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

Ulrich Weigand
2011-10-10T14:40:26Z

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