Request for review: 7110152 assert(size_in_words <= (julong)max_jint) failed: no overflow

[Bengt Rutisson]

...except that I just saw that CollectedHeap::array_allocate_nozero() 
uses int.

I'll fix that and update the webrev.

Bengt

On 2011-11-09 23:47, Bengt Rutisson wrote:
>
> Vladimir,
>
> Thanks for looking at this!
>
> On 2011-11-09 23:06, Vladimir Kozlov wrote:
>> Why not change it in all CollectedHeap methods?
>
> The other methods in CollectedHeap that use int for size are handling 
> objects. Those should not have been affected by my other change (since 
> it only changed the maximum array length).
>
> I have not investigated whether or not it is possible to create an 
> object (that is not an array) that will have a size larger than int. I 
> assume that there is some limit to how many fields an object can have. 
> But I don't know what that limit is and whether it will guarantee that 
> the largest object fits into an int. It also seems much more unlikely 
> that anyone would actually create such a large object.
>
> I'd like to only change this for arrays now since we have failures in 
> the nightlies. If you think it is ok I could create a separate CR to 
> investigate whether or not the int object sizes in CollectedHeap are 
> safe.
>
> Bengt
>
>>
>> Vladimir
>>
>> Bengt Rutisson wrote:
>>>
>>> Hi all,
>>>
>>> Could I have a couple of reviews for this small change?
>>> http://cr.openjdk.java.net/~brutisso/7110152/webrev.01/
>>>
>>> The problem is that CollectedHeap::array_allocate() takes its size 
>>> as an int instead of a size_t. This was exposed by the fix I made to 
>>> 7102044 recently.
>>>
>>> That change allows arrays to be max_jint long on 64 bit systems. 
>>> This is correct since we can handle this size in a 64 bit size_t 
>>> even when we add the object header. However, it will overflow an int.
>>>
>>> Here is a small reproducer that will trigger the assert mentioned in 
>>> 7110152 when it is run on a 64 bit VM:
>>>
>>> public class MaxJIntArray {
>>>     public static void main(String[] args) {
>>>         final int MAX_JINT = 2147483647;
>>>         double[] a = new double[MAX_JINT];
>>>         System.out.println("Allocated a[" + a.length + "]");
>>>     }
>>> }
>>>
>>> The fix is to remove the assert (since it is too strict) and 
>>> changing CollectedHeap::array_allocate() to take a size_t instead of 
>>> an int.
>>>
>>> CR:
>>> 7110152 assert(size_in_words <= (julong)max_jint) failed: no overflow
>>> http://monaco.sfbay.sun.com/detail.jsf?cr=7110152
>>>
>>> Bengt
>