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Fix building jnidispatch with Android NDK 18+ using Clang/LLVM

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Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
20/100
Issue type
Bug
Clarity
Needs clarification
Activity status
Stale
Tech stack
android, c, java
Domain
build-system, mobile-dev

Research direction

Start by reviewing the proposed android-ndk-llvm branch and commit, then compare its build changes with the current jnidispatch build setup. Test the build with the supported Android NDK versions, including r27c, and establish whether the GCC-to-Clang transition works across the discussed targets.

Written by the indexing model from the issue text.

Description

More of a place for discussion than an urgent need to be resolved, I have specifically not made a PR yet as this is nowhere near comprehensively tested. It would be very helpful if anyone with libffi experience in other projects knows about any tricks moving from gcc to clang.

Anyway, here is a branch with my proposed changes: https://github.com/BugsBeGone/jna/commits/android-ndk-llvm/
Actual commit, which may be out of date if branch is rebased to sync with master: https://github.com/BugsBeGone/jna/commit/2be472422f4ea1c479ef1322253b9a1ab7d356e0

Some initial observations:

  • ARMv5 and MIPS (32 & 64) targets were removed in NDK r17. In theory the Play Store still supports versions of Android that could be running on those architectures, so it is a bit soon to drop them entirely if the old toolchains do still work. At the very least I would expect a major JNA version bump to indicate the removed targets (Edit: I guess those libs can always still be built with older NDKs, in which case no need for a breaking change by dropping support).

  • Standalone toolchains are a mess for detecting the version. I cannot think of a way that does not involve the user manually setting either the NDK major version, or a USE_CLANG define to work out which compiler suite to use. I would be in favour of officially not supporting the use of standalone toolchains, as you need approximately 1GB of extra disk space per target, so even testing it is a pain.

  • More to the point, NDKs between r17 & r21 generally seem to be unstable, requiring unholy combinations of GCC/Binutils & Clang/LLVM to work at all. Since the existing build environment has never worked with anything after r15, because of the switch to unified headers, we probably do not need to worry too much so long as everyone is happy to jump from let's say r15 to r22.

I have mostly been testing with NDK r27c, since that was the latest LTS release (Edit: r27d is still the latest LTS, the only differences from r27c are a couple of macOS-specific fixes).

Dominant language
Java
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Forks
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Avg merge
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Merged PRs (30d)
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