[dpdk-dev] [PATCH 1/1] eal: Don't fail secondary if primary is missing tailqs

[Burdick, Cliff]

-----Original Message-----
From: Thomas Monjalon [mailto:thomas at monjalon.net] 
Sent: Tuesday, November 13, 2018 8:07 AM
To: Burdick, Cliff
Cc: Burakov, Anatoly; dev at dpdk.org
Subject: Re: [dpdk-dev] [PATCH 1/1] eal: Don't fail secondary if primary is missing tailqs

13/11/2018 16:45, Burdick, Cliff:
> From: Burakov, Anatoly [mailto:anatoly.burakov at intel.com]
> > On 13-Nov-18 9:21 AM, Thomas Monjalon wrote:
> > > 13/11/2018 00:33, Burdick, Cliff:
> > >> This patch was submitted by Jean Tourrilhes over two years ago, 
> > >> but didn't receive any responses. I hit the same issue recently 
> > >> when trying to use cgo (Golang) as a primary process linked to 
> > >> libdpdk.a against a C++ application linked against the same 
> > >> library.> > >
> > > 
> > > The question is to know why you don't have the same constructors 
> > > in primary and seconday?
> > 
> > I've hit similar things in the past. I believe it was caused by our build system stripping out unused libraries (such as rte_hash) from the binary and thus not calling the constructor in the primary, but doing so in the secondary (or something to that effect).
> > In any case, this is caused by linking different number of libraries to primary and secondary, and should probably be fixed in the build system, not in the tailqs code (unless we specifically support having different linked libraries to primary and secondary?).
> 
> Right, I think the original author of the patch stated the reasons in the link I provided. The build system seems like the most appropriate place to fix it, but the patch got me going quickly. I think the question is whether you want DPDK to support these other ways of linking. I'm certainly not the first to use cgo, since there's a virtual switch project doing the same:
> 
> https://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_lagopu
> s_vsw&d=DwICAg&c=jcv3orpCsv7C4ly8-ubDoUfrxF5xIGWmptxGWP5vi5w&r=m1RLQOG
> Okz9MauvVLZmiGtyWc5mA7DejbPFNE1IDj-4&m=hQqVCNwW7eoEzB_hLFK97i8idS8FIqX
> oPeclwsIZq7Y&s=BMoBlwkqljwWIBY3SE3pPMCfVnOUlDuZLrno4-SojKM&e=
> 
> They don't use primary/secondary processes, though, so the issue is never hit. I'm in a situation where using cgo seemed like the easiest path to accomplish what I'm doing since I needed specialized libraries for it that were not available in C/C++. At some point I bet someone would use Cython to start linking against DPDK as well, and we'd likely run into the same issue.

>For sure, we want to support using DPDK with cgo or cython.
>But it is not clear what is the relation with not having the same compilation for primary and secondary. Please could you elaborate?

Hi Thomas, I think Jean explained it well here: https://dev.dpdk.narkive.com/ZM3a7QD1/dpdk-dev-bug-static-constructors-considered-evil

"The build system of the application does not have all the
subtelties of the DPDK build system, and ends up including *all* the
constructors, wether they are used or not in the code. Moreover, they
are included in a different order. Actually, by default the builds
include no constructors at all (which is a big fail), so the library
needs to be included with --whole-archive (see Snort DPDK
instructions)."

I will get to the bottom of my exact case to understand what's happening, but my primary application is a cgo application that I'm linking to by using almost exactly the same flags that are used in the DPDK build system to build examples. The DPDK libraries I'm linking against is a single location for both primary and secondary; in other words, I don't build DPDK twice. 

You had alluded to a pkg-config for DPDK in the 2015 thread, which cgo can use, but I don't know if that ever was implemented. Cgo can use pkg-config if it's available, otherwise the only tools are specifying LDFLAGS and CFLAGS into their build system.