Bug 1345939 - Protect TimeStamp::Now() from going backwards on hardware with... (e5332cb3) · Commits · Tommy Webb / Tor Browser

mozglue/misc/TimeStamp_windows.cpp

+18 −2

Original line number	Diff line number	Diff line
		@@ -197,6 +197,18 @@ PerformanceCounter()
		{
		LARGE_INTEGER pc;
		::QueryPerformanceCounter(&pc);

		if (!sHasStableTSC) {
		// This is a simple go-backward protection for faulty hardware
		AutoCriticalSection lock(&sTimeStampLock);

		static decltype(LARGE_INTEGER::QuadPart) last;
		if (last > pc.QuadPart) {
		return last * 1000ULL;
		}
		last = pc.QuadPart;
		}

		return pc.QuadPart * 1000ULL;
		}

		@@ -452,10 +464,12 @@ HasStableTSC()
		} cpuInfo;

		__cpuid(cpuInfo.regs, 0);
		// Only allow Intel CPUs for now
		// Only allow Intel or AMD CPUs for now.
		// The order of the registers is reg[1], reg[3], reg[2]. We just adjust the
		// string so that we can compare in one go.
		if (_strnicmp(cpuInfo.cpuString, "GenuntelineI",
		sizeof(cpuInfo.cpuString)) &&
		_strnicmp(cpuInfo.cpuString, "AuthcAMDenti",
		sizeof(cpuInfo.cpuString))) {
		return false;
		}
		@@ -465,12 +479,14 @@ HasStableTSC()
		// detect if the Advanced Power Management feature is supported
		__cpuid(regs, 0x80000000);
		if (regs[0] < 0x80000007) {
		// XXX should we return true here? If there is no APM there may be
		// no way how TSC can run out of sync among cores.
		return false;
		}

		__cpuid(regs, 0x80000007);
		// if bit 8 is set than TSC will run at a constant rate
		// in all ACPI P-state, C-states and T-states
		// in all ACPI P-states, C-states and T-states
		return regs[3] & (1 << 8);
		}