Logical processors & page size potential bugs

General JUCE discussion
1

Hi,

There is a potential bug detecting the number of logical processors and page size in Win.
A 32 bit app running under WOW64 must use GetNativeSystemInfo(…).

So the function CPUFlags() (in juce_win32_SystemStats.cpp)

SystemStats::CPUFlags::CPUFlags()
{
    hasMMX   = IsProcessorFeaturePresent (PF_MMX_INSTRUCTIONS_AVAILABLE) != 0;
    hasSSE   = IsProcessorFeaturePresent (PF_XMMI_INSTRUCTIONS_AVAILABLE) != 0;
    hasSSE2  = IsProcessorFeaturePresent (PF_XMMI64_INSTRUCTIONS_AVAILABLE) != 0;
   #ifdef PF_AMD3D_INSTRUCTIONS_AVAILABLE
    has3DNow = IsProcessorFeaturePresent (PF_AMD3D_INSTRUCTIONS_AVAILABLE) != 0;
   #else
    has3DNow = IsProcessorFeaturePresent (PF_3DNOW_INSTRUCTIONS_AVAILABLE) != 0;
   #endif

    SYSTEM_INFO systemInfo;
    GetSystemInfo (&systemInfo);
    numCpus = (int) systemInfo.dwNumberOfProcessors; 
}

should be:

SystemStats::CPUFlags::CPUFlags()
{
    hasMMX   = IsProcessorFeaturePresent (PF_MMX_INSTRUCTIONS_AVAILABLE) != 0;
    hasSSE   = IsProcessorFeaturePresent (PF_XMMI_INSTRUCTIONS_AVAILABLE) != 0;
    hasSSE2  = IsProcessorFeaturePresent (PF_XMMI64_INSTRUCTIONS_AVAILABLE) != 0;
   #ifdef PF_AMD3D_INSTRUCTIONS_AVAILABLE
    has3DNow = IsProcessorFeaturePresent (PF_AMD3D_INSTRUCTIONS_AVAILABLE) != 0;
   #else
    has3DNow = IsProcessorFeaturePresent (PF_3DNOW_INSTRUCTIONS_AVAILABLE) != 0;
   #endif

    SYSTEM_INFO systemInfo;
    BOOL isWow64 = FALSE; 
    typedef BOOL(WINAPI* LPFN_ISWOW64PROCESS)(HANDLE, PBOOL); 
    LPFN_ISWOW64PROCESS fnIsWow64Process = (LPFN_ISWOW64PROCESS)GetProcAddress(GetModuleHandle(_T("kernel32")), "IsWow64Process"); 
    if(fnIsWow64Process && fnIsWow64Process(GetCurrentProcess(), &isWow64) && isWow64) 
    { 
      // This is a 32 bit app running under WOW64 
      GetNativeSystemInfo(&systemInfo);
    } 
    else 
    { 
      GetSystemInfo(&systemInfo);
    } 
    numCpus = (int)systemInfo.dwNumberOfProcessors; 
}

And the function SystemStats::getPageSize() should also use GetNativeSystemInfo(…) with 32 bit apps under WOW64.

2

Ok… Although looking at the docs for GetNativeSystemInfo(), I can’t really see any reason why I shouldn’t just use it to replace all the calls to GetSystemInfo? Or am I misunderstanding…?

3

MSDN::GetSystemInfo: “To retrieve accurate information for an application running on WOW64, call the GetNativeSystemInfo function.”
Of course this change is only necessary for 32 bit apps running under 64 bits (WOW64).

4

Yeah, but that says that it works for wow64 - it doesn’t say that it ONLY works on wow64!

It sounds like it’ll work on any system that’s XP or later, so I can’t think of a reason not to just use it everywhere instead of GetSystemInfo…?

5

[quote=“jules”]Yeah, but that says that it works for wow64 - it doesn’t say that it ONLY works on wow64!

It sounds like it’ll work on any system that’s XP or later, so I can’t think of a reason not to just use it everywhere instead of GetSystemInfo…?[/quote]

The MSDN isn’t clear about this, I’ll check if GetNativeSystemInfo works correctly under 32 bits OS.

6

[quote=“Xavi”][quote=“jules”]Yeah, but that says that it works for wow64 - it doesn’t say that it ONLY works on wow64!

It sounds like it’ll work on any system that’s XP or later, so I can’t think of a reason not to just use it everywhere instead of GetSystemInfo…?[/quote]

The MSDN isn’t clear about this, I’ll check if GetNativeSystemInfo works correctly under 32 bits OS.[/quote]

Yes, I’ve tested it under XP SP3 (32 bits) and both functions return identical structs so I think it’s safe to replace GetSystemInfo by GetNativeSystemInfo.

7

Thanks, will do!