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

[Antoine Tremblay <antoine.tremblay@ericsson.com>]

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.

Thanks,
Antoine