Re: [dpdk-dev] [PATCH] pci: fix missing pci bus with shared library build

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

On Mon, Jul 22, 2019 at 09:38:27AM +0200, Thomas Monjalon wrote:
> 19/07/2019 22:55, Stephen Hemminger:
> > On Tue, 16 Jul 2019 09:46:04 +0100
> > Bruce Richardson <bruce.richardson@intel.com> wrote:
> > 
> > > On Mon, Jul 15, 2019 at 05:19:12PM -0700, Stephen Hemminger wrote:
> > > > On Mon, 15 Jul 2019 16:41:36 -0700
> > > > Stephen Hemminger <stephen@networkplumber.org> wrote:
> > > >   
> > > > > If DPDK is built as a shared library, then any application linked
> > > > > with rte.app.mk will not find any PCI devices. When the application
> > > > > is started no ethernet devices are found.
> > > > > 
> > > > > This is because the link order of libraries on the command line matters.
> > > > > And PCI is before EAL. That causes there to be no dependency on PCI
> > > > > so linker ignores linking the library. 
> > > > > Swapping the order fixes this.
> > > > > 
> > > > > Fixes: c752998b5e2e ("pci: introduce library and driver")
> > > > > Cc: stable@dpdk.org
> > > > > Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> > > > > ---
> > > > >  mk/rte.app.mk | 2 +-
> > > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > > > 
> > > > > diff --git a/mk/rte.app.mk b/mk/rte.app.mk
> > > > > index a277c808ed8e..470b92e4d73e 100644
> > > > > --- a/mk/rte.app.mk
> > > > > +++ b/mk/rte.app.mk
> > > > > @@ -90,8 +90,8 @@ _LDLIBS-$(CONFIG_RTE_LIBRTE_STACK)          += -lrte_stack
> > > > >  _LDLIBS-$(CONFIG_RTE_DRIVER_MEMPOOL_RING)   += -lrte_mempool_ring
> > > > >  _LDLIBS-$(CONFIG_RTE_LIBRTE_OCTEONTX2_MEMPOOL) += -lrte_mempool_octeontx2
> > > > >  _LDLIBS-$(CONFIG_RTE_LIBRTE_RING)           += -lrte_ring
> > > > > -_LDLIBS-$(CONFIG_RTE_LIBRTE_PCI)            += -lrte_pci
> > > > >  _LDLIBS-$(CONFIG_RTE_LIBRTE_EAL)            += -lrte_eal
> > > > > +_LDLIBS-$(CONFIG_RTE_LIBRTE_PCI)            += -lrte_pci
> > > > >  _LDLIBS-$(CONFIG_RTE_LIBRTE_CMDLINE)        += -lrte_cmdline
> > > > >  _LDLIBS-$(CONFIG_RTE_LIBRTE_REORDER)        += -lrte_reorder
> > > > >  _LDLIBS-$(CONFIG_RTE_LIBRTE_SCHED)          += -lrte_sched  
> > > > 
> > > > It still happens with 19.08. Testpmd works but only because it is
> > > > linked with so many things. But l3fwd fails...
> > > > 
> > > > # ./examples/l3fwd/build/l3fwd -n4 -l0-3 -w 02:00.0
> > > > EAL: Detected 8 lcore(s)
> > > > EAL: Detected 1 NUMA nodes
> > > > EAL: failed to parse device "02:00.0"
> > > > EAL: Unable to parse device '02:00.0'
> > > > EAL: Error - exiting with code: 1
> > > >   Cause: Invalid EAL parameters  
> > > 
> > > I don't think the position of these is going to be the cause here, the more
> > > likely cause is that the pci bus driver - and all other drivers - are not
> > > linked into apps for shared library builds. You always need to pass "-d"
> > > parameter to load drivers at init time (or have them installed in the
> > > correct driver path). For example, for me with a shared library build the
> > > following gives a no ports error:
> > > 
> > > 	sudo ./build/l2fwd -c F00000 -- -p 3
> > > 
> > > while this succeeds and runs fine
> > > 
> > > 	sudo ./build/l2fwd -c F00000 -d $RTE_SDK/$RTE_TARGET/lib/librte_pmd_i40e.so -- -p 3
> > 
> > The root cause is that recent gcc won't run constructor on unused libraries.
> > Testing a patch to take --as-needed off of PCI library.
> > 
> > See: https://stackoverflow.com/questions/11631161/force-to-link-against-unused-shared-library
> 
> The constructor is run when calling dlopen, right?
> 
> Note: dlopen with -d is a feature.
> The original idea was to be able to specify which driver we want to use.
> If we want an automatic dlopen, like modprobe, then we need more scripts.
> But I understand you are against the whole dlopen idea.
> 

This issue is more of a problem for development systems where we EAL path
is not really usable for finding the drivers. For a properly deployed
system where we use DPDK installed to /usr/local or /usr, the EAL PMD path
will be correctly configured and properly probe all drivers.