Experiment for updating the tcmalloc chromium branch to r144 (gperftools 2.0).

third_party/tcmalloc/chromium/src/windows/preamble_patcher.cc

Index: third_party/tcmalloc/chromium/src/windows/preamble_patcher.cc
diff --git a/third_party/tcmalloc/chromium/src/windows/preamble_patcher.cc b/third_party/tcmalloc/chromium/src/windows/preamble_patcher.cc
index 78a47639feee0c6066323eccda4bd18b3e100f38..b27a95bcb6f737f16d32e74c8243bb31c6810668 100644
--- a/third_party/tcmalloc/chromium/src/windows/preamble_patcher.cc
+++ b/third_party/tcmalloc/chromium/src/windows/preamble_patcher.cc
@@ -29,6 +29,7 @@
  *
  * ---
  * Author: Joi Sigurdsson
+ * Author: Scott Francis
  *
  * Implementation of PreamblePatcher
  */
@@ -46,18 +47,42 @@
 #define ASM_JMP32ABS_0 0xFF
 #define ASM_JMP32ABS_1 0x25
 #define ASM_JMP8REL 0xEB
+#define ASM_JCC32REL_0 0x0F
+#define ASM_JCC32REL_1_MASK 0x80
+#define ASM_NOP 0x90
+// X64 opcodes
+#define ASM_REXW 0x48
+#define ASM_MOVRAX_IMM 0xB8
+#define ASM_JMP 0xFF
+#define ASM_JMP_RAX 0xE0
 
 namespace sidestep {
 
+PreamblePatcher::PreamblePage* PreamblePatcher::preamble_pages_ = NULL;
+long PreamblePatcher::granularity_ = 0;
+long PreamblePatcher::pagesize_ = 0;
+bool PreamblePatcher::initialized_ = false;
+
+static const unsigned int kPreamblePageMagic = 0x4347414D; // "MAGC"
+
 // Handle a special case that we see with functions that point into an
 // IAT table (including functions linked statically into the
 // application): these function already starts with ASM_JMP32*.  For
 // instance, malloc() might be implemented as a JMP to __malloc().
 // This function follows the initial JMPs for us, until we get to the
 // place where the actual code is defined.  If we get to STOP_BEFORE,
-// we return the address before stop_before.
+// we return the address before stop_before.  The stop_before_trampoline
+// flag is used in 64-bit mode.  If true, we will return the address
+// before a trampoline is detected.  Trampolines are defined as:
+//
+//    nop
+//    mov rax, <replacement_function>
+//    jmp rax
+//
+// See PreamblePatcher::RawPatchWithStub for more information.
 void* PreamblePatcher::ResolveTargetImpl(unsigned char* target,
-                                         unsigned char* stop_before) {
+                                         unsigned char* stop_before,
+                                         bool stop_before_trampoline) {
   if (target == NULL)
     return NULL;
   while (1) {
@@ -81,15 +106,26 @@ void* PreamblePatcher::ResolveTargetImpl(unsigned char* target,
       // Visual studio seems to sometimes do it this way instead of the
       // previous way.  Not sure what the rules are, but it was happening
       // with operator new in some binaries.
-      void **new_target_v;
-      SIDESTEP_ASSERT(sizeof(new_target) == 4);
-      memcpy(&new_target_v, reinterpret_cast<void*>(target + 2), 4);
+      void** new_target_v;
+      if (kIs64BitBinary) {
+        // In 64-bit mode JMPs are RIP-relative, not absolute
+        int target_offset;
+        memcpy(reinterpret_cast<void*>(&target_offset),
+               reinterpret_cast<void*>(target + 2), 4);
+        new_target_v = reinterpret_cast<void**>(target + target_offset + 6);
+      } else {
+        SIDESTEP_ASSERT(sizeof(new_target) == 4);
+        memcpy(&new_target_v, reinterpret_cast<void*>(target + 2), 4);
+      }
       new_target = reinterpret_cast<unsigned char*>(*new_target_v);
     } else {
       break;
     }
     if (new_target == stop_before)
       break;
+    if (stop_before_trampoline && *new_target == ASM_NOP
+        && new_target[1] == ASM_REXW && new_target[2] == ASM_MOVRAX_IMM)
+      break;
     target = new_target;
   }
   return target;
@@ -103,7 +139,7 @@ class DeleteUnsignedCharArray {
 
