Utilisation du contexte XState

Ce document contient un exemple qui montre comment utiliser les fonctions de contexte XState pour récupérer et définir des fonctionnalités étendues sur un thread. Les exemples suivants manipulent l’état AVX (Intel Advanced Vector Extensions) qui est défini par FeatureId 2 (Feature Mask 4). Intel AVX est défini dans la « Référence de programmation des extensions vectorielles avancées Intel » disponible à partir de https://go.microsoft.com/fwlink/p/?linkid=212716.

Windows 7 avec SP1 :L’API AVX est implémentée pour la première fois sur Windows 7 avec SP1. Étant donné qu’il n’existe pas de KIT de développement logiciel (SDK) pour Windows 7 avec SP1, cela signifie qu’il n’y a pas d’en-têtes et de fichiers de bibliothèque disponibles à utiliser. Dans ce cas, un appelant doit déclarer les fonctions nécessaires à partir de cette documentation et obtenir des pointeurs vers ces fonctions à l’aide de GetModuleHandle sur « Kernel32.dll », puis des appels à GetProcAddress.

#include <stdlib.h>
#include <stdio.h>
#include <tchar.h>
#include <windows.h>
#include <winerror.h>

// Windows 7 SP1 is the first version of Windows to support the AVX API.

// The value for CONTEXT_XSTATE has changed between Windows 7 and
// Windows 7 SP1 and greater.
// While the value will be correct for future SDK headers, we need to set 
// this value manually when building with a Windows 7 SDK for running on 
// Windows 7 SPI OS bits.

#undef CONTEXT_XSTATE

#if defined(_M_X64)
#define CONTEXT_XSTATE                      (0x00100040)
#else
#define CONTEXT_XSTATE                      (0x00010040)
#endif

// Since the AVX API is not declared in the Windows 7 SDK headers and 
// since we don't have the proper libs to work with, we will declare 
// the API as function pointers and get them with GetProcAddress calls 
// from kernel32.dll.  We also need to set some #defines.

#define XSTATE_AVX                          (XSTATE_GSSE)
#define XSTATE_MASK_AVX                     (XSTATE_MASK_GSSE)

typedef DWORD64 (WINAPI *PGETENABLEDXSTATEFEATURES)();
PGETENABLEDXSTATEFEATURES pfnGetEnabledXStateFeatures = NULL;

typedef BOOL (WINAPI *PINITIALIZECONTEXT)(PVOID Buffer, DWORD ContextFlags, PCONTEXT* Context, PDWORD ContextLength);
PINITIALIZECONTEXT pfnInitializeContext = NULL;
    
typedef BOOL (WINAPI *PGETXSTATEFEATURESMASK)(PCONTEXT Context, PDWORD64 FeatureMask);
PGETXSTATEFEATURESMASK pfnGetXStateFeaturesMask = NULL;

typedef PVOID (WINAPI *LOCATEXSTATEFEATURE)(PCONTEXT Context, DWORD FeatureId, PDWORD Length);
LOCATEXSTATEFEATURE pfnLocateXStateFeature = NULL;
    
typedef BOOL (WINAPI *SETXSTATEFEATURESMASK)(PCONTEXT Context, DWORD64 FeatureMask);
SETXSTATEFEATURESMASK pfnSetXStateFeaturesMask = NULL;
    
VOID
PrintThreadAvxState (
    __in HANDLE hThread
    )
{
    PVOID Buffer;
    PCONTEXT Context;
    DWORD ContextSize;
    DWORD64 FeatureMask;
    DWORD FeatureLength;
    ULONG Index;
    BOOL Success;
    PM128A Xmm;
    PM128A Ymm;

    // If this function was called before and we were not running on 
    // at least Windows 7 SP1, then bail.
    if (pfnGetEnabledXStateFeatures == (PGETENABLEDXSTATEFEATURES)-1)
    {
        _tprintf(_T("This needs to run on Windows 7 SP1 or greater.\n"));
        return;
    }

