RFR: 8017234: Hotspot should stop using mapfiles

Thu Feb 22 09:57:54 UTC 2024

On Thu, 22 Feb 2024 00:29:55 GMT, David Holmes <dholmes at openjdk.org> wrote:

> My main concern with a change like this as that it likely has little effect on the OpenJDK itself, but we may be changing something that 3rd party applications linking with libjvm are relying on. I realize this is a bit "hand wavy" but are we sure this presents the exact same view of libjvm as before?

I realize that my essay-style comment was a bit TL;DR, but I tried to answer questions like this ahead of time in it. Let me quote:

> I have checked the resulting libjvm.so/jvm.dll using the COMPARE_BUILD functionality, which (among other things) analyzes differences between native libraries before and after a patch. This has verified that there is no change in the symbols of the Hotspot dynamic library on macOS/x64, macOS/aarch64 or Windows/x64. I have also gotten help from @MBaesken and @JoKern65 to confirmed that there is no effect on AIX.

On linux/x64 and linux/aarch64 there are some very minor changes:

> The difference is that the data (variable) symbols __bss_start, _edata and _end, and the text (function) symbols _fini and _init has changed from local to global. Afaik, these are symbols created by the linker. Also, when we used a mapfile, the symbol SUNWprivate_1.1 that was part of the mapfile definition was included in libjvm.so, and this is no longer the case.

So yes, I have worked hard to make sure the resulting libjvm.so/jvm.dll is as close as humanly possible before and after this PR. I cannot think of a way in which 3rd party applications could even spot the difference before and after this patch. (Except for a contrived counterexample like explicitly looking up the visibility of `_init` and checking that it is indeed local...)

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PR Comment: https://git.openjdk.org/jdk/pull/17955#issuecomment-1959081384