   ~DeleteUnsignedCharArray() {
     if (array_) {
-      delete [] array_;
+      PreamblePatcher::FreePreambleBlock(array_);
     }
   }
 
@@ -191,9 +227,23 @@ SideStepError PreamblePatcher::RawPatch(void* target_function,
     return SIDESTEP_INVALID_PARAMETER;
   }
 
-  // @see MAX_PREAMBLE_STUB_SIZE for an explanation of how we arrives at
-  // this size
-  unsigned char* preamble_stub = new unsigned char[MAX_PREAMBLE_STUB_SIZE];
+  BOOL succeeded = FALSE;
+
+  // First, deal with a special case that we see with functions that
+  // point into an IAT table (including functions linked statically
+  // into the application): these function already starts with
+  // ASM_JMP32REL.  For instance, malloc() might be implemented as a
+  // JMP to __malloc().  In that case, we replace the destination of
+  // the JMP (__malloc), rather than the JMP itself (malloc).  This
+  // way we get the correct behavior no matter how malloc gets called.
+  void* new_target = ResolveTarget(target_function);
+  if (new_target != target_function) {
+    target_function = new_target;
+  }
+
+  // In 64-bit mode, preamble_stub must be within 2GB of target function
+  // so that if target contains a jump, we can translate it.
+  unsigned char* preamble_stub = AllocPreambleBlockNear(target_function);
   if (!preamble_stub) {
     SIDESTEP_ASSERT(false && "Unable to allocate preamble-stub.");
     return SIDESTEP_INSUFFICIENT_BUFFER;
@@ -202,19 +252,6 @@ SideStepError PreamblePatcher::RawPatch(void* target_function,
   // Frees the array at end of scope.
   DeleteUnsignedCharArray guard_preamble_stub(preamble_stub);
 
-  // Change the protection of the newly allocated preamble stub to
-  // PAGE_EXECUTE_READWRITE. This is required to work with DEP (Data
-  // Execution Prevention) which will cause an exception if code is executed
-  // from a page on which you do not have read access.
-  DWORD old_stub_protect = 0;
-  BOOL succeeded = ::VirtualProtect(preamble_stub, MAX_PREAMBLE_STUB_SIZE,
-                                    PAGE_EXECUTE_READWRITE, &old_stub_protect);
-  if (!succeeded) {
-    SIDESTEP_ASSERT(false &&
-                    "Failed to make page preamble stub read-write-execute.");
-    return SIDESTEP_ACCESS_DENIED;
-  }
-
   SideStepError error_code = RawPatchWithStubAndProtections(
       target_function, replacement_function, preamble_stub,
       MAX_PREAMBLE_STUB_SIZE, NULL);
@@ -260,23 +297,6 @@ SideStepError PreamblePatcher::Unpatch(void* target_function,
     return SIDESTEP_INVALID_PARAMETER;
   }
 
-  // We disassemble the preamble of the _stub_ to see how many bytes we
-  // originally copied to the stub.
-  MiniDisassembler disassembler;
-  unsigned int preamble_bytes = 0;
-  while (preamble_bytes < 5) {
-    InstructionType instruction_type =
-        disassembler.Disassemble(
-            reinterpret_cast<unsigned char*>(original_function_stub) +
-            preamble_bytes,
-            preamble_bytes);
-    if (IT_GENERIC != instruction_type) {
-      SIDESTEP_ASSERT(false &&
-                      "Should only have generic instructions in stub!!");
-      return SIDESTEP_UNSUPPORTED_INSTRUCTION;
-    }
-  }
-
   // Before unpatching, target_function should be a JMP to
   // replacement_function.  If it's not, then either it's an error, or
   // we're falling into the case where the original instruction was a
@@ -286,7 +306,8 @@ SideStepError PreamblePatcher::Unpatch(void* target_function,
   unsigned char* target = reinterpret_cast<unsigned char*>(target_function);
   target = reinterpret_cast<unsigned char*>(
       ResolveTargetImpl(
-          target, reinterpret_cast<unsigned char*>(replacement_function)));
+          target, reinterpret_cast<unsigned char*>(replacement_function),
+          true));
   // We should end at the function we patched.  When we patch, we insert
   // a ASM_JMP32REL instruction, so look for that as a sanity check.
   if (target[0] != ASM_JMP32REL) {
@@ -295,11 +316,13 @@ SideStepError PreamblePatcher::Unpatch(void* target_function,
     return SIDESTEP_INVALID_PARAMETER;
   }
 
