[Vm-dev] socketRecordSize is probably not 64-bit friendly

[David T. Lewis]

On Sun, Mar 22, 2015 at 01:58:05PM -0400, David T. Lewis wrote:
>  
> On Sun, Mar 22, 2015 at 05:04:12PM +0100, Nicolas Cellier wrote:
> >  
> > Hi,
> > I noticed that SocketPlugin>>socketRecordSize was so defined:
> > socketRecordSize
> >     "Return the size of a Smalltalk socket record in bytes."
> > 
> >     ^ self cCode: 'sizeof(SQSocket)' inSmalltalk: [12]
> > 
> > 
> > Shouldn't it have been like its brothers in OSProcessPlugin and AioPlugin:
> > 
> > socketRecordSize
> >     "Return the size of a Smalltalk socket record in bytes."
> > 
> >     ^ self cCode: 'sizeof(SQSocket)' inSmalltalk: [Smalltalk wordSize * 3]
> > 
> > 
> > I presume we don't use self sizeof: because the Smalltalk side does not
> > have any idea of what a SQSocket is... (an opaque struct/handle)
> 
> On my machine, sizeof(SQSocket) is 16 for both 32 bits and 64 bits. I would
> have expected it to be 12 for the 32-bit case, but maybe the compiler is
> aligning it differently for some reason.
> 
> In any case, "Smalltalk wordSize * 3" would not be right, because the
> actual data structure is this:
> 
> 	typedef struct
> 	{
> 	  int   sessionID;
> 	  int   socketType;  /* 0 = TCP, 1 = UDP */
> 	  void  *privateSocketPtr;
> 	}  SQSocket, *SocketPtr;
> 
> 
> In order to cover the common cases, it might be best to just change
> the implementation to this:
> 
>      ^ self cCode: 'sizeof(SQSocket)' inSmalltalk: [16]

Forgive me, I just realized that I was accidentally running a 64-bit
VM when I thought it was a 32-bit VM. So the size of a SQSocket will
typically be 12 bytes on a 32-bit host, and 16 bytes on a 64-bit host,
regardless of whether the image word size is 32-bit or 64-bit.

Dave