tor-browser

The Tor Browser
git clone https://git.dasho.dev/tor-browser.git
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WindowsDiagnostics.cpp (2825B)

      1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
      2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
      3 /* This Source Code Form is subject to the terms of the Mozilla Public
      4 * License, v. 2.0. If a copy of the MPL was not distributed with this
      5 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
      6 
      7 #include "mozilla/WindowsDiagnostics.h"
      8 
      9 #include "mozilla/Assertions.h"
     10 #include "mozilla/Attributes.h"
     11 #include "mozilla/Types.h"
     12 
     13 #include <windows.h>
     14 #include <winternl.h>
     15 
     16 #if defined(_M_AMD64)
     17 
     18 namespace mozilla {
     19 
     20 MOZ_RUNINIT static OnSingleStepCallback sOnSingleStepCallback{};
     21 static void* sOnSingleStepCallbackState = nullptr;
     22 static bool sIsSingleStepping = false;
     23 
     24 MFBT_API AutoOnSingleStepCallback::AutoOnSingleStepCallback(
     25    OnSingleStepCallback aOnSingleStepCallback, void* aState) {
     26  MOZ_RELEASE_ASSERT(!sIsSingleStepping && !sOnSingleStepCallback &&
     27                         !sOnSingleStepCallbackState,
     28                     "Single-stepping is already active");
     29 
     30  sOnSingleStepCallback = std::move(aOnSingleStepCallback);
     31  sOnSingleStepCallbackState = aState;
     32  sIsSingleStepping = true;
     33 }
     34 
     35 MFBT_API AutoOnSingleStepCallback::~AutoOnSingleStepCallback() {
     36  sOnSingleStepCallback = OnSingleStepCallback();
     37  sOnSingleStepCallbackState = nullptr;
     38  sIsSingleStepping = false;
     39 }
     40 
     41 // Going though this assembly code turns on the trap flag, which will trigger
     42 // a first single-step exception. It is then up to the exception handler to
     43 // keep the trap flag enabled so that a new single step exception gets
     44 // triggered with the following instruction.
     45 MFBT_API MOZ_NEVER_INLINE MOZ_NAKED void EnableTrapFlag() {
     46  asm volatile(
     47      "pushfq;"
     48      "orw $0x100,(%rsp);"
     49      "popfq;"
     50      "retq;");
     51 }
     52 
     53 // This function does not do anything special, but when we reach its address
     54 // while single-stepping the exception handler will know that it is now time to
     55 // leave the trap flag turned off.
     56 MFBT_API MOZ_NEVER_INLINE MOZ_NAKED void DisableTrapFlag() {
     57  asm volatile("retq;");
     58 }
     59 
     60 MFBT_API LONG SingleStepExceptionHandler(_EXCEPTION_POINTERS* aExceptionInfo) {
     61  if (sIsSingleStepping && sOnSingleStepCallback &&
     62      aExceptionInfo->ExceptionRecord->ExceptionCode == EXCEPTION_SINGLE_STEP) {
     63    auto instructionPointer = aExceptionInfo->ContextRecord->Rip;
     64    bool keepOnSingleStepping = false;
     65    if (instructionPointer != reinterpret_cast<uintptr_t>(&DisableTrapFlag)) {
     66      keepOnSingleStepping = sOnSingleStepCallback(
     67          sOnSingleStepCallbackState, aExceptionInfo->ContextRecord);
     68    }
     69    if (keepOnSingleStepping) {
     70      aExceptionInfo->ContextRecord->EFlags |= 0x100;
     71    } else {
     72      sIsSingleStepping = false;
     73    }
     74    return EXCEPTION_CONTINUE_EXECUTION;
     75  }
     76  return EXCEPTION_CONTINUE_SEARCH;
     77 }
     78 
     79 }  // namespace mozilla
     80 
     81 #endif  // _M_AMD64