+  const unsigned int kRequiredTargetPatchBytes = 5;
+
   // We need to be able to write to a process-local copy of the first
-  // MAX_PREAMBLE_STUB_SIZE bytes of target_function
+  // kRequiredTargetPatchBytes bytes of target_function
   DWORD old_target_function_protect = 0;
-  BOOL succeeded = ::VirtualProtect(reinterpret_cast<void*>(target_function),
-                                    MAX_PREAMBLE_STUB_SIZE,
+  BOOL succeeded = ::VirtualProtect(reinterpret_cast<void*>(target),
+                                    kRequiredTargetPatchBytes,
                                     PAGE_EXECUTE_READWRITE,
                                     &old_target_function_protect);
   if (!succeeded) {
@@ -308,20 +331,67 @@ SideStepError PreamblePatcher::Unpatch(void* target_function,
     return SIDESTEP_ACCESS_DENIED;
   }
 
-  // Replace the first few bytes of the original function with the bytes we
-  // previously moved to the preamble stub.
-  memcpy(reinterpret_cast<void*>(target),
-         original_function_stub, preamble_bytes);
+  unsigned char* preamble_stub = reinterpret_cast<unsigned char*>(
+                                   original_function_stub);
 
-  // Stub is now useless so delete it.
-  // [csilvers: Commented out for perftools because it causes big problems
-  //  when we're unpatching malloc.  We just let this live on as a  leak.]
-  //delete [] reinterpret_cast<unsigned char*>(original_function_stub);
+  // Disassemble the preamble of stub and copy the bytes back to target.
+  // If we've done any conditional jumps in the preamble we need to convert
+  // them back to the orignal REL8 jumps in the target.
+  MiniDisassembler disassembler;
+  unsigned int preamble_bytes = 0;
+  unsigned int target_bytes = 0;
+  while (target_bytes < kRequiredTargetPatchBytes) {
+    unsigned int cur_bytes = 0;
+    InstructionType instruction_type =
+        disassembler.Disassemble(preamble_stub + preamble_bytes, cur_bytes);
+    if (IT_JUMP == instruction_type) {
+      unsigned int jump_bytes = 0;
+      SideStepError jump_ret = SIDESTEP_JUMP_INSTRUCTION;
+      if (IsNearConditionalJump(preamble_stub + preamble_bytes, cur_bytes) ||
+          IsNearRelativeJump(preamble_stub + preamble_bytes, cur_bytes) ||
+          IsNearAbsoluteCall(preamble_stub + preamble_bytes, cur_bytes) ||
+          IsNearRelativeCall(preamble_stub + preamble_bytes, cur_bytes)) {
+        jump_ret = PatchNearJumpOrCall(preamble_stub + preamble_bytes, 
+                                       cur_bytes, target + target_bytes, 
+                                       &jump_bytes, MAX_PREAMBLE_STUB_SIZE);
+      }
+      if (jump_ret == SIDESTEP_JUMP_INSTRUCTION) {
+        SIDESTEP_ASSERT(false &&
+                        "Found unsupported jump instruction in stub!!");
+        return SIDESTEP_UNSUPPORTED_INSTRUCTION;
+      }
+      target_bytes += jump_bytes;
+    } else if (IT_GENERIC == instruction_type) {
+      if (IsMovWithDisplacement(preamble_stub + preamble_bytes, cur_bytes)) {
+        unsigned int mov_bytes = 0;
+        if (PatchMovWithDisplacement(preamble_stub + preamble_bytes, cur_bytes,
+                                     target + target_bytes, &mov_bytes,
+                                     MAX_PREAMBLE_STUB_SIZE)
+                                     != SIDESTEP_SUCCESS) {
+          SIDESTEP_ASSERT(false &&
+                          "Found unsupported generic instruction in stub!!");
+          return SIDESTEP_UNSUPPORTED_INSTRUCTION;
+        }
+      } else {
+        memcpy(reinterpret_cast<void*>(target + target_bytes),
+               reinterpret_cast<void*>(reinterpret_cast<unsigned char*>(
+                   original_function_stub) + preamble_bytes), cur_bytes);
+        target_bytes += cur_bytes;
+      }
+    } else {
+      SIDESTEP_ASSERT(false &&
+                      "Found unsupported instruction in stub!!");
+      return SIDESTEP_UNSUPPORTED_INSTRUCTION;
+    }
+    preamble_bytes += cur_bytes;
+  }
 
