RFR(S): 8170548: VM may crash at startup because StdoutLog/StderrLog logging stream can be badly aligned

[Marcus Larsson]

On 12/01/2016 11:50 AM, Thomas Stüfe wrote:
> This is a good catch!
>
> I wonder why we could not just call the normal new() instead of placement
> new in LogFileStreamInitializer()? Is it because LogStdoutOutput is derived
> from CHeapObj, and we do not yet want to call os::malloc() ?

It was done with static memory because of concerns raised about leaking 
memory if loading & unloading the VM in a process [0].

Thanks,
Marcus

[0]: 
http://mail.openjdk.java.net/pipermail/hotspot-runtime-dev/2016-January/017662.html

>
> Thanks, Thomas
>
>
> On Thu, Dec 1, 2016 at 11:35 AM, Volker Simonis <volker.simonis at gmail.com>
> wrote:
>
>> Hi,
>>
>> can I please have a review and sponsor for the following fix:
>>
>> http://cr.openjdk.java.net/~simonis/webrevs/2016/8170548/
>> https://bugs.openjdk.java.net/browse/JDK-8170548
>>
>> Change "8146009: "pure virtual method called" with using new GC
>> logging mechanism" introduced a sophisticated initialization mechanism
>> for the logging stream. In order to avoid deconstruction of the
>> streams before the VM exits, it creates them with a placement new into
>> statically allocated memory:
>>
>> static bool initialized;
>> static char stdoutmem[sizeof(LogStdoutOutput)];
>> static char stderrmem[sizeof(LogStderrOutput)];
>>
>> LogStdoutOutput &StdoutLog = reinterpret_cast<
>> LogStdoutOutput&>(stdoutmem);
>> LogStderrOutput &StderrLog = reinterpret_cast<
>> LogStderrOutput&>(stderrmem);
>>
>> LogFileStreamInitializer::LogFileStreamInitializer() {
>>    if (!initialized) {
>>      ::new (&StdoutLog) LogStdoutOutput();
>>      ::new (&StderrLog) LogStderrOutput();
>>      initialized = true;
>>    }
>> }
>>
>> Unfortunately it is not guaranteed, that the static memory (which is a
>> char array) is well-aligned for the stream objects. Actually, the C++
>> standard only defines that it has to be at least 'char' aligned which
>> is obviously not enough for a stream object.
>> When building 'slowdebug' on Solaris with SS12u4 we indeed observed
>> reproducible crashes during VM initialization because of this issue.
>>
>> The fix is easy - just wrap the character arrays into unions to align
>> them appropriately.
>>
>> Thank you and best regards,
>> Volker
>>