Re: [dpdk-dev] [PATCH v2 1/4] mk: Remove combined library and related options

[Thomas Monjalon <thomas.monjalon@6wind.com>]

Hi Sergio,

Thank you for explaining the situation.

2015-03-18 12:11, Gonzalez Monroy, Sergio:
> Given that the patch to remove combined libraries is not welcome, I'll 
> try to explain the current situation so we can agree on the way forward.
> 
> Currently we have build config option for shared libraries and combined 
> libraries. Thus, this results in four possible combinations when 
> building dpdk:
> - not combined static
> - not combined shared
> - combined static
> - combined shared
> 
> The makefile rules/targets for combined are different than for not 
> combined. Thus, we currently have two different files for 
> archive/linking (rte.lib.mk and rte.sharelib.mk).
> 
> Since having versioning, combined shared libraries build will be broken 
> the moment we add a versioned API, as we do not have a global version 
> map that we use when linking such library.
> Also in my opinion, we would want to prevent users linking against a 
> combined libdpdk.so that may have different features built-in, with the 
> corresponding debugging difficulties when users
> report different problems/errors. I think this would defeat many of the 
> advantages of using shared libraries.
> 
> By removing the combined library build option, we would simplify the 
> build system with only two possible choices:
> - static
> - shared

+1
I believe that simplification is the way go.

> This would allow us to remove one file (rte.sharelib.mk) and have a 
> single file with archive/linking rules.
> 
> For the convenience of linking against a single library instead of the 
> multiple dpdk libraries, there are a few ways to go around it:
>   - for combined static lib, we can either have a script to re-archive 
> all libraries into a single/combined library (ie. extract all archives 
> into one directory, the re-archive all objects into a combined library),
>    or use a linker script (ie. GROUP ( -lrte_eal -lrte_malloc ... ) ).
> - for combined shared lib, we can use a linker script (ie. INPUT ( 
> -lrte_eal -lrte_malloc ... AS_NEEDED -lrte_hash ...) ) or we could use a 
> global version map (either somehow merging all independent version maps
> or maintaining a global version map).
> 
> My preference would be to remove the combined libs as a build config 
> option, then either add scripts to create those linker scripts or 
> document it so users know how to create their own linker scripts.
> This would simplify the build process and still be able to provide the 
> convenience of the combined library by using a linker script.
> 
> Comments?

You're right about the word convenience.
There are many ways to provide such convenience.
The first one is to simply use the DPDK makefiles which abstract linking problems.
If using DPDK framework is not an option, we can add new conveniences like
scripts or pkgconfig support.