Request for reviews (S): 6973308: Missing zero length check before repne scas in check_klass_subtype_slow_path()

[Vladimir Kozlov]

Thank you, Tom

Vladimir

On 7/29/10 6:18 PM, Tom Rodriguez wrote:
> Looks good.
>
> tom
>
> On Jul 29, 2010, at 4:39 PM, Vladimir Kozlov wrote:
>
>> I updated webrev with additional changes in assembler_x86.cpp
>> to verify r12_heapbase even in zero based case.
>> These changes exposed this bug.
>>
>> Thanks,
>> Vladimir
>>
>> Vladimir Kozlov wrote:
>>> http://cr.openjdk.java.net/~kvn/6973308/webrev
>>> Fixed 6973308: Missing zero length check before repne scas in check_klass_subtype_slow_path()
>>> Z flag value will not be set by repne_scan(); if RCX == 0 since
>>> 'repne' instruction does not change flags (only scas instruction
>>> which is repeated sets flags).
>>> Setting Z = 1 before repne_scan() in check_klass_subtype_slow_path()
>>> will cause exception java.lang.IncompatibleClassChangeError:
>>>      // pointer were to sneak in here.  Note that we have already loaded the
>>>      // Klass::super_check_offset from the super_klass in the fast path,
>>>      // so if there is a null in that register, we are already in the afterlife.
>>> +    push(rax);
>>> +    xorq(rax,rax); // Set Z = 1
>>> +    pop(rax);
>>>      repne_scanl();
>>> % java -Xmx128M -jar GCBasher.jar -time:300
>>> Exception in thread "main" java.lang.IncompatibleClassChangeError
>>>         at java.lang.StringCoding$StringDecoder.decode(StringCoding.java:153)
>>> Solution:
>>> Instead of checking RCX for zero set Z = 0 (not equal) before 'repne'
>>> to indicate that class was not found when RCX == 0.
>>> Also fixed printed free stack size in hs_err files.
>>> Added ability to abort VM only on the exception with specific message.
>>> Tested with failed case.
>