, also as a part of AssemblyProgram reduction. This is beyond the
scope of this CL, which is just simple cleanup.

[Will Harris, 2017/01/12 19:55:55]

Acknowledged.

[huangs, 2017/01/13 16:44:54]

Acknowledged.

   bool ParseHeader() override;
-  bool Disassemble(AssemblyProgram* target) override;
+  bool Disassemble(AssemblyProgram* program) override;
 
   virtual e_machine_values ElfEM() const = 0;