RFR: 8271490: [ppc] [s390]: Crash in JavaThread::pd_get_top_frame_for_profiling

[Lutz Schmidt]

On Tue, 17 Aug 2021 03:37:25 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

>> Please review this pull request. It hardens the code on ppc and s390 against crashes while collecting stack traces for JFR. Stack frame collection in prims/forte.cpp will benefit from this fix as well as it uses the same platform-specific code.
>> 
>> Testing:
>> SAP-internal functional and stress testing. Verifying a positive effect is hard because the targeted crashes occur only very rarely. No negative side effects of the fix have been observed.
>
> src/hotspot/os_cpu/linux_s390/thread_linux_s390.cpp line 97:
> 
>> 95:       //  - ijava_state_unchecked() calculates it's result as
>> 96:       //      istate = fp() - z_ijava_state_size() = NULL - 0x68 DEBUG_ONLY(-8)
>> 97:       //  - istate->method dereferences memory at offset 8 from istate
> 
> I think a reference to the JBS issue would suffice as a comment here.

Years ago, I was told that direct references to JBS bugs in the code are strongly discouraged. On the other hand, I regard it as very important to have a detailed description available. So what to do? I need a second review anyway. Maybe she has a third opinion on that.

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PR: https://git.openjdk.java.net/jdk/pull/5071