RFR: 8371048: ImageFileReader::open fails to check return value of osSupport::map_memory

[Alan Bateman]

On Fri, 31 Oct 2025 14:00:38 GMT, Justin King <jcking at openjdk.org> wrote:

> Check whether `osSupport::map_memory` actually succeeded in all compliation modes, instead of crashing shortly after in non-debug builds. Ideally we should fall back to just reading the entire file into memory manually or use seek+read, but this is good enough for now to avoid crashing.

ClassLoader::setup_bootstrap_search_path_impl, and first use of ModuleFinder.ofSystem in early startup, attempt to stat lib/modules to determine if this is an images build. An images build is what jlink produces and always has a lib/modules file. When developers download a JDK it is an images build. In the JDK build itself there is an immediate "exploded" build but that isn't really used after the JDK is fully built. 

It would be good to exercise this code to see how VM startup behaves when JIMAGE_Open returns NULL. It's possible that the fastdebug build will trip on an assert early. For the exercise then it would be good to check both release and fastdebug builds.

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PR Comment: https://git.openjdk.org/jdk/pull/28087#issuecomment-3528098276