-  // Restore the protection of the first MAX_PREAMBLE_STUB_SIZE bytes of
+  FreePreambleBlock(reinterpret_cast<unsigned char*>(original_function_stub));
+
+  // Restore the protection of the first kRequiredTargetPatchBytes bytes of
   // target to what they were before we started goofing around.
   succeeded = ::VirtualProtect(reinterpret_cast<void*>(target),
-                               MAX_PREAMBLE_STUB_SIZE,
+                               kRequiredTargetPatchBytes,
                                old_target_function_protect,
                                &old_target_function_protect);
 
@@ -341,4 +411,274 @@ SideStepError PreamblePatcher::Unpatch(void* target_function,
   return SIDESTEP_SUCCESS;
 }
 
+void PreamblePatcher::Initialize() {
+  if (!initialized_) {
+    SYSTEM_INFO si = { 0 };
+    ::GetSystemInfo(&si);
+    granularity_ = si.dwAllocationGranularity;
+    pagesize_ = si.dwPageSize;
+    initialized_ = true;
+  }
+}
+
+unsigned char* PreamblePatcher::AllocPreambleBlockNear(void* target) {
+  PreamblePage* preamble_page = preamble_pages_;
+  while (preamble_page != NULL) {
+    if (preamble_page->free_ != NULL) {
+      __int64 val = reinterpret_cast<__int64>(preamble_page) -
+          reinterpret_cast<__int64>(target);
+      if ((val > 0 && val + pagesize_ <= INT_MAX) ||
+          (val < 0 && val >= INT_MIN)) {
+        break;
+      }
+    }
+    preamble_page = preamble_page->next_;
+  }
+
+  // The free_ member of the page is used to store the next available block
+  // of memory to use or NULL if there are no chunks available, in which case
+  // we'll allocate a new page.
+  if (preamble_page == NULL || preamble_page->free_ == NULL) {
+    // Create a new preamble page and initialize the free list
+    preamble_page = reinterpret_cast<PreamblePage*>(AllocPageNear(target));
+    SIDESTEP_ASSERT(preamble_page != NULL && "Could not allocate page!");
+    void** pp = &preamble_page->free_;
+    unsigned char* ptr = reinterpret_cast<unsigned char*>(preamble_page) +
+        MAX_PREAMBLE_STUB_SIZE;
+    unsigned char* limit = reinterpret_cast<unsigned char*>(preamble_page) +
+        pagesize_;
+    while (ptr < limit) {
+      *pp = ptr;
+      pp = reinterpret_cast<void**>(ptr);
+      ptr += MAX_PREAMBLE_STUB_SIZE;
+    }
+    *pp = NULL;
+    // Insert the new page into the list
+    preamble_page->magic_ = kPreamblePageMagic;
+    preamble_page->next_ = preamble_pages_;
+    preamble_pages_ = preamble_page;
+  }
+  unsigned char* ret = reinterpret_cast<unsigned char*>(preamble_page->free_);
+  preamble_page->free_ = *(reinterpret_cast<void**>(preamble_page->free_));
+  return ret;
+}
+
+void PreamblePatcher::FreePreambleBlock(unsigned char* block) {
+  SIDESTEP_ASSERT(block != NULL);
+  SIDESTEP_ASSERT(granularity_ != 0);
+  uintptr_t ptr = reinterpret_cast<uintptr_t>(block);
+  ptr -= ptr & (granularity_ - 1);
+  PreamblePage* preamble_page = reinterpret_cast<PreamblePage*>(ptr);
+  SIDESTEP_ASSERT(preamble_page->magic_ == kPreamblePageMagic);
+  *(reinterpret_cast<void**>(block)) = preamble_page->free_;
+  preamble_page->free_ = block;
+}
+
+void* PreamblePatcher::AllocPageNear(void* target) {
+  MEMORY_BASIC_INFORMATION mbi = { 0 };
+  if (!::VirtualQuery(target, &mbi, sizeof(mbi))) {
+    SIDESTEP_ASSERT(false && "VirtualQuery failed on target address");
+    return 0;
+  }
+  if (initialized_ == false) {
+    PreamblePatcher::Initialize();
+    SIDESTEP_ASSERT(initialized_);
+  }
+  void* pv = NULL;
+  unsigned char* allocation_base = reinterpret_cast<unsigned char*>(
+      mbi.AllocationBase);
+  __int64 i = 1;
