Re: [Qemu-devel] [PATCH] Create libqemutrace.a for all trace.o

[Paolo Bonzini]

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.