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From: Paolo Bonzini <pbonzini@redhat.com>
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Date: Tue, 28 Mar 2017 09:57:09 +0200
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Subject: Re: [Qemu-devel] [PATCH] Create libqemutrace.a for all trace.o
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To: "Xu, Anthony" <anthony.xu@intel.com>, Stefan Hajnoczi <stefanha@gmail.com>
Cc: "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, Daniel Berrange <berrange@redhat.com>



On 27/03/2017 20:21, Xu, Anthony wrote:
>>> ./trace.o, ./qapi/trace.o and ./util/trace.o are added into
>>> libqemuutil.a  to avoid recursive dependencies between
>>> libqemuutil.a and libqemutrace.a.
>> Why would libqemutrace.a depend on libqemuutil.a?
> Each trace.c calls trace_event_register_group to register events, 
> trace_event_register_group is defined in trace/control.c , which 
> is linked into libqemuutil.a.

Ah:

util-obj-$(CONFIG_TRACE_SIMPLE) += simple.o
util-obj-$(CONFIG_TRACE_FTRACE) += ftrace.o
util-obj-y += control.o
util-obj-y += qmp.o

With the introduction of libqemutrace.a, I believe these should be moved
into libqemutrace.a.

Paolo

> 
>> Tracing code shouldn't call other QEMU code.  That would could create
>> infinite recursion when a trace event is fired.
> If all trace.o needed by libqemuutil.a are linked into libqemuutil.a, 
> libqemuutil.a will not depend on libqemutrace.a. This is what this patch 
> take to break the infinite recursion.
> 
> Or we can link trace/*.o to libqemutrace.a, hope it breaks the infinite 
> recursion. But trace/*.o may still depend on libqemuutil.a
> 
> Or we can just link all trace.o to libqemuutil.a.