+  bool high_target = reinterpret_cast<__int64>(target) > UINT_MAX;
+  while (pv == NULL) {
+    __int64 val = reinterpret_cast<__int64>(allocation_base) -
+        (i * granularity_);
+    if (high_target &&
+        reinterpret_cast<__int64>(target) - val > INT_MAX) {
+        // We're further than 2GB from the target
+      break;
+    } else if (val <= NULL) {
+      // Less than 0
+      break;
+    }
+    pv = ::VirtualAlloc(reinterpret_cast<void*>(allocation_base -
+                            (i++ * granularity_)),
+                        pagesize_, MEM_COMMIT | MEM_RESERVE,
+                        PAGE_EXECUTE_READWRITE);
+  }
+
+  // We couldn't allocate low, try to allocate high
+  if (pv == NULL) {
+    i = 1;
+    // Round up to the next multiple of page granularity
+    allocation_base = reinterpret_cast<unsigned char*>(
+        (reinterpret_cast<__int64>(target) &
+        (~(granularity_ - 1))) + granularity_);
+    while (pv == NULL) {
+      __int64 val = reinterpret_cast<__int64>(allocation_base) +
+          (i * granularity_) - reinterpret_cast<__int64>(target);
+      if (val > INT_MAX || val < 0) {
+        // We're too far or we overflowed
+        break;
+      }
+      pv = ::VirtualAlloc(reinterpret_cast<void*>(allocation_base +
+                              (i++ * granularity_)),
+                          pagesize_, MEM_COMMIT | MEM_RESERVE,
+                          PAGE_EXECUTE_READWRITE);
+    }
+  }
+  return pv;
+}
+
+bool PreamblePatcher::IsShortConditionalJump(
+    unsigned char* target,
+    unsigned int instruction_size) {
+  return (*(target) & 0x70) == 0x70 && instruction_size == 2;
+}
+
+bool PreamblePatcher::IsNearConditionalJump(
+    unsigned char* target,
+    unsigned int instruction_size) {
+  return *(target) == 0xf && (*(target + 1) & 0x80) == 0x80 &&
+      instruction_size == 6;
+}
+
+bool PreamblePatcher::IsNearRelativeJump(
+    unsigned char* target,
+    unsigned int instruction_size) {
+  return *(target) == 0xe9 && instruction_size == 5;
+}
+
+bool PreamblePatcher::IsNearAbsoluteCall(
+    unsigned char* target,
+    unsigned int instruction_size) {
+  return *(target) == 0xff && (*(target + 1) & 0x10) == 0x10 &&
+      instruction_size == 6;
+}
+
+bool PreamblePatcher::IsNearRelativeCall(
+    unsigned char* target,
+    unsigned int instruction_size) {
+  return *(target) == 0xe8 && instruction_size == 5;
+}
+
+bool PreamblePatcher::IsMovWithDisplacement(
+    unsigned char* target,
+    unsigned int instruction_size) {
+  // In this case, the ModRM byte's mod field will be 0 and r/m will be 101b (5)
+  return instruction_size == 7 && *target == 0x48 && *(target + 1) == 0x8b &&
+      (*(target + 2) >> 6) == 0 && (*(target + 2) & 0x7) == 5;
+}
+
+SideStepError PreamblePatcher::PatchShortConditionalJump(
+    unsigned char* source,
+    unsigned int instruction_size,
+    unsigned char* target,
+    unsigned int* target_bytes,
+    unsigned int target_size) {
+  unsigned char* original_jump_dest = (source + 2) + source[1];
+  unsigned char* stub_jump_from = target + 6;
+  __int64 fixup_jump_offset = original_jump_dest - stub_jump_from;
+  if (fixup_jump_offset > INT_MAX || fixup_jump_offset < INT_MIN) {
+    SIDESTEP_ASSERT(false &&
+                    "Unable to fix up short jump because target"
+                    " is too far away.");
+    return SIDESTEP_JUMP_INSTRUCTION;
+  }
+
+  *target_bytes = 6;
+  if (target_size > *target_bytes) {
+    // Convert the short jump to a near jump.
+    //
+    // 0f 8x xx xx xx xx = Jcc rel32off
+    unsigned short jmpcode = ((0x80 | (source[0] & 0xf)) << 8) | 0x0f;
