Re: [PATCH] gdb-power10-single-step

[Ulrich Weigand <uweigand@de.ibm.com>]

Will Schmidt wrote:

>   This is a patch written by Alan Modra.  With his permission
> I'm submitting this for review and helping get this upstream.
> 
> Powerpc / Power10 ISA 3.1 adds prefixed instructions, which
> are 8 bytes in length.  This is in contrast to powerpc previously
> always having 4 byte instruction length.  This patch implements
> changes to allow GDB to better detect prefixed instructions, and
> handle single stepping across the 8 byte instructions.

There's a few issues I see here:

- The patch now *forces* software single-stepping for all 8-byte
  instructions.  I'm not sure why this is necessary; I thought
  that hardware single-stepping was supported for 8-byte instructions
  as well?  That would certainly be preferable.

- However, the inner loop of ppc_deal_with_atomic_sequence should
  probably be updated to correctly skip 8-byte instructions; e.g.
  to avoid mistakenly recognizing the second word of an 8-byte
  instructions for a branch or store conditional.  (Also, the
  count of up to "16 instructions" is wrong if 8-byte instructions
  are not handled specifically.)

- In ppc_displaced_step_fixup 8-byte instructions are now recognized,
  and this is good as far as it goes.  However, there are some 8-byte
  instruction that have PC-relative semantics, and those will need
  an additional fixup.  (Note that this same fixup is already missing
  for the Power9 addpcis instruction, see bug 27525).

Bye,
Ulrich

-- 
  Dr. Ulrich Weigand
  GNU/Linux compilers and toolchain
  Ulrich.Weigand@de.ibm.com