RFR: 8253757: Add LLVM-based backend for hsdis

[Xin Liu]

On Wed, 7 Oct 2020 00:48:24 GMT, Yasumasa Suenaga <ysuenaga at openjdk.org> wrote:

>> This is an interesting suggestion. There is a similar attempt at replacing binutils with capstone in
>> https://bugs.openjdk.java.net/browse/JDK-8188073, which unfortunately has not seen much progress due to lack of
>> resources; I don't know if you are aware of that? There is also a (extremely low priority) effort to rewrite the hsdis
>> makefile to be part of the normal build system, see e.g. https://bugs.openjdk.java.net/browse/JDK-8208495. Neither of
>> these should be any blocker for your change, but I think it might be good if you know about them.  I have couple of
>> concerns with your patch. One is the method in which LLVM is selected instead of binutils; afaict this depends on
>> having the `LLVM` variable set when executing the makefile. At the very least, this should be documented in the README.
>> I don't think any more complicated configuration is really necessary at this point.  With full integration with the
>> build system, a more user-friendly way of selecting hsdis backend should be implemented, though.  Second, and I don't
>> know if this is an artifact of git/github/the new skara tooling, but if you renamed hsdis.c to hsdis.cpp, this
>> relationship does not show up, not even in the generated webrevs. Instead they are considered a new + a deleted file.
>> This makes it hard to see what code changes you have done in that file.  And third; have you tested that your changes
>> (both changing the main file from C to C++, and any code changes in it) does not break the old binutils functionality?
>> Afaic there are no test suites for exercising hsdis :-( so manual ad-hoc testing is likely needed.
>
> Can you separate LLVM and binutils from hsdis.cpp?
> 
> I guess you say that the problem is both GCC and binutils are not available on Windows AArch64. Is it right?
> 1 question: binutils seems to support Windows AArch64. Did you try recently binutils? If we can use binutils on Windows
> AArch64, you can fix makefile only.
> https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=binutils/dlltool.c;h=ed016b97dc38cdb1b85d2f6df676b9c9750f0d41;hb=HEAD#l248

IMHO, it's great to have an alternative disassembler.  I personally had better experience using llvm MC when I decoded
aarch64 and AVX instructions than BFD.  Another argument is that LLVM toolchain is supposed to provide the premium
experience on non-gnu platforms such as FreeBSD.

@luhenry  I tried to build it with LLVM10.0.1
on my x86_64, ubuntu, I ran into a small problem. here is how I build.
`$make ARCH=amd64 CC=/opt/llvm/bin/clang CXX=/opt/llvm/bin/clang++ LLVM=/opt/llvm/`

I can't meet this condition because Makefile defines LIBOS_linux.
#elif defined(LIBOS_Linux) && defined(LIBARCH_amd64)
    return "x86_64-pc-linux-gnu";

Actually, Makefile assigns OS to windows/linux/aix/macosx (all lower case)and then
`CPPFLAGS    += -DLIBOS_$(OS) -DLIBOS="$(OS)" -DLIBARCH_$(LIBARCH) -DLIBARCH="$(LIBARCH)" -DLIB_EXT="$(LIB_EXT)"`

In hsdis.cpp, `native_target_triple` needs to match whatever Makefile defined.  With that fix, I generate llvm version
hsdis-amd64.so and it works flawlessly

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PR: https://git.openjdk.java.net/jdk/pull/392