[v2,AArch64] Add more debugging output to aarch64_displaced_step_fixup

  New in v2:

- Fixed misc comments from review.

--

While debugging the step-over-syscall problem, i wanted to see a bit more
debugging output to try to determine the root cause.

This patch does this.

gdb/ChangeLog:

2020-01-13  Luis Machado  <luis.machado@linaro.org>

	* aarch64-tdep.c (aarch64_displaced_step_fixup): Add more debugging
	output.
---
 gdb/aarch64-tdep.c | 27 +++++++++++++++++++++++++--
 1 file changed, 25 insertions(+), 2 deletions(-)
  

Ok to push.

Alan.

> On 13 Jan 2020, at 17:42, Luis Machado <luis.machado@linaro.org> wrote:
> 
> New in v2:
> 
> - Fixed misc comments from review.
> 
> --
> 
> While debugging the step-over-syscall problem, i wanted to see a bit more
> debugging output to try to determine the root cause.
> 
> This patch does this.
> 
> gdb/ChangeLog:
> 
> 2020-01-13  Luis Machado  <luis.machado@linaro.org>
> 
> 	* aarch64-tdep.c (aarch64_displaced_step_fixup): Add more debugging
> 	output.
> ---
> gdb/aarch64-tdep.c | 27 +++++++++++++++++++++++++--
> 1 file changed, 25 insertions(+), 2 deletions(-)
> 
> diff --git a/gdb/aarch64-tdep.c b/gdb/aarch64-tdep.c
> index 6a9d34dc67..29b712c155 100644
> --- a/gdb/aarch64-tdep.c
> +++ b/gdb/aarch64-tdep.c
> @@ -3037,8 +3037,16 @@ aarch64_displaced_step_fixup (struct gdbarch *gdbarch,
> 
>   regcache_cooked_read_unsigned (regs, AARCH64_PC_REGNUM, &pc);
> 
> +  if (debug_displaced)
> +    debug_printf ("Displaced: PC after stepping: %s (was %s).\n",
> +		  paddress (gdbarch, pc), paddress (gdbarch, to));
> +
>   if (dsc->cond)
>     {
> +      if (debug_displaced)
> +	debug_printf ("Displaced: [Conditional] pc_adjust before: %d\n",
> +		      dsc->pc_adjust);
> +
>       if (pc - to == 8)
> 	{
> 	  /* Condition is true.  */
> @@ -3050,8 +3058,18 @@ aarch64_displaced_step_fixup (struct gdbarch *gdbarch,
> 	}
>       else
> 	gdb_assert_not_reached ("Unexpected PC value after displaced stepping");
> +
> +      if (debug_displaced)
> +	debug_printf ("Displaced: [Conditional] pc_adjust after: %d\n",
> +		      dsc->pc_adjust);
>     }
> 
> +  if (debug_displaced)
> +    debug_printf ("Displaced: %s PC by %d\n",
> +		  dsc->pc_adjust? "adjusting" : "not adjusting",
> +		  dsc->pc_adjust);
> +
> +
>   if (dsc->pc_adjust != 0)
>     {
>       /* Make sure the previous instruction was executed (that is, the PC
> @@ -3059,11 +3077,16 @@ aarch64_displaced_step_fixup (struct gdbarch *gdbarch,
> 	 offset.  Otherwise we may skip an instruction before its execution
> 	 took place.  */
>       if ((pc - to) == 0)
> -	dsc->pc_adjust = 0;
> +	{
> +	  if (debug_displaced)
> +	    debug_printf ("Displaced: PC did not move. Discarding PC "
> +			  "adjustment.\n");
> +	  dsc->pc_adjust = 0;
> +	}
> 
>       if (debug_displaced)
> 	{
> -	  debug_printf ("displaced: fixup: set PC to %s:%d\n",
> +	  debug_printf ("Displaced: fixup: set PC to %s:%d\n",
> 			paddress (gdbarch, from), dsc->pc_adjust);
> 	}
>       regcache_cooked_write_unsigned (regs, AARCH64_PC_REGNUM,
> -- 
> 2.17.1
>