Re: [Qemu-arm] [PATCH 1/3] decodetree: Allow !function with no input bits

[Richard Henderson]

On 8/9/19 8:52 AM, Peter Maydell wrote:
>> @@ -195,7 +195,10 @@ class MultiField:
>>      """Class representing a compound instruction field"""
>>      def __init__(self, subs, mask):
>>          self.subs = subs
>> -        self.sign = subs[0].sign
>> +        if len(subs):
>> +            self.sign = subs[0].sign
>> +        else:
>> +            self.sign = 0
>>          self.mask = mask
>>
>>      def __str__(self):
> Is this change to MultiField left over from the previous
> implementation ? I was expecting a zero-length MultiField
> to now be a bug in this python script (ie we should never
> try to create one).
> 

Oops, yes.

The error is emitted here:

> +    if len(subs) == 0:
> +        if func:
> +            f = ParameterField(func)
> +        else:
> +            error(lineno, 'field with no value')

and tested:

> +++ b/tests/decode/err_field6.decode
> @@ -0,0 +1,5 @@
> +# This work is licensed under the terms of the GNU LGPL, version 2 or later.
> +# See the COPYING.LIB file in the top-level directory.
> +
> +# Diagnose no bits in field
> +%field