Re: [PATCH] Diagnose invalid pointer arithmetic on gdb.Value

[Pedro Alves <palves at redhat dot com>]

On 09/20/2016 05:19 PM, Jonathan Wakely wrote:
> On 20/09/16 16:41 +0100, Pedro Alves wrote:
>> On 09/20/2016 03:46 PM, Jonathan Wakely wrote:
>>> Instead of passing invalid arguments to value_binop and getting a
>>> misleading error, raise a TypeError directly in valpy_binop_throw.
>>
>> Did you try changing value_binop instead?  The error string seems
>> misleading even in C:
>>
>> (gdb) p ptr
>> $1 = 0x601040 <buf> ""
>> (gdb) p ptr + 1
>> $2 = 0x601041 <buf+1> ""
>> (gdb) p ptr + 1.0
>> Argument to arithmetic operation not a number or boolean.
>> (gdb)
> 
> Ah, so it's not specific to the Python API, in which case changing
> value_binop (or scalar_binop more accurately) might make sense.
> The check in scalar_binop *does* check for numbers, so the error is
> accurate. The argument that triggers the errors is actually the
> pointer argument, not the float one:
> 
>  if ((TYPE_CODE (type1) != TYPE_CODE_FLT
>       && TYPE_CODE (type1) != TYPE_CODE_DECFLOAT
>       && !is_integral_type (type1))
>      || (TYPE_CODE (type2) != TYPE_CODE_FLT
>       && TYPE_CODE (type2) != TYPE_CODE_DECFLOAT
>       && !is_integral_type (type2)))
>    error (_("Argument to arithmetic operation not a number or boolean."));
> 
> 
> The problem is that pointer arithmetic with invalid operands ends up
> here, because value_ptr{add,sub,diff} don't get called for invalid
> arguments.
> 
> So maybe a better fix is to first check if either argument is a
> pointer and give a more specific error, as attached (untested).
> 

Makes sense to me.

Thanks,
Pedro Alves