Re: [try 2nd 5/8] Displaced stepping for Thumb 32-bit insns

["Ulrich Weigand" <uweigand at de dot ibm dot com>]

Yao Qi wrote:
> On 09/14/2011 09:39 PM, Ulrich Weigand wrote:
> >> >    1.  Failures in gdb.arch/thumb2-it.exp and gdb.base/gdb1555.exp. 
> >> > These failures are caused by missing IT support in thumb displaced stepping.
> > Ah, right.  Fortunately, I think IT support should be relatively easy to
> > add, in fact we should be able to just completely emulate it:
> > 
> > - The first thing we do when we're about to displaced-step a Thumb insn
> >   is to check the itstate and see whether we're in an IT block.
> > 
> > - If so, we check whether the condition is true, given the current state
> >   of the flags.
> > 
> > - If the condition is false, we always use a NOP as the displaced
> >   instruction; otherwise, compute the displaced instruction as usual.
> > 
> > - In either case, set the CSPR register as if we're outside of any
> >   IT block while actually executing the displaced instruction.  (This
> >   also makes sure that the breakpoint at the end will always be
> >   executed.)
> > 
> > - During fixup after execution is done, re-set IT state in the CSPR
> >   to the proper value (advanced by one instruction).
> > 
> > See also thumb_get_next_pc_raw for how to manipulate IT state ...
> > 
> > Does this look good to you?
> > 
> 
> Yes, it looks right to me in general.  However, it doesn't handle the
> case of `stepi' in condition blocks when displaced stepping is enabled,
> as gdb.arch/thumb2-it.exp tested.  We expect inferior stops at the next
> true-condition instruction instead of next instruction after typing
> `stepi'.  In this design, inferior will stop at the next instruction
> regardless of condition.  We may adjust PC value in fixup to skip these
> false-condition instructions.

OK, good point.  I agree.

Thanks,
Ulrich

-- 
  Dr. Ulrich Weigand
  GNU Toolchain for Linux on System z and Cell BE
  Ulrich.Weigand@de.ibm.com