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.NET Forum / .NET Framework / CLR / November 2005CIL, CopyMemory and Compact Framework
Hi, I'm trying to write a method for my PocketPC that will write a Double value to an Array buffer at the specified offset. The constraints are : - Must be safe managed code - Array buffer can be of any integral type (byte, short, int, long, etc.) - offset can be unaligned I already wrote this method for Win32, and it works fine. Because I knew about alignement constraint on ARM processors, I rewrote the method doing a loop on the 8 bytes of the double value like do the BitConverter.ToDouble method in its Compact Framewrok version The differences between BitConverter.ToDouble and my method are: - I'm writing a SetDouble method - The destination buffer is an Array of any integral type (not only a Byte[]) My Compact Framework version of SetDouble works fine on the Pocket PC 2002 emulator, but throws a 0x80000002 exception on my Pocket PC device (QTEK 9090) Here is the method code I wrote (I know that I'm accessing the Array like a Byte array, but only for the first element in order to retreive the array's starting address. This works fine in my Windows.Forms version): .method public hidebysig static void SetDouble(class [mscorlib]System.Array buffer, int32 offset, float64 'value') cil managed { .locals (unsigned int8* pBuffer, int32 nIndex, unsigned int8* pValue) ldarg.0 ldc.i4.0 ldelema [mscorlib]System.Byte ldarg.1 add stloc.0 ldc.i4.0 stloc.1 ldarga.s 2 stloc.2 LOOP: ldloc.0 ldloc.1 add ldloc.2 ldloc.1 add ldind.i1 stind.i1 ldloc.1 ldc.i4.1 add stloc.1 ldloc.1 ldc.i4.8 blt.s LOOP ret } // end of method Buffer::SetDouble Any suggestion ? Thanks a lot First of all, I'm using .Net Framework v1.1 with VS.NET 2003 I have made some tests, and I realized that "ldelema [mscorlib]System.Byte" doesn't work on my Pocket PC device if my buffer is declared as follow even if typeof(buffer) is Byte[]: SetDouble(class [mscorlib]System.Array buffer,... It does work if the buffer is declared as follow: SetDouble(unsigned int8[] buffer,... Here is the code of my method. It works on Win32 and Compact Framwork in the emulator, but not on my Pocket PC device .method public hidebysig static void SetDouble(class [mscorlib]System.Array buffer, // SetDouble(unsigned int8[] buffer, int32 offset, float64 'value') cil managed { .locals (int32 nIndex, unsigned int8* pValue, unsigned int8* pBuffer) ldc.i4.0 // 0 stloc.0 // nIndex = 0 ldarga.s 2 // &value stloc.1 // pValue = &value; ldarg.0 // buffer ldarg.1 // offset ldelema [mscorlib]System.Byte // &buffer[offset] stloc.2 // pBuffer = &buffer[offset] LOOP: ldloc.2 // pBuffer ldloc.0 // nIndex add // pBuffer + nIndex ldloc.1 // pValue ldloc.0 // nIndex add // &pValue[nIndex] ldind.i1 // pValue[nIndex] stind.i1 // pBuffer[nIndex] = pValue[nIndex] ldloc.0 // nIndex ldc.i4.1 // 1 add // nIndex++ stloc.0 // ->nIndex ldloc.0 // nIndex ldc.i4.8 // 8 blt.s LOOP // if (nIndex < 8) goto LOOP ret } // end of method Buffer::SetDouble > Hi, > [quoted text clipped - 69 lines] > > Thanks a lot > I'm trying to write a method for my PocketPC that will write a Double value > to an Array buffer at the specified offset. Any reason you're not calling System.Buffer.BlockCopy ? Mattias The main reason is that the source or destination is not an Array > > I'm trying to write a method for my PocketPC that will write a Double value > > to an Array buffer at the specified offset. > > Any reason you're not calling System.Buffer.BlockCopy ? > > Mattias >The main reason is that the source or destination is not an Array Looks to me like the destination is an array and you said so yoruself in your original message. The source value isn't an array but nothing's stopping you from putting it into a single element double[]. Mattias  SignatureMattias Sjögren [MVP] mattias @ mvps.org http://www.msjogren.net/dotnet/ | http://www.dotnetinterop.com