Re: [dpdk-dev] [PATCH 0/8] Improve build process

[Panu Matilainen <pmatilai@redhat.com>]

On 02/11/2015 01:11 PM, Gonzalez Monroy, Sergio wrote:
>> From: Neil Horman [mailto:nhorman@tuxdriver.com]
>> Sent: Friday, January 30, 2015 6:13 PM
>> To: Gonzalez Monroy, Sergio
>> Cc: Thomas Monjalon; dev@dpdk.org
>> Subject: Re: [dpdk-dev] [PATCH 0/8] Improve build process
>>
>> On Fri, Jan 30, 2015 at 05:38:49PM +0000, Gonzalez Monroy, Sergio wrote:
>
> [snip]
>
>>>
>>> So would it be reasonable to add DT_NEEDED entries to all DPDK libraries
>> but EAL?
>>> If I understood what you were saying right, we could enforce the
>>> 'dependency' in the linker script with something like this:
>>> $ cat  librte_eal.so
>>> INPUT( librte_eal.so.1 -lrte_mempool -lrte_malloc) We could have such
>>> linker script for librte_eal.so instead of the soft link once
>>> versioning is in place.
>>>
>> Correct.
>>
>>> Things that would be missing versus the proposed patch:
>>>   - As I have mention in previous post, ldd info for EAL library would not
>> reflect
>>>     its dependency to other DPDK libs.
>> librte_eal.so would no show those dependencies, as far as I know (though I
>> haven't explicitly checked).  The subordunate libraries included in the input
>> line, may or may not show dependencies among themselves, depending on
>> your build setup (and the use of --no-as-needed and -l when linking the
>> individual .so libraries.
>>
>>>   - I was enforcing resolving all references when building the libraries (-z
>> defs), so
>>>     we either remove it altogether or skip eal.
>> I think thats correct, yes.
>>
>>>   - All apps would show DT_NEEDED entries for a set of DPDK libraries that
>>>     in most cases are required (eal, mempool, malloc, mbuf, ring VS
>>> dpdk_core)
>>>
>> I think apps linked to libdpdk_core would have DT_NEEDED entries for
>> libdpdk_core, not the subordonate libraries (though check me on that to be
>> sure).
>>
> Just checked on this and they do link against the subordinate libraries, although
> It does not really matter as we are dropping the 'core' library approach anyway.
>
>>> I think that the linker script approach is reasonable if we prefer to
>>> go that way instead of creating a core library.
>>>
>> I think it would make sense from a build environment point of view, in that it
>> allows library specific flags to be incorporated properly.  I think the only
>> downside is that the individual libraries still need to be carried around
>> (though they can be ignored from an application build/run standpoint).
>> You're question should probably be asked of people using COMBINED_LIBS
>> currently to make sure that meets their needs, though I think it will.
>>
>> Neil
>>
> So I just realized that I was not having into account a possible scenario, where
> we have an app built with static dpdk libs then loading a dso with -d  option.
>
> In such case, because the pmd would have DT_NEEDED entries, dlopen will fail.
> So to enable such scenario we would need to build PMDs without DT_NEEDED
> entries.

Hmm, for that to be a problem you'd need to have the PMD built against 
shared dpdk libs and while the application is built against static dpdk 
libs. I dont think that's a supportable scenario in any case.

Or is there some other scenario that I'm not seeing?

	- Panu -