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

[Zhengyu Gu]

>>>
>>>
>>> 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?
> If you look throught the code Zhengyu is patching it is used in
> gnu_debuglink_crc32 which gets called by verify_file_crc which is called
> from LinuxElfDebugInfo::by_debug_link which is called by
> ElfFile::load_debuginfo.
> 
> The point of calling verify_file_crc is to ensure that the crc stored in
> the Elf debuginfo file matches the calue computed from the file
> contents. The table is needed to do the crc computation.
> 
> The same table appears in the CRC intrinsic implementation in e.g. the
> AArch64 directory (look in stubRoutines_aarch64.cpp). I guess it is also
> in the equivalent x86 and sparc code. Hmm, looks like we now have an
> os-specific copy too!

Ah, I guess we have several copies of the same table.

Here is another one: jdk.hotspot.agent/linux/native/libsaproc/symtab.c

Any suggestions to consolidate them?

Thanks,

-Zhengyu

> 
> regards,
> 
> 
> Andrew Dinn
> -----------
> Senior Principal Software Engineer
> Red Hat UK Ltd
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