Please reply only to the newsgroup. > I'm trying to write a method for my PocketPC that will write a Double > value > to an Array buffer at the specified offset. > > The constraints are : > - Must be safe managed code Do you mean verifiable code? Or just valid CIL? > - Array buffer can be of any integral type (byte, short, int, long, etc.) > - offset can be unaligned > > I already wrote this method for Win32, and it works fine. > My Compact Framework version of SetDouble works fine on the Pocket PC 2002 > emulator, but throws a 0x80000002 exception on my Pocket PC device (QTEK [quoted text clipped - 5 lines] > array's > starting address. This works fine in my Windows.Forms version): Did you write that in MSIL assembler? Can you share the source? BTW: There's also unaligned > .method public hidebysig static void > SetDouble(class [mscorlib]System.Array buffer, > int32 offset, > float64 'value') cil managed > { > .locals (unsigned int8* pBuffer, int32 nIndex, unsigned int8* pValue) I don't think you can do anything verifiable with native pointers. And if you really want to use them, make sure the pointee is pinned. > ldarg.0 > ldc.i4.0 > ldelema [mscorlib]System.Byte That's probably not verifiable. You should cast to the array type before via ldarg.0 castclass unsigned int8[] ldc.i4.0 ldelema unsigned int8 ... > ldarg.1 > add (Managed) pointer arithmetic is not verifiable. > stloc.0 You store a managed pointer into a variable of native pointer type. You should only do so if you know the memory pointed to can't be moved by the GC. You might want to use unaligned.1 cpblk -hg Thank you very much for your time, here are some answers Lvt > Do you mean verifiable code? Or just valid CIL? LVT : I just want not to be bored if security constraints (like only managed code is allowed to run on this computer) are ON in .Net Framework > Did you write that in MSIL assembler? Can you share the source? LVT : Yes, I wrote this code in MSIL : First I wrote a small class with empty methods, then I used ILDASM to get the MSIL of my class with methods doing nothing, and then I wrote the missing MSIL code in my methods Here is the code of the C# class : using System; namespace Memory { public class Buffer { private Buffer() {} public static void SetDouble(Array buffer, Int32 offset, Double value) {} } } Here is the SetDouble generated code with my MSIL: .method public hidebysig static void SetDouble(class [mscorlib]System.Array buffer, int32 offset, float64 'value') cil managed { .locals (int32 nIndex, unsigned int8* pValue, unsigned int8* pBuffer) ldc.i4.0 // 0 stloc.0 // nIndex = 0 ldarga.s 2 // &value stloc.1 // pValue = &value; ldarg.0 // buffer ldarg.1 // offset ldelema [mscorlib]System.Byte // &buffer[offset] stloc.2 // pBuffer = &buffer[offset] LOOP: ldloc.2 // pBuffer ldloc.0 // nIndex add // pBuffer + nIndex ldloc.1 // pValue ldloc.0 // nIndex add // &pValue[nIndex] ldind.i1 // pValue[nIndex] stind.i1 // pBuffer[nIndex] = pValue[nIndex] ldloc.0 // nIndex ldc.i4.1 // 1 add // nIndex++ stloc.0 // ->nIndex ldloc.0 // nIndex ldc.i4.8 // 8 blt.s LOOP // if (nIndex < 8) goto LOOP ret } // end of method Buffer::SetDouble > BTW: There's also unaligned LVT: Yes, alignment is a big issue on ARM, that's why I used a loop The first version I wrote in MSIL for SetDouble was: IL_0000: ldarg.0 IL_0001: ldc.i4.0 IL_0002: ldelema [mscorlib]System.Byte IL_0007: ldarg.1 IL_0008: add IL_0009: ldarg.2 IL_000a: unaligned. 