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From "Andy Isaacson (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3742) libhdfs symbol visibility issues
Date Tue, 31 Jul 2012 00:21:34 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3742?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13425416#comment-13425416

Andy Isaacson commented on HDFS-3742:

bq. exported globals is less efficient than those that aren't exported.

I'm not convinced that that effect is even real (I'd want to see a fully worked example showing
improved codegen) but even if it is, we're talking about a few dozen instructions at most,
some PIC reloads and maybe a PLT fixup or 10, in the context of a JNI implementation. Worrying
about the PLT here is several orders of magnitude below the level of optimization that makes
sense in this context.

bq. don't think new contributors will understand how to add new functions

If we use a linker script with default hidden visibility, the new function won't work until
they grep the source tree for a function that does work and then do the same thing for their
new function.  This is not hard.  Version scripts are not black magic anymore, it's 2012 not
> libhdfs symbol visibility issues
> --------------------------------
>                 Key: HDFS-3742
>                 URL: https://issues.apache.org/jira/browse/HDFS-3742
>             Project: Hadoop HDFS
>          Issue Type: Bug
>    Affects Versions: 2.2.0-alpha
>            Reporter: Colin Patrick McCabe
>            Assignee: Colin Patrick McCabe
>            Priority: Minor
> libhdfs symbols should be hidden unless they're part of the API.  If we don't hide symbols,
they could conflict with symbols in a library user's program.
> This can be accomplished with __attribute__((visibility)) like this:
> {code}
> void __attribute__((visibility("hidden"))) bar(int i);
> {code}

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