Saint's Log

LLVM as an hsdis Backend

To specify a backend for hsdis, the OpenJDK repo needs to be configured with the --with-hsdis option. As of commit 77757ba9, LLVM is not yet supported as an hsdis disassembly backend. Therefore, this error from make/autoconf/jdk-options.m4 is displayed. Here’s an example on the Windows platform:

$ bash configure --with-hsdis=llvm
...
checking what hsdis backend to use... invalid
configure: error: Incorrect hsdis backend "llvm"
configure exiting with result code 1

There has been an effort to enable using LLVM as the hsdis disassembler’s backend. To use this change, check out this branch with those changes (and some conflict resolution to incorporate more recent changes).

hsdis LLVM backend on macOS ARM64

To test the LLVM backend for hsdis on macOS, install LLVM using brew (Apple’s LLVM does not have the llvm-c include files):

# install LLVM
brew install llvm

Now build the OpenJDK. This should use Apple’s compiler since we have not made any configuration changes.

cd ~/repos/java/jdk
bash configure
make images

Now add brew’s LLVM bin directory to the PATH and run bash configure again passing the --with-hsdis=llvm option as shown below. The configuration process will detect the clang++ compiler installed by brew and set it up for use when the build-hsdis target is executed.

# Now add brew's LLVM to the PATH before running bash configure
export OLDPATH=$PATH
export PATH="/opt/homebrew/opt/llvm/bin:$PATH"

bash configure --with-hsdis=llvm
make build-hsdis
make install-hsdis
export PATH=$OLDPATH

The install-hsdis target does not appear to be copying the hsdis library to the jdk/bin folder so these commands are required:

cd build/macosx-aarch64-server-release
cp support/hsdis/libhsdis.dylib jdk/bin/hsdis-aarch64.dylib

We can now test hsdis as described in the post about Building hsdis in Cygwin.

hsdis LLVM backend on Windows x86-64

To test the LLVM backend for hsdis, we need to first clone and builld LLVM because the LLVM installer does not come with the include files needed to build the changes in PR 5920. These instructions are from Jorn.

git clone https://github.com/llvm/llvm-project.git
cd llvm-project
mkdir build_llvm
cd build_llvm
cmake ../llvm -D"LLVM_TARGETS_TO_BUILD:STRING=X86" -D"CMAKE_BUILD_TYPE:STRING=Release" -D"CMAKE_INSTALL_PREFIX=install_local" -A x64 -T host=x64
cmake --build . --config Release --target install

Now we can configure the OpenJDK repo for hsdis, and build both the JDK and hsdis.

bash configure --with-hsdis=llvm \
     LLVM_CONFIG=C:/dev/repos/llvm-project/build_llvm/install_local/bin \
     --with-llvm=C:/dev/repos/llvm-project/build_llvm/install_local/
make build-hsdis
make images

hsdis LLVM backend on Windows ARM64

Open question: is this supported?

Testing the hsdis LLVM backend

The String.checkIndex method of PR 5920 is a good candidate for testing the hsdis LLVM backend. The -XX:CompileCommand option can be used to print the generated assembler code after compilation of the specified method.

java -XX:CompileCommand="print java.lang.String::checkIndex" -version

Tips

• To view the value of variables in GNU make, use the info control function, e.g. $(info Debug Info HSDIS_CFLAGS = $(HSDIS_CFLAGS))
• To view the command lines being executed by make as well as the value of the variables in use: make LOG=debug build-hsdis
• Autoconf macros are defined using the AC_DEFUN macro. The JDKOPT_SETUP_HSDIS macro (modified by PR 5920) is defined using AC_DEFUN_ONCE, which is for macros that should only be called once.
• To address warnings like ld: warning: dylib (/opt/homebrew/opt/llvm/lib/libunwind.dylib) was built for newer macOS version (12.0) than being linked (11.0) update MACOSX_VERSION_MIN in make/autoconf/flags.m4.