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List:       openjdk-hotspot-dev
Subject:    Re: AArch64: jtreg test vmTestbase/nsk/jvmti/PopFrame/popframe005 segfaults
From:       "Yangfei (Felix)" <felix.yang () huawei ! com>
Date:       2018-12-29 8:45:10
Message-ID: DA41BE1DDCA941489001C7FBD7A8820ED5F3C105 () dggeml527-mbx ! china ! huawei ! com
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Hi,

    The change looks good to me (NOT a Reviewer).  I think the aarch64 8u branches have the same issue.  

Thanks,
Felix


> 
> Hi,
> 
> Please review a one-line fix to prevent a JVMTI PopFrame crash on AArch64:
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8215951
> Webrev: http://cr.openjdk.java.net/~njian/8215951/webrev.0/
> 
> This jtreg test started intermittently failing on AArch64 with a
> segfault after 8215425:
>    http://hg.openjdk.java.net/jdk/jdk/rev/1e213c37befa
> (There is a full crash log attached to the bug.)
> 
> The faulting instruction is the load of the dispatch table pointer from
> rdispatch (x21) in InterpreterMacroAssembler::dispatch_base.
> 
>    0x0000ffff8c939ab8: ldrb   w8, [x22, #0]!
>    0x0000ffff8c939abc: add    w9, w8, #0x900
>    0x0000ffff8c939ac0: ldr    x9, [x21, w9, uxtw #3]   <------
>    0x0000ffff8c939ac4: br     x9
> 
> When deoptimising a frame that has a JVMTI PopFrame event pending,
> vframeArrayElement::unpack_on_stack will set the return PC of the
> deoptimised frame to the the interpreter entry point
> remove_activation_preserving_args_entry. After the PopFrame handling
> this calls dispatch_next to dispatch the next opcode, but at this point
> rdispatch may not have been initialised to point at the dispatch table.
> Fix by calling get_dispatch() to initialise rdispatch at the same time
> as the rest of the interpreter state is restored in
> remove_activation_preserving_args_entry.
> 
> I guess this has always been a potential problem, but adding the prints
> in the changeset above changed the timing of when a method was compiled
> and exposed it?
> 
> Thanks,
> Nick

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