linux-kernel - Re: [PATCH 1/2] tools lib traceevent: Export dynamic symbols used by traceevent plugins

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Date:	Mon, 11 May 2015 16:33:09 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	He Kuang <hekuang@...wei.com>
Cc:	jolsa@...nel.org, a.p.zijlstra@...llo.nl, acme@...nel.org,
	mingo@...hat.com, wangnan0@...wei.com,
	linux-kernel@...r.kernel.org,
	Mathias Krause <minipli@...glemail.com>
Subject: Re: [PATCH 1/2] tools lib traceevent: Export dynamic symbols used by
 traceevent plugins

On Mon, May 11, 2015 at 09:35:26AM +0000, He Kuang wrote:
> Traceevent plugins need dynamic symbols exported from libtraceevent.a,
> otherwise a dlopen error will occur during plugins loading.
> 
> This patch uses dynamic-list-file to export dynamic symbols which will
> be used in plugins to perf executable.
> 
> The problem is covered up if feature-libpython is enabled, because
> PYTHON_EMBED_LDOPTS contains '-Xlinker --export-dynamic' which adds all
> symbols to the dynamic symbol table. So we should reproduce the problem
> by setting NO_LIBPYTHON=1.

there's was another patch taking the shortcut:
  http://marc.info/?l=linux-kernel&m=142885447432384&w=2

it seems it's not merged yet, but I like this one better

SNIP


> diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf
> index 03409cc..19c61e0 100644
> --- a/tools/perf/Makefile.perf
> +++ b/tools/perf/Makefile.perf
> @@ -172,6 +172,7 @@ endif
>  
>  LIBTRACEEVENT = $(TE_PATH)libtraceevent.a
>  export LIBTRACEEVENT
> +LIBTRACEEVENT_DYNAMIC_LIST = $(TE_PATH)libtraceevent-dynamic-list
>  
>  LIBAPI = $(LIB_PATH)libapi.a
>  export LIBAPI
> @@ -278,8 +279,9 @@ build := -f $(srctree)/tools/build/Makefile.build dir=. obj
>  $(PERF_IN): $(OUTPUT)PERF-VERSION-FILE $(OUTPUT)common-cmds.h FORCE
>  	$(Q)$(MAKE) $(build)=perf
>  
> -$(OUTPUT)perf: $(PERFLIBS) $(PERF_IN)
> -	$(QUIET_LINK)$(CC) $(CFLAGS) $(LDFLAGS) $(PERF_IN) $(LIBS) -o $@
> +LD_LIBTRACEEVENT_FLAGS += -Xlinker --dynamic-list=$(LIBTRACEEVENT_DYNAMIC_LIST)
> +$(OUTPUT)perf: $(PERFLIBS) $(PERF_IN) $(LIBTRACEEVENT_DYNAMIC_LIST)
> +	$(QUIET_LINK)$(CC) $(CFLAGS) $(LDFLAGS) $(LD_LIBTRACEEVENT_FLAGS) $(PERF_IN) $(LIBS) -o $@
>  
>  $(GTK_IN): FORCE
>  	$(Q)$(MAKE) $(build)=gtk
> @@ -375,6 +377,9 @@ LIBTRACEEVENT_FLAGS += plugin_dir=$(plugindir_SQ)
>  $(LIBTRACEEVENT): FORCE
>  	$(Q)$(MAKE) -C $(TRACE_EVENT_DIR) $(LIBTRACEEVENT_FLAGS) O=$(OUTPUT) $(OUTPUT)libtraceevent.a plugins
>  
> +$(LIBTRACEEVENT_DYNAMIC_LIST): $(LIBTRACEEVENT)
> +	$(Q)$(MAKE) -C $(TRACE_EVENT_DIR) $(LIBTRACEEVENT_FLAGS) O=$(OUTPUT) $(OUTPUT)libtraceevent-dynamic-list

hum, do we need extra target in Makefile.perf, it could be rebuilt any time
'plugins:' target in lib/tracevent/Makefile is called

jirka
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