Prevent allocation of replaced classes #3143
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Objects on the heap must always point to the most current version of the J9Class. Prevent allocation of replaced classes by causing fast path allocations to fail for replaced classes. The final (slow path) allocator will use the most current version of the requested class to fix any callers who unwittingly passes a replaced class. [ci skip] Signed-off-by: Graham Chapman <graham_chapman@ca.ibm.com>
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jenkins test all zlinux jdk8 |
| @@ -77,7 +77,7 @@ class MM_JavaObjectAllocationModel : public MM_AllocateInitialization | |||
| if (NULL != objectPtr) { | |||
| /* Initialize class pointer in object header -- preserve flags set by base class */ | |||
| MM_GCExtensions *extensions = MM_GCExtensions::getExtensions(env); | |||
| extensions->objectModel.setObjectClass(objectPtr, _class); | |||
| extensions->objectModel.setObjectClass(objectPtr, getClass()); | |||
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Should the protected _class field become private to prevent subclass's from reaching for it directly? And likely commented to indicate the issue.
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Making the field private means modifying a lot of code. Any users of the field before a GC has occurred really don't need to get the current class (the OM is used in the faster path NoGC code as well).
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Tempted to add a new accessor getCurrentClass() for people who are aware that the class may change during a GC, and leave getClass() as it is (there are actually no callers - all access is by direct field fetch).
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@dmitripivkine I'm OK with taking this change as is. Do you want a followup issue to make the _class field private?
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yes, we will take care about this
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I will not make the accessor change now - you can decide if you want it when changing the field visibility.
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Once the testing passes, whoever sees it first can merge |
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Jenkins is struggling to complete builds. Merging now as the Sanity passed. |
Objects on the heap must always point to the most current version of the
J9Class. Prevent allocation of replaced classes by causing fast path
allocations to fail for replaced classes. The final (slow path)
allocator will use the most current version of the requested class to
fix any callers who unwittingly passes a replaced class.
[ci skip]
Signed-off-by: Graham Chapman graham_chapman@ca.ibm.com