Re: ARM stack alignment on hand called functions

[Andrew Cagney <ac131313@redhat.com>]

> 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.

Kris, FYI,
It's very important to always reproduce problems using the current GDB 
sources.  That way, any confusion arrising from either local 
modifications (does QNX 6 ship an un-modified GDB 5.2.1?) or out-of-date 
sources (has the problem been fixed?).

For the problem at hand, I suspect the post 5.3 architecture method - 
gdbarch_frame_align() - is needed.  That method is used to align each 
element's stack address (e.g., struct return) and not the size of each 
element.

(I think I might add a few more juicy comments to valops.c so its 
clearer what the fix to your problem is :-).

Andrew

(1) BTW, note:
http://sources.redhat.com/gdb/current/onlinedocs/gdbint_15.html#SEC130
To avoid version conflicts, vendors are expected to modify the file 
`gdb/version.in' to include a vendor unique alphabetic identifier (an 
official GDB release never uses alphabetic characters in its version 
identifer).



> 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;
>   }
> 
> The code in valops.c : hand_function_call() that was causing the problem was
> this:
> 
>   /* Reserve space for the return structure to be written on the
>      stack, if necessary */
>   if (struct_return)
>     {
>       int len = TYPE_LENGTH (value_type);
>       if (STACK_ALIGN_P ())
>  /* MVS 11/22/96: I think at least some of this stack_align
>     code is really broken.  Better to let PUSH_ARGUMENTS adjust
>     the stack in a target-defined manner.  */
>  len = STACK_ALIGN (len);
>       if (INNER_THAN (1, 2))
>  {
>    /* stack grows downward */
>    sp -= len;
>    struct_addr = sp;
>  }
> 
> So what I did was to make sure that arm_push_arguments would always return
> an aligned stack pointer.  I think we can safely agree that
> arm_push_arguments should NEVER return an unaligned stack pointer right?
> 
> cheers,
> 
> Kris
> 
>