volatile const structure members in C++
Steven L. Zook
SLZook@Qualstar.com
Fri Aug 26 17:14:00 GMT 2005
>From my original mail here is the code I get:
.globl _Z8FunctionR2sA
.type _Z8FunctionR2sA, @function
_Z8FunctionR2sA:
link.w %a6,#0
move.l 8(%a6),%a0 | A, A
move.l 4(%a0),%d0 | <variable>.C, <variable>.C
unlk %a6
rts
I am really getting a load of A.C but not of A.B. They are both volatile
members. Should they not both be loading?
-----Original Message-----
From: gcc-help-owner@gcc.gnu.org [mailto:gcc-help-owner@gcc.gnu.org] On
Behalf Of Ian Lance Taylor
Sent: Friday, August 26, 2005 9:58 AM
To: Daniel Berlin
Cc: Steve Zook; gcc-help@gcc.gnu.org
Subject: Re: volatile const structure members in C++
Daniel Berlin <dberlin@dberlin.org> writes:
> On Thu, 2005-08-25 at 21:24 -0700, Steve Zook wrote:
> > Using m68k-elf-gcc with either revision 3.3.3 or 3.4.4, I compile
> > the following test program (as a C++ program) at -O2 to an object
file:
> >
> >
> > struct sA { unsigned volatile const B;
> > unsigned volatile C;
> > unsigned const D;
> > unsigned E; };
> > void Function( sA & A ) { A.B; A.C; A.D; A.E; }
> >
> >
> > The object file I get looks like (edited for brevity):
> >
> > .globl _Z8FunctionR2sA
> > .type _Z8FunctionR2sA, @function
> > _Z8FunctionR2sA:
> > link.w %a6,#0
> > move.l 8(%a6),%a0 | A, A
>
> This is a load of A.B. It's the first member of the structure, and
> thus, is at offset 0, and is also known as "A".
No, that's a load of the address of A--i.e., loading the argument into a
register. On the m68k arguments are passed on the stack. To actually
load A.B, rather than just the address of A.B, would require a following
move.l 0(%a0),....
Ian
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