    // Get the addresses of the AVX XState functions.
    if (pfnGetEnabledXStateFeatures == NULL)
    {
        HMODULE hm = GetModuleHandle(_T("kernel32.dll"));
        if (hm == NULL)
        {
            pfnGetEnabledXStateFeatures = (PGETENABLEDXSTATEFEATURES)-1;
            _tprintf(_T("GetModuleHandle failed (error == %d).\n"), GetLastError());
            return;
        }
        
        pfnGetEnabledXStateFeatures = (PGETENABLEDXSTATEFEATURES)GetProcAddress(hm, "GetEnabledXStateFeatures");
        pfnInitializeContext = (PINITIALIZECONTEXT)GetProcAddress(hm, "InitializeContext");
        pfnGetXStateFeaturesMask = (PGETXSTATEFEATURESMASK)GetProcAddress(hm, "GetXStateFeaturesMask");
        pfnLocateXStateFeature = (LOCATEXSTATEFEATURE)GetProcAddress(hm, "LocateXStateFeature");
        pfnSetXStateFeaturesMask = (SETXSTATEFEATURESMASK)GetProcAddress(hm, "SetXStateFeaturesMask");
        
        if (pfnGetEnabledXStateFeatures == NULL
            || pfnInitializeContext == NULL
            || pfnGetXStateFeaturesMask == NULL
            || pfnLocateXStateFeature == NULL
            || pfnSetXStateFeaturesMask == NULL)
        {
            pfnGetEnabledXStateFeatures = (PGETENABLEDXSTATEFEATURES)-1;
            _tprintf(_T("This needs to run on Windows 7 SP1 or greater.\n"));
            return;
        }
    }
    
    FeatureMask = pfnGetEnabledXStateFeatures();
    if ((FeatureMask & XSTATE_MASK_AVX) == 0)
    {
        _tprintf(_T("The AVX feature is not enabled.\n"));
        return;
    }

    ContextSize = 0;
    Success = pfnInitializeContext(NULL,
                                   CONTEXT_ALL | CONTEXT_XSTATE,
                                   NULL,
                                   &ContextSize);

    if ((Success == TRUE) || (GetLastError() != ERROR_INSUFFICIENT_BUFFER))
    {
        _tprintf(_T("Unexpected result from InitializeContext (success == %d, error == %d).\n"),
                 Success,
                 GetLastError());
    }

    Buffer = malloc(ContextSize);
    if (Buffer == NULL)
    {
        _tprintf(_T("Out of memory.\n"));
        return;
    }

    Success = pfnInitializeContext(Buffer,
                                   CONTEXT_ALL | CONTEXT_XSTATE,
                                   &Context,
                                   &ContextSize);

    if (Success == FALSE)
    {
        _tprintf(_T("InitializeContext failed (error == %d).\n"), GetLastError());
        goto Cleanup;
    }

    Success = pfnSetXStateFeaturesMask(Context, XSTATE_MASK_AVX);
    if (Success == FALSE)
    {
        _tprintf(_T("SetXStateFeaturesMask failed (error == %d).\n"), GetLastError());
        goto Cleanup;
    }
    
    Success = GetThreadContext(hThread, Context);
    // Note: Thread state may not be accurate. For best results, suspend 
    // the thread and use the CONTEXT_EXCEPTION_REQUEST flags prior to 
    // calling GetThreadContext.
    if (Success == FALSE)
    {
        _tprintf(_T("GetThreadContext failed (error == %d).\n"), GetLastError());
        goto Cleanup;
    }

    Success = pfnGetXStateFeaturesMask(Context, &FeatureMask);
    if (Success == FALSE)
    {
        _tprintf(_T("GetXStateFeatureMask failed (error == %d).\n"), GetLastError());
        goto Cleanup;
    }

    //
    // The AVX feature consists of 8 (x86) or 16 (x64) 256-bit Ymm registers.
    // The lower 128 bits share storage with the corresponding Xmm (SSE)
    // registers and the high 128 bits are denoted by Ymm_H0 - Ymm_Hn.
    //

    if ((FeatureMask & XSTATE_MASK_AVX) == 0)
    {
        _tprintf(_T("AVX is in the INIT state (YMM_H registers are all zero).\n"));
        goto Cleanup;
    }

    Xmm = (PM128A)pfnLocateXStateFeature(Context, XSTATE_LEGACY_SSE, &FeatureLength);
    Ymm = (PM128A)pfnLocateXStateFeature(Context, XSTATE_AVX, NULL);

    //
    // Print values in the YMM registers.
    //

    for (Index = 0; Index < FeatureLength / sizeof(Xmm[0]); Index += 1)
    {
        _tprintf(_T("Ymm%d: %I64d %I64d %I64d %I64d\n"),
                 Index,
                 Xmm[Index].Low,
                 Xmm[Index].High,
                 Ymm[Index].Low,
                 Ymm[Index].High);
    }

Cleanup:
    free(Buffer);
    return;
} 

Rubriques connexes

CopyContext

InitializeContext

GetEnabledXStateFeatures

LocateXStateFeature

GetXStateFeaturesMask

SetXStateFeaturesMask