From mboxrd@z Thu Jan  1 00:00:00 1970
From: hollis_blanchard@mentor.com (Hollis Blanchard)
Date: Thu, 7 Jun 2012 14:26:22 -0700
Subject: [lttng-dev] -warn-common with lttng-ust 2.0.2
Message-ID: <4FD11C7E.7060303@mentor.com>

Hi, I was adding an LTTng UST 2.0 tracepoint to an application that uses 
-warn-common (see http://www.math.utah.edu/docs/info/ld_2.html). I 
created a simple tracepoint, had lttng-gen-tp produce tracepoints.o, 
then linked that to the application, along with -llttng-ust. This 
results in some warnings:

tracepoints.o: warning: common of `handle' overridden by definition
/usr/local/lib/liblttng-ust.so: warning: defined here
tracepoints.o: warning: common of `lttng_client_callbacks_overwrite' overridden by definition
/usr/local/lib/liblttng-ust.so: warning: defined here
tracepoints.o: warning: common of `lttng_client_callbacks_discard' overridden by definition
/usr/local/lib/liblttng-ust.so: warning: defined here
tracepoints.o: warning: common of `lttng_client_callbacks_metadata' overridden by definition
/usr/local/lib/liblttng-ust.so: warning: defined here
/usr/local/lib/liblttng-ust-tracepoint.so.0: warning: multiple common of `handle'
tracepoints.o: warning: previous common is here

This seems to be a valid warning. The LTTng UST headers contain 
definitions like this in include/lttng/ringbuffer-config.h:
struct lttng_ust_shm_handle *handle;

If two objects use that header, each will get a copy of "handle", right?

-- 
Hollis Blanchard
Mentor Graphics, Embedded Systems Division