Java 21 Android 17 Termux Fix (experimental)

Experimental workaround for an OpenJDK 21 crash on Google Play Termux running Android 17 (ARM64).

Problem

Some OpenJDK 21 tools (javac, jimage) aborted with an Android ProtoLogNative JNI registration error. The investigation traced a transitive dependency through libandroid-shmem.so to Android framework libraries.

Proposed change

In upstream termux/libandroid-shmem, change the ashmem helper implementation:

• Replace ASharedMemory_create(name, size) with memfd_create(name, MFD_CLOEXEC) followed by ftruncate(fd, size) (close fd and preserve errno on failure).
• Replace ASharedMemory_getSize(fd) with fstat(fd, &st), checking st.st_size > INT32_MAX and setting errno = EOVERFLOW.
• Add #include <sys/stat.h>.
• Build without a direct dependency on libandroid.so.

Verified on one device

• Android 17, ARM64, Google Play Termux
• OpenJDK 21.0.11: java -version, javac -version, jimage --help, jlink --version
• javac Hello.java and java Hello completed successfully
• Gradle 9.6.0 --version
• Offline Gradle Java project: BUILD SUCCESSFUL (6 seconds)

Tests were performed using an isolated LD_LIBRARY_PATH override, without replacing the installed library.

Important limitations

Experimental, not a universal fix. Cross-process System V shared-memory semantics, API-level compatibility, and regression tests remain incomplete. Passing the above tests does not establish that the replacement is fully compatible with all users of libandroid-shmem.

Build (Termux)

Apply the changes to the upstream source, then run:

clang -D_GNU_SOURCE -fPIC -shared -std=c11 -Wall -Wextra \
  -Wl,--version-script=exports.txt \
  shmem.c -o libandroid-shmem-test.so -llog
readelf -d libandroid-shmem-test.so | grep NEEDED

Do not replace the system/Termux-installed shared library until compatibility has been reviewed.

Attribution and license

Derived from termux/libandroid-shmem. Original copyright and license terms are retained in LICENSE. This repository documents an experimental modification and test evidence; it is not an official Termux release.