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To: "Kris Warkentin" <kewarken@qnx.com>
cc: Richard.Earnshaw@arm.com, gdb@sources.redhat.com
Reply-To: Richard.Earnshaw@arm.com
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Subject: Re: ARM stack alignment on hand called functions 
In-reply-to: Your message of "Wed, 20 Nov 2002 11:26:28 EST."
             <191601c290b1$942159e0$0202040a@catdog> 
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Date: Wed, 20 Nov 2002 10:37:00 -0000
From: Richard Earnshaw <rearnsha@arm.com>
X-SW-Source: 2002-11/txt/msg00277.txt.bz2

> The problem arises only with functions which return structures whose size is
> not evenly divisible by 4.  Below is what I did to solve it.
> 
> Index: arm-tdep.c
> ===================================================================
> RCS file: /product/tools/gdb/gdb/arm-tdep.c,v
> retrieving revision 1.9
> retrieving revision 1.10
> diff -c -r1.9 -r1.10
> *** arm-tdep.c  20 Sep 2002 17:11:31 -0000      1.9
> --- arm-tdep.c  19 Nov 2002 18:33:37 -0000      1.10
> ***************
> *** 1480,1485 ****
> --- 1480,1486 ----
>         }
>       }
> 
> +   sp = (sp + 3) & ~3;
>     /* Return adjusted stack pointer.  */
>     return sp;
>   }
> 

OK, but with this change the alignment is being done *after* any arguments 
that have to go onto the stack have been pushed.  It should happen 
*before*.  What happens if you have?

struct f { char a; char b; char c;};

struct f g = {1,2,3};

struct f h (int a, int b, int c, int d, int e)
{
  g.c = e;
  return g;
}

and then call h from within the debugger.  Is g.c set correctly?

My guess is that it won't, because the integer value for e will have been 
pushed onto the stack incorrectly.

R.