RFR(S) 8193318: ELF decoder should be able to use external debug info file

[Zhengyu Gu]

Hi Mikael,

On 03/14/2018 12:42 PM, Mikael Vidstedt wrote:
> 
>> On Mar 14, 2018, at 4:52 AM, coleen.phillimore at oracle.com wrote:
>>
>>
>> Hi, I looked at this and I really wasn't happy with all this extra code going into the JVM.  And I don't know this code.  There's a large hex table in this file:
>>
>> http://cr.openjdk.java.net/~zgu/8193318/webrev.00/src/hotspot/os/linux/decoder_linux.cpp.udiff.html <http://cr.openjdk.java.net/~zgu/8193318/webrev.00/src/hotspot/os/linux/decoder_linux.cpp.udiff.html>
> 
> I’m also curious - what is that code actually doing? Why is that hex table needed?

I should have added comment here, as Andrew did in SA implementation.

https://sourceware.org/gdb/current/onlinedocs/gdb/Separate-Debug-Files.html#Separate-Debug-Files

Thanks,

-Zhengyu

> 
> Cheers,
> Mikael
> 
>>
>> This seems like something that will be painful to maintain.  Can the SA be used for the cases where the binary is stripped?  I believe that Oracle ships with minimal stripping so that we have these symbols, why don't all suppliers?   I don't really like this change.
>>
>> Thanks,
>> Coleen
>>
>> On 3/8/18 11:12 AM, Zhengyu Gu wrote:
>>> Ping! I can get formal review?
>>>
>>> Thanks,
>>>
>>> -Zhengyu
>>>
>>>
>>> On 02/23/2018 12:26 PM, Zhengyu Gu wrote:
>>>> Thanks, Aleksey.
>>>>
>>>> On 02/23/2018 12:01 PM, Aleksey Shipilev wrote:
>>>>> On 02/15/2018 06:59 PM, Zhengyu Gu wrote:
>>>>>> This Linux only patch allows OpenJDK Linux distributions, which strip out debug symbols in
>>>>>> production bundles, to use external debuginfo bundles, if present, to decode stacks.
>>>>>>
>>>>>> The implementation mirrors SA implementation [1][2]. It has minimal impact to Oracle's JDK, which
>>>>>> always contains symbol tables.
>>>>>>
>>>>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8193318
>>>>>> Webrev: http://cr.openjdk.java.net/~zgu/8193318/webrev.00/
>>>>>
>>>>> Looks OK on my untrained eye.
>>>>>
>>>>> *) I am wondering if we can merge the existing implementation in
>>>>> src/jdk.hotspot.agent/linux/native/libsaproc/symtab.c and this mirror implementation in
>>>>> src/hotspot/os/linux/decoder_linux.cpp? Notably, moving gnu_debuglink_crc32 to some shared file
>>>>> would trim down the change.
>>>>
>>>> Yes, but I don't know if there is a way.
>>>>
>>>>>
>>>>> Andrew Haley knows this better, as he is the author of the related change.
>>>>
>>>> Cc'ed Andrew Haley.
>>>>
>>>> -Zhengyu
>>>>
>>>>
>>>>
>>>>>
>>>>> Thanks,
>>>>> -Aleksey
>>>>>
>>
>