Re: [RFA] More tweaks to arm_skip_prologue

[Richard Earnshaw <rearnsha at arm dot com>]

> 
> I know that some of these tweaks to arm_skip_prologue will also
> suggest similar tweaks to arm_scan_prologue.  I'll do those next.
> Wouldn't it be nice if the two shared code?    ;-)
> 
> 2002-04-22  Michael Snyder  <msnyder@redhat.com>
> 
> 	* arm-tdep.c (arm_skip_prologue): Better handling for frameless 
> 	functions.  Treat "mov ip, sp" as optional.  Recognize 
> 	"str lr, [sp, #-nn]".
> 
In principal OK, but see embedded notes.

>        by disassembling the instructions. */
>     skip_pc = pc;
>     inst = read_memory_integer (skip_pc, 4);
> !   if (inst == 0xe1a0c00d)       /* mov ip, sp */
> !     {
> !       skip_pc += 4;
> !       inst = read_memory_integer (skip_pc, 4);
> !     }

If the sequence doesn't start with mov ip, sp then we either have a 
scheduled prologue where the first instruction is messing with 
call-clobbered register, or we have a frameless prologue.  I suspect that 
if are in this situation then we should use a different unwind function to 
keep things simpler.

>   
> !   /* Some prologues begin with "str lr, [sp, #-nn]".  */
> !   if ((inst & 0xffffff00) == 0xe52de000)        /* str lr, [sp, #-nn] */
>       {
>         skip_pc += 4;
>         inst = read_memory_integer (skip_pc, 4);
>       }

This should only ever be "str lr, [sp, #-4]!" (note the writeback).  What 
about an "stmfd sp!, {...., lr}" (non-frame) prologue instruction.

>   
> !   if ((inst & 0xfffffff0) == 0xe92d0000)	/* stmfd sp!,{a1,a2,a3,a4}  */
> !     {
> !       skip_pc += 4;
> !       inst = read_memory_integer (skip_pc, 4);
> !     }
>   
> !   if ((inst & 0xfffff800) == 0xe92dd800)	/* stmfd sp!,{fp,ip,lr,pc} */
> !     {
> !       skip_pc += 4;
> !       inst = read_memory_integer (skip_pc, 4);
> !     }
>   

R.