RFR: 8349638: Build libjdwp with SIZE optimization

[Chris Plummer]

On Mon, 24 Feb 2025 12:39:37 GMT, Matthias Baesken <mbaesken at openjdk.org> wrote:

> To be sure, I did a minimal build on Linux x86_64. I set `--with-jvm-features=minimal --with-jvm-variants=minimal` for this.
> This leads to
> `JVM_FEATURES_minimal='compiler1 minimal opt-size serialgc'`
> So no jvmti, to GCs except serialgc . Just C1, no C2. The 'opt-size' flag is set so the libjvm is compiled with size optimization (on Linux -Os). The other native libs (JDK native libs) still use the opt-flags they always use, as I thought.

"minimal" if a very specific footprint reducing build configuration. However, I believe what it does is enable a bunch of other individual footprint reduction features. For example, even without configuring specifically for minimal, you can optionally exclude JVMTI, or extra GCs, or C2, and I think you can optionally configure libjvm.so to be built for small size, not performance. It's not "all or none", but we don't really encourage (or officially support) selectively choosing what to exclude because it is not well tested.

> On the other hand we can achieve good performance and smaller binaries with lto (at least with gcc).

Absence of benchmarking and given the relatively small footprint savings, I don't think we should switch to SIZE. LTO seems fine. I don't know of any negative impacts with using it.

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PR Comment: https://git.openjdk.org/jdk/pull/23563#issuecomment-2680236696