RFR: 8253757: Add LLVM-based backend for hsdis

[Andrew Haley]

On Wed, 13 Oct 2021 07:26:21 GMT, Ludovic Henry <luhenry at openjdk.org> wrote:

>> This patch expands the newly added system for hsdis backends to include LLVM.
>> 
>> The actual code in hsdis-llvm.cpp is based heavily on the work by @luhenry, as published in the never integrated PR https://github.com/openjdk/jdk/pull/392. (I have basically just ripped out the binutils-based part of it.)
>> 
>> Unfortunately I have not been able to make this work properly on Windows. With some additional flags I made it compile without complaints, but it caused hotspot to segfault in `LoadLibrary` (!) in `os::dll_load` when I tried to load the library. This is somewhat ironic, since the initial implementation was created by Ludovic for the very purpose of using it on Windows.
>> 
>> The lack of Windows support in this patch does not mean it is impossible to get it to work, just that I need to co-operate with someone who has more experience of compiling LLVM on Windows, and/or are more eager to get this combination to work.
>
> Very happy to see it landing :) Thank you!
> 
> I don't have access to a windows machine, and even less a Windows-AArch64 machine. @lewurm would you be able to take a look?

> As for LLVM not giving you a good user experience; I can't really tell what's wrong. Apparently @luhenry (and @JornVernee I believe) has used this. I'm not really the target audience myself; I'm only trying to make it possible to use. If it is so severly limited as you say maybe this isn't worth pursuing. Some feedback from those who have tested it would be appeciated here, to help med understand if this patch should be dropped.

I don't think it should be dropped, but I imagine that the bugs can be fixed. If LLVM's disassembler always dies as soon as it sees something it can't recognize, I'm astonished. Maybe the LLVM I'm using is bad.

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PR: https://git.openjdk.java.net/jdk/pull/5920