Re: [dpdk-dev] [PATCH] devtools/test-meson-builds: allow custom set of examples

[Thomas Monjalon <thomas@monjalon.net>]

10/11/2020 11:08, Bruce Richardson:
> On Mon, Nov 09, 2020 at 08:26:10PM +0100, Thomas Monjalon wrote:
> > 09/11/2020 19:02, Bruce Richardson:
> > > On Mon, Nov 09, 2020 at 06:09:51PM +0100, Thomas Monjalon wrote:
> > > > 27/10/2020 18:38, Bruce Richardson:
> > > > > To test the installation process of DPDK using "ninja install"
> > > > > test-meson-builds.sh builds a subset of the examples using "make".
> > > > > To allow more flexibility for people testing, allow the set of
> > > > > examples chosen for this make test to be overridden using variable
> > > > > "DPDK_BUILD_TEST_EXAMPLES" in the environment.
> > > > > 
> > > > > Since a number of example apps link against drivers directly even
> > > > > for shared builds, we need to ensure that LD_LIBRARY_PATH points to
> > > > > the main DPDK lib folder so any dependencies of those drivers can
> > > > > be found e.g. that the PCI/vdev bus driver .so is found. [All
> > > > > drivers are symlinked from drivers dir back to lib dir on install,
> > > > > so only one dir rather than two is needed in the path.]
> > > > [...]
> > > > > +libdir=$(dirname $(find $DESTDIR -name librte_eal.so)) +export
> > > > > LD_LIBRARY_PATH=$libdir:$LD_LIBRARY_PATH
> > > > 
> > > > I don't get why libdir is required for some examples, and not for
> > > > others? The pkg-config file is not enough?
> > > > 
> > > 
> > > It's only needed for examples that link against drivers directly. 
> > > 
> > > I believe it's needed in those cases, because app linker flags
> > > (including e.g. -lrte_pmd_bond) occur before the pkg-config flags,
> > > which means that the linker at that point does not have the path to
> > > find the dependencies of the driver. [In a normal build, this wouldn't
> > > be necessary because the library directory would be a standard path]
> > 
> > If it's just a matter of ordering, it would be a better example to fix
> > the ordering in the Makefile, isn't it?
> > 
> 
> I thought about that, but it seems strange to have the DPDK linker flags
> appear before the application specific flags. The general style is to have
> the apps own linker flags apply first, and then the list of dependencies,
> so that any app linker flags take precedence. The other option is to have
> two separate LDFLAG variables for the app, one for before pkg-config flags
> and the other afterwards, but that is an untidy solution.
> 
> Therefore, I think it's better to keep the ordering in the examples as-is
> and just set the library path in the script. It's only a single extra
> assignment that is necessary because we are installing to a non-standard
> path using DESTDIR.

It is OK to add LD_LIBRARY_PATH in test-meson-builds.sh because
DPDK is "installed" with a DESTDIR prefix.

But this change is unrelated to test more examples,
it is a general fix for examples compilation.
The thing I'm missing, as I said above,
"why libdir is required for some examples, and not for others?"
I feel something wrong made linking work where it should not.