RFR: JDK-8288003: log events for os::dll_unload [v3]

[Yasumasa Suenaga]

On Thu, 9 Jun 2022 15:35:27 GMT, Matthias Baesken <mbaesken at openjdk.org> wrote:

>> Currently we only log events for os::dll_load, but not for os::dll_unload, this patch adds it. On some platforms (Linux/Windows) we can use OS APIs (e.g. dlinfo on Linux) to log the path of the unloaded shared lib.
>
> Matthias Baesken has updated the pull request incrementally with one additional commit since the last revision:
> 
>   remove whitespace in os_linux.hpp

I think it is better to add null check to dll_unload() because it might be different behavior between Linux and Windows.

GetModuleFileName() on Windows will return the path of executable if NULL is passed to hModule.
https://docs.microsoft.com/ja-JP/windows/win32/api/libloaderapi/nf-libloaderapi-getmodulefilenamea

On the other hand, dlinfo() does not mention if NULL is passed in library handle.
https://man7.org/linux/man-pages/man3/dlinfo.3.html

I think dll_unload() is not expexted to unload executable...

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PR: https://git.openjdk.org/jdk/pull/9101