1 IL_000d: stind.r8 IL_000e: ret but this code throws an exception on my Pocket PC > I don't think you can do anything verifiable with native pointers. And > if you really want to use them, make sure the pointee is pinned. LVT: I don't know how to pin memory > That's probably not verifiable. You should cast to the array > type before via [quoted text clipped - 3 lines] > ldelema unsigned int8 > .... LVT : Unfortunately, I couldn't cast the Array because I don't know its type My first Idea was to provide a method that works on any integral type array, but I realize that drive me to a lot of problems for 'nothing'. I Think I will simply allow bytes array and then used Byte[] parameter type instead of Array type. This way I can use the ldelem.u1 just like BitConverter.ToDouble is doing in its CF version > (Managed) pointer arithmetic is not verifiable. > You store a managed pointer into a variable of native pointer > type. You should only do so if you know the memory pointed > to can't be moved by the GC. LVT: You're right and I will avoid pointer arithmetic with ldelem.u1 > You might want to use unaligned.1 cpblk LVT: Idealy YES but the following code throws an InvalidProgramException: .method public hidebysig static void SetDouble(unsigned int8[] buffer, int32 offset, float64 'value') cil managed { ldarg.0 // buffer ldarg.1 // offset ldelema [mscorlib]System.Byte // &buffer[offset] ldarga.s 2 // &value ldc.i4.8 // 8 unaligned. 1 cpblk // CopyMemory ret } // end of method Buffer::SetDouble > > I'm trying to write a method for my PocketPC that will write a Double > > value [quoted text clipped - 55 lines] > > -hg >> Do you mean verifiable code? Or just valid CIL? > LVT : I just want not to be bored if security constraints (like only > managed > code is allowed to run on this computer) are ON in .Net Framework You probably want your code to verifiable then. Almost none of the things suggested in here will work then. Maybe there are some base library helpers which are statically known to be safe, but I'm afraid you'll have to stick with a less efficient method. [snip] >> BTW: There's also unaligned > LVT: Yes, alignment is a big issue on ARM, that's why I used a loop Alignment is important on almost all platforms. > The first version I wrote in MSIL for SetDouble was: > [quoted text clipped - 9 lines] > > but this code throws an exception on my Pocket PC I don't see anything wrong here. What's the exception? Can you locate where it happens in the CIL stream? (You may want to ilasm with debug information /DEBUG) >> I don't think you can do anything verifiable with native pointers. And >> if you really want to use them, make sure the pointee is pinned. > LVT: I don't know how to pin memory You need a managed pointer with the pinned attribute to point to the object (or any subobject of the complete object). This can safely be converted to a native pointer. However, native pointers are never verifiable. .class X { // .ctor .field int32 f; } .method public static void main() { .entrypoint .locals ( int32& pinned p ) newobj instance void class X::.ctor() // x ldflda int32 X::f stloc p // x.f is now pinned => x is pinned ldloc p conv.u // top of the stack can be used as a native pointer ret } >> That's probably not verifiable. You should cast to the array >> type before via [quoted text clipped - 14 lines] > in > its CF version You can't do much with an array whose element type is unknown (in a verifiable way). >> You might want to use unaligned.1 cpblk > LVT: Idealy YES but the following code throws an InvalidProgramException: [quoted text clipped - 12 lines] > ret > } // end of method Buffer::SetDouble Looks perfectly valid to me. Did you get the calling function correct? What does peverify say? Unfortunately, I do not have time to spend on this issue right now (my clients are waiting for me...), I will investigate this later. For now, I just change Array type to Byte[] and use a 8 bytes loop just like BitConverter.ToDouble does. As you certainely guess, I'm new in MSIL coding, and I found your remarks very helpfull. Thank you very much Lvt > >> Do you mean verifiable code? Or just valid CIL? > > LVT : I just want not to be bored if security constraints (like only [quoted text clipped - 96 lines] > Looks perfectly valid to me. Did you get the calling function > correct? What does peverify say?
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