Re: [dpdk-dev] [PATCH] mk: fix acl library static linking

[Sergio Gonzalez Monroy <sergio.gonzalez.monroy@intel.com>]

On 30/06/2016 16:28, Thomas Monjalon wrote:
> 2016-06-30 15:02, Sergio Gonzalez Monroy:
>> On 30/06/2016 13:44, Thomas Monjalon wrote:
>>> 2016-06-30 13:04, Sergio Gonzalez Monroy:
>>>> On 30/06/2016 12:38, Thomas Monjalon wrote:
>>>>> Does it need to be commented in rte.app.mk?
>>>>> The other libs are in whole-archive to support dlopen of drivers.
>>>>> But the problem here is not because of a driver use.
>>>> There seem to be a bunch of libraries under --whole-archive scope that
>>>> are not
>>>> PMDs, ie. cfgfile, cmdline...
>>>>
>>>> What is the criteria?
>>> The criteria is a bit vague. We must try to include only libs which can
>>> be used by a driver.
>>> cmdline should probably not be there.
>>> Does it make sense to use cfgfile in a driver? maybe yes.
>> So as it is, ACL autotest is broken when building static libs
>> (non-combined).
> I think the --whole-archive option must be set specifically for ACL
> with a comment explaining it is required because of weak functions:
>
> # librte_acl needs --whole-archive because of weak functions
> _LDLIBS-$(CONFIG_RTE_LIBRTE_ACL) += --whole-archive -lrte_acl --no-whole-archive

Will do.

>> For combined libs we usually wrap libdpdk.a with --whole-archive, thus it is
>> not an issue.
>>
>> Just thinking a bit more about the 'dlopen of drivers' case you
>> mentioned before,
>> shouldn't the driver have proper dependencies and therefore need shared
>> DPDK libraries?
> It is possible to build a .so, without any DT_NEEDED entries, which will
> find the required symbols in the static linked binary.

Of course! All DPDK libraries were like that until recently.
That doesn't mean it was right though.

>> What does happen if binary/app and driver are built against different
>> library versions?
> Bad things :)
>
>> Where does it say that we do support this use case?
> It is maybe not written. But I know it is used by people wanting to load
> some PMD.so on demand while having the rest statically compiled.
> I agree it needs to be documented and probably better managed and tested.
>

Note that this only applies to apps built with DPDK build system.

In my opinion, I don't think we should be supporting such case.
But if we were to, we are probably just better of whole-archiving all 
libraries into the
application. For example, what if there was a driver wanting to use ACL 
or any
other DPDK lib not currently in the set of libs we "consider" should be 
use by drivers?

Also, from what I have seen in the list, most folks do end up using 
combined lib and
wrapping it with --whole-archive.

Sergio