Re: [PATCH v7.1] Support software single step on ARM in GDBServer.

[Antoine Tremblay <antoine dot tremblay at ericsson dot com>]

On 12/11/2015 10:06 AM, Antoine Tremblay wrote:
> On 12/11/2015 09:43 AM, Yao Qi wrote:
> > Antoine Tremblay <antoine.tremblay@ericsson.com> writes:
> >
> > > +  /* Assume all atomic sequences start with a ldrex{,b,h,d}
> > > instruction.  */
> > > +  insn1 = self->ops->read_memory_unsigned_integer (loc, 2,
> > > byte_order_for_code);
> > > +
> > > +  loc += 2;
> > > +  if (thumb_insn_size (insn1) != 4)
> > > +    return NULL;
> > > +
> > > +  insn2 = self->ops->read_memory_unsigned_integer (loc, 2,
> > > byte_order_for_code);
> > > +
> >
> > This line is too long, you may define a macro to shorten
> > "self->ops->read_memory_unsigned_integer".
>
> This line is 79 long. From the GNU coding standard : "Please keep the
> length of source lines to 79 characters or less"
>
> So I think it's ok.
>
> I'm not sure a macro is a good thing, it often makes the code harder to
> parse for ides/emacs etc...
>
> And I don't think shortening the lines is a good justification in
> general for a macro.
>
> How about I use a function pointer variable like :
>
> ULONGEST (*read_memory_uint) (CORE_ADDR memaddr, int len, int byte_order);
>
> read_memory_uint = self->ops->read_memory_unsigned_integer;
>
> That would be already 23 shorter.
>
> > > +  loc += 2;
> > > +  if (!((insn1 & 0xfff0) == 0xe850
> > > +        || ((insn1 & 0xfff0) == 0xe8d0 && (insn2 & 0x00c0) == 0x0040)))
> > > +    return NULL;
> > > +
> > > +  /* Assume that no atomic sequence is longer than
> > > "atomic_sequence_length"
> > > +     instructions.  */
> > > +  for (insn_count = 0; insn_count < atomic_sequence_length;
> > > ++insn_count)
> > > +    {
> > > +      insn1
> > > +    = self->ops->read_memory_unsigned_integer (loc,
> > > 2,byte_order_for_code);
> > > +      loc += 2;
> > > +
> > > +      if (thumb_insn_size (insn1) != 4)
> > > +    {
> > > +      /* Assume that there is at most one conditional branch in the
> > > +         atomic sequence.  If a conditional branch is found, put a
> > > +         breakpoint in its destination address.  */
> > > +      if ((insn1 & 0xf000) == 0xd000 && bits (insn1, 8, 11) != 0x0f)
> > > +        {
> > > +          if (last_breakpoint > 0)
> > > +        return NULL; /* More than one conditional branch found,
> > > +                 fallback to the standard code.  */
> > > +
> > > +          breaks[1] = loc + 2 + (sbits (insn1, 0, 7) << 1);
> > > +          last_breakpoint++;
> > > +        }
> > > +
> > > +      /* We do not support atomic sequences that use any *other*
> > > +         instructions but conditional branches to change the PC.
> > > +         Fall back to standard code to avoid losing control of
> > > +         execution.  */
> > > +      else if (thumb_instruction_changes_pc (insn1))
> > > +        return NULL;
> > > +    }
> > > +      else
> > > +    {
> > > +      insn2 = self->ops->read_memory_unsigned_integer
> > > +        (loc, 2, byte_order_for_code);
> >
> > Format looks wrong, multiple instances of this problem in the patch.
>
> Yes actually I was not sure about that and discussed this with Pedro and
> he agreed this was ok. That's why I went with that.
>
> At some point when you have
> if
>    if
>       if
>          long_function_name (long variable,
>
> And that does not fit you could have
>
>          long_function_name (
>         long variable, ... )
>
> or      long_function_name
>         (long variable, ...)
>
> or ?
>
> I went with the latter after discussion with Pedro but I'm open to
> suggestions.
>
> Possibly the change to function pointers variables would make this moot
> but I think it may still happen.

I just tried to use indent for guidance on this (default gnu style)

and got this in the worst case :

insn2 =
  self->ops->
  read_memory_unsigned_integer
  (loc, 2, byte_order_for_code);

So while it did in the end put the function arguments below the 
function, it preferred splitting everywhere else before that.

I'm a bit surprised, however, that it has cut before = rather than after 
it, same surprise with -> ?

Honestly, however, I do think it's much clearer to write

insn2 = self->ops->read_memory_unsigned_integer
  (loc, 2, byte_order_for_code);

Then to split it up at = and ->

Ideas are welcome.

Thanks,
Antoine