Re: egcs and bitfields

["David A. Greene" <greened@eecs.umich.edu>]

Robert Lipe wrote:
> 
> > struct baz { unsigned int a:2, b:4, c:32;} y;
> >
> > void foo()
> > {
> >   y.c = 0x56789;
> > }
> >
> > int main()
> > {
> >   unsigned int  *b;
> >   bzero(&y,sizeof(y));
> >   foo();
> >   b=&y;
> >   printf("%x %x\n",b[0],b[1]);
> > }
> >
> > Is this the case you are talking about? Now, you claim that the SysV
> > ABI requires y.c to be at offset 4, right? (this is a claim I can't
> > verify since I don't have that specification)
> 
> "System V ABI" is too vague for purposes of this discussion.  Do you
> refer to the iBCS2 spec or the SVR4 ABI?  I don't know that they differ
> in this regard, but it isn't an unreasonable question before tearing
> into large books.

Good question.  The book I have here is the "System V ABI Intel386
Processor Supplement" put out by AT&T in 1991 (yes, I know it's old,
but it's all we've got).  It is the SVR4 ABI.  Please correct me 
if there's a more up-to-date version I should be looking at.
 
> I think (but am no authority) that Linux uses substantially the SVR4 ABI
> but it does have some deviations.

Do you know what these deviations are?  The devil is in the details. :)

                                           -Dave