Re: [dpdk-dev] [PATCH] eal: don't use default library path for static binaries

[Bruce Richardson <bruce.richardson@intel.com>]

On Fri, Jun 26, 2020 at 10:05:42AM -0700, Stephen Hemminger wrote:
> On Fri, 26 Jun 2020 15:59:57 +0100
> Bruce Richardson <bruce.richardson@intel.com> wrote:
> 
> > When using statically linked DPDK binaries, the EAL checks the default PMD
> > path and tries to load any drivers there, despite the fact that all drivers
> > are normally linked into the binary.  This behaviour can cause issues if
> > the PMD path and lib dir is configured to a non-standard location which is
> > not in the ld.so.conf paths, e.g. a build with prefix set to a home
> > directory location. In a case such as this, EAL will try and
> > (unnecessarily) load the .so driver files but that load will fail as their
> > dependent libraries, such as ethdev, for example, will not be found.
> > 
> > Because of this, it is better if statically linked DPDK apps do not load
> > drivers from the standard paths automatically. The user can always have
> > this behaviour by explicitly specifying the path using -d flag, if so
> > desired.
> > 
> > Not loading the libraries automatically can also prevent potential issues
> > with a user building and running a statically-linked DPDK binary based off
> > a private copy of DPDK, while there exists on the same machine a
> > system-wide installation of DPDK in the default locations. Without this
> > change, the system-installed drivers will be loaded to the binary alongside
> > the statically-linked drivers, which is not what the user would have
> > intended.
> > 
> > To detect whether we are in a statically or dynamically linked binary, we
> > can have EAL try to get a dlopen handle to its own shared library, by
> > calling dlopen with the RTLD_NOLOAD flag. This will return NULL if there is
> > no such shared lib loaded i.e. the code is executing from a static library,
> > or a handle to the lib if it is loaded.
> > 
> > Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> 
> But what if the majority of the DPDK is statically linked but the
> application wants also load a dynamically linked driver?
> 
They use the -d flag as now. The only change here is that we don't
*automatically* (and silently) attempt to load all drivers from a system
location when you have a static binary.