Re: [Qemu-devel] [PATCH] bitops: fix types

[Blue Swirl]

On Sun, Jul 8, 2012 at 7:32 PM, Peter Maydell <address@hidden> wrote:
> On 8 July 2012 20:12, Blue Swirl <address@hidden> wrote:
>> On Sun, Jul 8, 2012 at 6:54 PM, Peter Maydell <address@hidden> wrote:
>>> On 8 July 2012 19:32, Blue Swirl <address@hidden> wrote:
>>>> On Sun, Jul 8, 2012 at 2:04 PM, Peter Maydell <address@hidden> wrote:
>>>>> On 8 July 2012 13:12,  <address@hidden> wrote:
>>>>>> -static inline uint64_t deposit64(uint64_t value, int start, int length,
>>>>>> -                                 uint64_t fieldval)
>>>>>> +static inline uint64_t deposit64(uint64_t value, unsigned int start,
>>>>>> +                                 unsigned int length, uint64_t fieldval)
>>>>>>  {
>>>>>>      uint64_t mask;
>>>>>> -    assert(start >= 0 && length > 0 && length <= 64 - start);
>>>>>> +    assert(length > 0 && length <= 64 - start);
>>>>>
>>>>> This breaks the assertion (consider the case of start == UINT_MAX
>>>>> and length == 64).
>>>>
>>>> The original is equally buggy in other cases since there is no bound
>>>> check for the upper limit.
>>>
>>> For what upper limit? Overlong length or start should both be caught
>>> by the third condition in the signed case.
>>
>> Nice. Why is it written like that, I'd use
>> start + length <= 64?
>
> That would fail to handle the case of start == length == INT_MAX.

 64 - INT_MAX = 0x80000040 (maybe off by one), which should still
trigger assert(INT_MAX <= 0x80000040)

>
> -- PMM