[aarch64-port-dev ] RFR: fix for crash caused by earlyret of compiled method

[Andrew Haley]

On 13/06/17 14:24, Sergey Nazarkin wrote:
> Hi!
> 
> Please review the fix [1] for the crash happens when compiled method is forced to return early.  We found this issue when running vm/jvmti/ForceEarlyReturnObject/fero001/fero00103/fero00103.html JCK test on CPU with 47 cores. 
> 
> The crash happens at the time when test  code tries to check returned value and gets invalid oop.  Despite correct object was acquired by load_earlyret_value(), it is  accidentally substituted on the stack when remove_activation() is executed (see TemplateInterpreterGenerator::generate_earlyret_entry_for). Substitution, in turns, happens due to overlapping of expression and native stacks. Particularly esp equals to sp because frame with no expression is restored (that is correct).  
> 
> After that execution of following code sequence replaces TOS with  some irrelevant value. 
> 
> push(tos)  // -> puts value on expression stack
> unlock_object() // -> calls call_VM() and save registers on native stack, in fact, at the same place as esp
> pop(tos) // -> restores  invalid value
> 
> The fix restores expression stack to max possible for deoptimized method size.  Please consider if this fix covers the case workarounded by  [2] (I was not able to trace back and find the reason for this changeset). 
> 
> [1] http://cr.openjdk.java.net/~snazarki/earlyret_crash/
> [2] http://hg.openjdk.java.net/aarch64-port/jdk8u60/hotspot/file/83f5fdfd56ec/src/cpu/aarch64/vm/templateInterpreter_aarch64.cpp#l1909
I don't quite understand this.  If we are the top frame, then we must
allow space for max_stack, but in that case temps + extra_args is equal
to max_stack anyway, so we don't need to add max_stack to extra_args.
If we aren't the top frame, we peel back the native SP at the point of
call.

Can you tell me a bit more about this?

Andrew.



-- 
Andrew Haley
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
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