linux-kernel - Re: [PATCH] perf: Ensure symbols for plugins are exported

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Message-ID: <20150417153430.GF17654@krava>
Date:	Fri, 17 Apr 2015 17:34:30 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Mathias Krause <minipli@...glemail.com>
Cc:	linux-kernel@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH] perf: Ensure symbols for plugins are exported

On Sun, Apr 12, 2015 at 06:00:51PM +0200, Mathias Krause wrote:
> When building perf with perl or python support it implicitly gets linked
> with the -export-dynamic linker option through the additional linker
> flags, namely with -Wl,-E via perl or -Xlinker -export-dynamic via
> python. That flag is essential for the traceevent plugin support so we
> shouldn't rely on adding it implicitly.
> 
> Ensure perf's exported symbols can be used by dlopen()ed plugins by
> unconditionally adding this flag when linking perf. Otherwise plugins
> won't be able to access symbols in the perf binary.
> 
> This fixes the following warning / bug when trying to load plugins:
> 
>   Warning: could not load plugin '/home/minipli/.traceevent/plugins/plugin_xen.so'
>   /home/minipli/.traceevent/plugins/plugin_xen.so: undefined symbol: trace_seq_printf
>   Warning: could not load plugin '/home/minipli/.traceevent/plugins/plugin_function.so'
>   /home/minipli/.traceevent/plugins/plugin_function.so: undefined symbol: warning
>   Warning: could not load plugin '/home/minipli/.traceevent/plugins/plugin_sched_switch.so'
>   /home/minipli/.traceevent/plugins/plugin_sched_switch.so: undefined symbol: pevent_unregister_event_handler
>   [...]

hum, not sure now how -export-dynamic works but should this
be rather in traceevent lib then?

jirka
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