[Bug dynamic-link/16805] dynamic library not getting reinitialized on multiple calls to dlopen()

["jason at redhat dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=16805

Jason Merrill <jason at redhat dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |jason at redhat dot com

--- Comment #4 from Jason Merrill <jason at redhat dot com> ---
(In reply to Dave Johansen from comment #2)
> From reading the comments on the gcc bugzilla and revision history of this
> change, it appears that it was made as an optimization to improve
> performance.

It's not an optimization, it's necessary for correctness in the situation where
you have

plugin A
  weak foo
plugin B
  weak foo
library C
  weak foo

and plugins A and B depend on library C.  When the program loads A with
RTLD_LOCAL, references to foo in A and C bind to the definition in A.  When the
program then loads B, references to foo in B bind to the definition in B, but
references to foo in C are still bound to the definition in A.  So if foo is a
variable, B and C are looking at different copies, leading to chaos.

Marking foo as STB_GNU_UNIQUE fixes this by making references in B resolve to
the definition in A.

I had suggested (in
https://www.sourceware.org/ml/libc-alpha/2002-05/msg00222.html) that references
in A and B should bind to the definition in C instead, but Ulrich rejected that
idea.

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