RFR: 8253757: Add LLVM-based backend for hsdis

[monica beckwith]

Hi all,

I am on vacation right now, but we can take a look next week and see how we
can support the LLVM backend for hsdis. It is much required by
Windows-AArch64 and we would hate for all the good work to not make it
upstream.

Monica


Sent from my Arm powered smart device.

On Thu, Oct 14, 2021, 9:07 AM Andrew Haley <aph at openjdk.java.net> wrote:

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