Re: [PATCH] left shift of negative value do_binop src/arith_yacc.c:111:12

01/08/25 00:50, Harald van Dijk wrote:
> On 31/07/2025 19:49, Aleksander Ushakov wrote:
>> There is a fix of the problem:
>>
>> diff --git a/src/arith_yacc.c b/src/arith_yacc.c
>> index 1a087c3..e23060d 100644
>> --- a/src/arith_yacc.c
>> +++ b/src/arith_yacc.c
>> @@ -108,7 +108,9 @@ static intmax_t do_binop(int op, intmax_t a, 
>> intmax_t b)
>>          case ARITH_SUB:
>>                  return a - b;
>>          case ARITH_LSHIFT:
>> -               return a << b;
>> +               if (a < 0)
>> +                       yyerror("left shift of negative value");
>> +               return (intmax_t)a << b;
>>          case ARITH_RSHIFT:
>>                  return a >> b;
>>          case ARITH_LT:
> If other major shells already issued an error here, this change would 
> look fine (except again incomplete -- there is a lot more potential to 
> trigger sanitizer messages in this file), but as other major shells 
> accept this, I think dash should continue to accept this too.
> 
> Cheers,
> Harald van Dijk

Well, if we take bash with UBSAN instrumentation and try to use a 
similar command with a negative number shift to the left, then at least 
we won't get a sanitizer error. Yes, you can remove the message that 
this shift is invalid, but it is still UB to perform this shift 
according to the C standard. I mean, a check should be added here so as 
not to trigger UBSAN, as it is done in bash.