Access Violation with PInvoke

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Hello guys.

i'm working with TSAPI (alcatel) over C# (C/C++ works fine), but i'm having problem with access violation, see my code..

Windows PInvoke

C#

[Flags()]
public enum AllocationType : uint
{
    COMMIT = 0x1000,
    RESERVE = 0x2000,
    RESET = 0x80000,
    LARGE_PAGES = 0x20000000,
    PHYSICAL = 0x400000,
    TOP_DOWN = 0x100000,
    WRITE_WATCH = 0x200000
}
[Flags()]
public enum MemoryProtection : uint
{
    EXECUTE = 0x10,
    EXECUTE_READ = 0x20,
    EXECUTE_READWRITE = 0x40,
    EXECUTE_WRITECOPY = 0x80,
    NOACCESS = 0x01,
    READONLY = 0x02,
    READWRITE = 0x04,
    WRITECOPY = 0x08,
    GUARD_Modifierflag = 0x100,
    NOCACHE_Modifierflag = 0x200,
    WRITECOMBINE_Modifierflag = 0x400
}
[DllImport("kernel32.dll", SetLastError = true)]
static extern unsafe UIntPtr VirtualAlloc(uint lpAddress, uint dwSize,
   AllocationType flAllocationType, MemoryProtection flProtect);

TSAPI PInvoke

C#

[DllImport("csta32.dll", CallingConvention = CallingConvention.StdCall)]
public static extern unsafe int acsGetEventPoll(uint acsHandle, void* eventBuf, void *eventBufSize, void* privData, void* numEvents);

MyCode C# unsafe code

C#

byte* eventBuf = (byte*)VirtualAlloc(0, 1024, AllocationType.COMMIT | AllocationType.RESERVE, MemoryProtection.EXECUTE_READWRITE);

ushort* eventBufSize = (ushort*)VirtualAlloc(0, 2, AllocationType.COMMIT | AllocationType.RESERVE, MemoryProtection.EXECUTE_READWRITE); ;
*eventBufSize = 1024;

ushort* numEvents = (ushort*)VirtualAlloc(0, 2, AllocationType.COMMIT | AllocationType.RESERVE, MemoryProtection.EXECUTE_READWRITE); ;
*numEvents = 0;

void *privData = (byte*)VirtualAlloc(0, 1024, AllocationType.COMMIT | AllocationType.RESERVE, MemoryProtection.EXECUTE_READWRITE);

// acsHandle is OK
acsGetEventPoll(acsHandle, eventBuf, eventBufSize, privData, numEvents); // Attempted to read or write protected memory. This is often an indication that other memory is corrupt.

Some ideia????

Posted 28-Nov-14 1:02am

theafien

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Comments

nv3 28-Nov-14 8:04am

Have you checked the return values of your calls to VirtualAlloc? If any of these calls return 0, that would explain your access vialoation in acsGetEventPoll.

theafien 28-Nov-14 12:25pm

yes, VirtualAlloc correctly allocates memory

KarstenK 28-Nov-14 10:16am

Are the (in) buffer big enough?

why isnt privData set with a proper value or null?

theafien 28-Nov-14 12:24pm

all buffer is sufficient

Bernhard Hiller 28-Nov-14 10:50am

Did you check other CallingConvertions than CallingConvention.StdCall?
And that *numEvents = 0; looks somehow odd. Is it actually an "out int numEvents"?

theafien 28-Nov-14 12:24pm

Yes, all calling converntion has tested. *numEvents is to clear memory space.

[no name] 28-Nov-14 11:36am

Why the need for VirtualAlloc? Why do you need to execute permission for this memory?

theafien 28-Nov-14 12:23pm

I tested it with full permission, but still remains the problem.

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bling · Answer 1 · 2014-11-28T06:46:00

Try the Marshal functions instead of VirtualAlloc. Also, use IntPtr instead of void * for eventBuf and privData. Try a "ref ushort" for eventBufSize and numEvents.

C#

[DllImport("csta32.dll", CallingConvention = CallingConvention.StdCall)]
public static extern unsafe int acsGetEventPoll(uint acsHandle, IntPtr eventBuf, ref ushort eventBufSize, IntPtr privData, ref ushort numEvents);

ushort numEvents = 0;
ushort eventBufSize = 100; 
ushort privDataSize = 100;
IntPtr eventBuf = Marshal.AllocHGlobal(eventBufSize);
IntPtr privData = Marshal.AllocHGlobal(privDataSize);

int result = acsGetEventPoll(acsHandle, eventBuf, ref eventBufSize, privData, ref numEvents);

Marshal.FreeHGlobal (eventBuf);
Marshal.FreeHGlobal (privData);

I have no idea how large eventBufSize and privDataSize should be.