[Courgette] Deprecate ARM support.

Courgette's ARM support was complex and was never used (except for
helping to prototype Zucchini's ARM flow, which is WIP). Recently the
code is also causing Fuzzer issues. Therefore we deem it better to just
remove the code.

This CL performs superficial removal of ARM code. For compatibility,
the enums

  enum ExecutableType { EXE_ELF_32_ARM = 3; }
  enum EncodedProgram::OP { MAKE_ELF_ARM_RELOCATION_TABLE = 7; }

are deprecated and commented out, without changing other values.

Bug: 1012592
Change-Id: Iad3a3c9e41470eef8ff004591e6ed42ea4315d06
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1986211
Reviewed-by: Etienne Pierre-Doray <[email protected]>
Commit-Queue: Samuel Huang <[email protected]>
Cr-Commit-Position: refs/heads/master@{#728580}

courgette/BUILD.gn

@@ -22,8 +22,6 @@ static_library("courgette_lib") {
     "disassembler.h",
     "disassembler_elf_32.cc",
     "disassembler_elf_32.h",
-    "disassembler_elf_32_arm.cc",
-    "disassembler_elf_32_arm.h",
     "disassembler_elf_32_x86.cc",
     "disassembler_elf_32_x86.h",
     "disassembler_win32.cc",

courgette/assembly_program.cc

@@ -31,7 +31,6 @@ class LabelReceptor : public InstructionReceptor {
   // InstructionReceptor:
   CheckBool EmitPeRelocs() override { return true; }
   CheckBool EmitElfRelocation() override { return true; }
-  CheckBool EmitElfARMRelocation() override { return true; }
   CheckBool EmitOrigin(RVA rva) override { return true; }
   CheckBool EmitSingleByte(uint8_t byte) override { return true; }
   CheckBool EmitMultipleBytes(const uint8_t* bytes, size_t len) override {
@@ -41,13 +40,6 @@ class LabelReceptor : public InstructionReceptor {
     rel32_vector_.push_back(label);
     return true;
   }
-  CheckBool EmitRel32ARM(uint16_t op,
-                         Label* label,
-                         const uint8_t* arm_op,
-                         uint16_t op_size) override {
-    rel32_vector_.push_back(label);
-    return true;
-  }
   CheckBool EmitAbs32(Label* label) override {
     abs32_vector_.push_back(label);
     return true;
@@ -75,18 +67,15 @@ void AssemblyProgram::PrecomputeLabels(RvaVisitor* abs32_visitor,
                                        RvaVisitor* rel32_visitor) {
   abs32_label_manager_.Read(abs32_visitor);
   rel32_label_manager_.Read(rel32_visitor);
-  TrimLabels();
+  // TrimLabels() should be called here if used. Previously this was used only
+  // for ARM binaries, but ARM support has been deprecated.
 }
 
 // Chosen empirically to give the best reduction in payload size for
 // an update from daisy_3701.98.0 to daisy_4206.0.0.
 const int AssemblyProgram::kLabelLowerLimit = 5;
 
 void AssemblyProgram::TrimLabels() {
-  // For now only trim for ARM binaries.
-  if (kind() != EXE_ELF_32_ARM)
-    return;
-
   int lower_limit = kLabelLowerLimit;
 
   VLOG(1) << "TrimLabels: threshold " << lower_limit;

courgette/courgette.h

@@ -57,7 +57,7 @@ enum ExecutableType {
   EXE_UNKNOWN = 0,
   EXE_WIN_32_X86 = 1,
   EXE_ELF_32_X86 = 2,
-  EXE_ELF_32_ARM = 3,
+  // EXE_ELF_32_ARM_DEPRECATED = 3,  // DEPRECATED.
   EXE_WIN_32_X64 = 4,
 };
 

courgette/courgette_tool.cc

@@ -135,11 +135,6 @@ bool Supported(const base::FilePath& input_file) {
       result = true;
       break;
 
-    case courgette::EXE_ELF_32_ARM:
-      format = "ELF 32 ARM";
-      result = true;
-      break;
-
     case courgette::EXE_WIN_32_X64:
       format = "Windows 64 PE";
       result = true;

courgette/description.html

@@ -41,7 +41,6 @@ <h3>Disassemble</h3>
 <ul>
 <li><p>disassembler_win32_x86.h defines the PE/COFF x86 disassembler</p></li>
 <li><p>disassembler_elf_32_x86.h defines the ELF 32-bit x86 disassembler</p></li>
-<li><p>disassembler_elf_32_arm.h defines the ELF 32-bit arm disassembler</p></li>
 </ul></li>
 <li><p>The Disassembler replaces the relocation table with a Courgette
 instruction that can regenerate the relocation table.</p></li>

courgette/description.md

@@ -46,8 +46,6 @@ Patch Generation
 
   - disassembler\_elf\_32\_x86.h defines the ELF 32-bit x86 disassembler
 
-  - disassembler\_elf\_32\_arm.h defines the ELF 32-bit arm disassembler
-
 - The Disassembler replaces the relocation table with a Courgette
   instruction that can regenerate the relocation table.