Function OverrideFunctionWithHotPatch

runtime/interception/interception_win.cpp:769–817

}

bool OverrideFunctionWithHotPatch(
    uptr old_func, uptr new_func, uptr *orig_old_func) {
  const int kHotPatchHeaderLen = kBranchLength;

  uptr header = (uptr)old_func - kHotPatchHeaderLen;
  uptr patch_length = kHotPatchHeaderLen + kShortJumpInstructionLength;

  // Validate that the function is hot patchable.
  size_t instruction_size = GetInstructionSize(old_func);
  if (instruction_size < kShortJumpInstructionLength ||
      !FunctionHasPadding(old_func, kHotPatchHeaderLen))
    return false;

  if (orig_old_func) {
    // Put the needed instructions into the trampoline bytes.
    uptr trampoline_length = instruction_size + kDirectBranchLength;
    uptr trampoline = AllocateMemoryForTrampoline(old_func, trampoline_length);
    if (!trampoline)
      return false;
    if (!CopyInstructions(trampoline, old_func, instruction_size))
      return false;
    WriteDirectBranch(trampoline + instruction_size,
                      old_func + instruction_size);
    *orig_old_func = trampoline;
  }

  // If needed, get memory space for indirect address.
  uptr indirect_address = 0;
#if SANITIZER_WINDOWS64
  indirect_address = AllocateMemoryForTrampoline(old_func, kAddressLength);
  if (!indirect_address)
    return false;
#endif

  // Change memory protection to writable.
  DWORD protection = 0;
  if (!ChangeMemoryProtection(header, patch_length, &protection))
    return false;

  // Write jumps to the redirected function.
  WriteBranch(header, indirect_address, new_func);
  WriteShortJumpInstruction(old_func, header);

  // Restore previous memory protection.
  if (!RestoreMemoryProtection(header, patch_length, protection))
    return false;

  return true;
}

bool OverrideFunctionWithTrampoline(
    uptr old_func, uptr new_func, uptr *orig_old_func) {