[asterisk-dev] [Code Review] 2797: optional_api: Fix linking problems between modules that export global symbols

[Tilghman Lesher]

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/branches/12/configure.ac
<https://reviewboard.asterisk.org/r/2797/#comment18673>

    At the same time, you could probably remove detection for the various types of weak symbol aliases, as this patch removes them.  No need to detect that which is unused.


- Tilghman Lesher


On Aug. 28, 2013, 8:29 p.m., David Lee wrote:
> 
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> This is an automatically generated e-mail. To reply, visit:
> https://reviewboard.asterisk.org/r/2797/
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> 
> (Updated Aug. 28, 2013, 8:29 p.m.)
> 
> 
> Review request for Asterisk Developers.
> 
> 
> Bugs: ASTERISK-22296
>     https://issues.asterisk.org/jira/browse/ASTERISK-22296
> 
> 
> Repository: Asterisk
> 
> 
> Description
> -------
> 
> With the new work in Asterisk 12, there are some uses of the
> optional_api that are prone to failure. The details are rather involved,
> and captured on [the wiki][1].
> 
> This patch addresses the issue by removing almost all of the magic from
> the optional API implementation. Instead of relying on weak symbol
> resolution, a new optional_api.c module was added to Asterisk core.
> 
> For modules providing an optional API, the pointer to the implementation
> function is registered with the core. For modules that use an optional
> API, a pointer to a stub function, along with a optional_ref function
> pointer are registered with the core. The optional_ref function pointers
> is set to the implementation function when it's provided, or the stub
> function when it's now.
> 
> Since the implementation no longer relies on magic, it is now supported
> on all platforms. In the spirit of choice, an OPTIONAL_API flag was
> added, so we can disable the optional_api if needed (maybe it's buggy on
> some bizarre platform I haven't tested on)
> 
> The AST_OPTIONAL_API*() macros themselves remained unchanged, so
> existing code could remain unchanged. But to help with debugging the
> optional_api, the patch limits the #include of optional API's to just
> the modules using the API. This also reduces resource waste maintaining
> optional_ref pointers that aren't used.
> 
> Other changes made as a part of this patch:
>  * The stubs for http_websocket that wrap system calls set errno to
>    ENOSYS.
> 
>  * res_http_websocket now properly increments module use count.
> 
>  * In loader.c, the while() wrappers around dlclose() were removed. The
>    while(!dlclose()) is actually an anti-pattern, which can lead to
>    infinite loops if the module you're attempting to unload exports a
>    symbol that was directly linked to.
> 
>  * The special handling of nonoptreq on systems without weak symbol
>    support was removed, since we no longer rely on weak symbols for
>    optional_api.
> 
>  [1]: https://wiki.asterisk.org/wiki/x/wACUAQ
> 
> 
> Diffs
> -----
> 
>   /branches/12/configure UNKNOWN 
>   /branches/12/channels/sip/include/sip.h 397673 
>   /branches/12/channels/chan_sip.c 397673 
>   /branches/12/build_tools/cflags.xml 397673 
>   /branches/12/CHANGES 397673 
>   /branches/12/configure.ac 397673 
>   /branches/12/include/asterisk/ari.h 397673 
>   /branches/12/include/asterisk/autoconfig.h.in 397673 
>   /branches/12/include/asterisk/compiler.h 397673 
>   /branches/12/include/asterisk/http_websocket.h 397673 
>   /branches/12/include/asterisk/optional_api.h 397673 
>   /branches/12/main/asterisk.c 397673 
>   /branches/12/main/loader.c 397673 
>   /branches/12/main/optional_api.c PRE-CREATION 
>   /branches/12/res/ari/ari_websockets.c 397673 
>   /branches/12/res/ari/internal.h 397673 
>   /branches/12/res/res_ari.c 397673 
>   /branches/12/res/res_ari_events.c 397673 
>   /branches/12/res/res_http_websocket.c 397673 
>   /branches/12/rest-api-templates/res_ari_resource.c.mustache 397673 
>   /branches/12/rest-api-templates/swagger_model.py 397673 
>   /branches/12/tests/test_optional_api.c PRE-CREATION 
> 
> Diff: https://reviewboard.asterisk.org/r/2797/diff/
> 
> 
> Testing
> -------
> 
> New optional_api tests pass.
> 
> The config below consistently fails when attempting to connect to the
> ARI WebSocket without this patch; consistently passes with this patch.
> 
> modules.conf:
>     [modules]
>     load => res_stasis.so
>     load => res_ari.so
>     load => res_ari_model.so
>     load => res_ari_events.so
>     load => res_http_websocket.so
> 
> http.conf:
>     [general]
>     enabled=yes
>     bindaddr=127.0.0.1
> 
> ari.conf:
>     [general]
>     enabled = yes
> 
>     [ari]
>     type = user
>     password = ari
> 
> 
> Thanks,
> 
> David Lee
> 
>

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