[RFA] More tweaks to arm_skip_prologue

[Michael Snyder]

Richard Earnshaw wrote:
> 
> >
> > 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.

You know way more about the architecture than I do, but
check arm_scan_prologue -- it already does the same thing.
I'd like to bring them into sync, and then think about
possibly making them smarter.

> 
> >
> > !   /* 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). 

OK, I'll correct that.

> What about an "stmfd sp!, {...., lr}" (non-frame) prologue instruction.

Can you give me a pattern to match for?
I haven't actually seen that instruction in a prologue.