+    memcpy(reinterpret_cast<void*>(target),
+           reinterpret_cast<void*>(&jmpcode), 2);
+    memcpy(reinterpret_cast<void*>(target + 2),
+           reinterpret_cast<void*>(&fixup_jump_offset), 4);
+  }
+
+  return SIDESTEP_SUCCESS;
+}
+
+SideStepError PreamblePatcher::PatchNearJumpOrCall(
+    unsigned char* source,
+    unsigned int instruction_size,
+    unsigned char* target,
+    unsigned int* target_bytes,
+    unsigned int target_size) {
+  SIDESTEP_ASSERT(instruction_size == 5 || instruction_size == 6);
+  unsigned int jmp_offset_in_instruction = instruction_size == 5 ? 1 : 2;
+  unsigned char* original_jump_dest = reinterpret_cast<unsigned char *>(
+      reinterpret_cast<__int64>(source + instruction_size) +
+      *(reinterpret_cast<int*>(source + jmp_offset_in_instruction)));
+  unsigned char* stub_jump_from = target + instruction_size;
+  __int64 fixup_jump_offset = original_jump_dest - stub_jump_from;
+  if (fixup_jump_offset > INT_MAX || fixup_jump_offset < INT_MIN) {
+    SIDESTEP_ASSERT(false &&
+                    "Unable to fix up near jump because target"
+                    " is too far away.");
+    return SIDESTEP_JUMP_INSTRUCTION;
+  }
+
+  if ((fixup_jump_offset < SCHAR_MAX && fixup_jump_offset > SCHAR_MIN)) {
+    *target_bytes = 2;
+    if (target_size > *target_bytes) {
+      // If the new offset is in range, use a short jump instead of a near jump.
+      if (source[0] == ASM_JCC32REL_0 &&
+          (source[1] & ASM_JCC32REL_1_MASK) == ASM_JCC32REL_1_MASK) {
+        unsigned short jmpcode = (static_cast<unsigned char>(
+            fixup_jump_offset) << 8) | (0x70 | (source[1] & 0xf));
+        memcpy(reinterpret_cast<void*>(target),
+               reinterpret_cast<void*>(&jmpcode),
+               2);
+      } else {
+        target[0] = ASM_JMP8REL;
+        target[1] = static_cast<unsigned char>(fixup_jump_offset);
+      }
+    }
+  } else {
+    *target_bytes = instruction_size;
+    if (target_size > *target_bytes) {
+      memcpy(reinterpret_cast<void*>(target),
+             reinterpret_cast<void*>(source),
+             jmp_offset_in_instruction);
+      memcpy(reinterpret_cast<void*>(target + jmp_offset_in_instruction),
+             reinterpret_cast<void*>(&fixup_jump_offset),
+             4);
+    }
+  }
+
+  return SIDESTEP_SUCCESS;
+}
+
+SideStepError PreamblePatcher::PatchMovWithDisplacement(
+     unsigned char* source,
+     unsigned int instruction_size,
+     unsigned char* target,
+     unsigned int* target_bytes,
+     unsigned int target_size) {
+  SIDESTEP_ASSERT(instruction_size == 7);
+  const int mov_offset_in_instruction = 3; // 0x48 0x8b 0x0d <offset>
+  unsigned char* original_mov_dest = reinterpret_cast<unsigned char*>(
+      reinterpret_cast<__int64>(source + instruction_size) +
+      *(reinterpret_cast<int*>(source + mov_offset_in_instruction)));
+  unsigned char* stub_mov_from = target + instruction_size;
+  __int64 fixup_mov_offset = original_mov_dest - stub_mov_from;
+  if (fixup_mov_offset > INT_MAX || fixup_mov_offset < INT_MIN) {
+    SIDESTEP_ASSERT(false &&
+        "Unable to fix up near MOV because target is too far away.");
+    return SIDESTEP_UNEXPECTED;
+  }
+  *target_bytes = instruction_size;
+  if (target_size > *target_bytes) {
+    memcpy(reinterpret_cast<void*>(target),
+           reinterpret_cast<void*>(source),
+           mov_offset_in_instruction);
+    memcpy(reinterpret_cast<void*>(target + mov_offset_in_instruction),
+           reinterpret_cast<void*>(&fixup_mov_offset),
+           4);
+  }
+  return SIDESTEP_SUCCESS;
+}
+
 };  // namespace sidestep