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

[Stephen Hemminger <stephen@networkplumber.org>]

On Mon, 22 Jul 2019 10:06:11 +0100
Bruce Richardson <bruce.richardson@intel.com> wrote:

> 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.

The problem is that bus drivers register themselves in constructors and
these construtors are not run with as-needed.

One part of fixing this is:
diff --git a/mk/rte.app.mk b/mk/rte.app.mk
index df917f946497..46bdff8ec5e8 100644
--- a/mk/rte.app.mk
+++ b/mk/rte.app.mk
@@ -130,6 +130,9 @@ ifeq ($(CONFIG_RTE_LIBRTE_FSLMC_BUS),y)
 _LDLIBS-$(CONFIG_RTE_LIBRTE_COMMON_FSLMC)   += -lrte_common_fslmc
 endif
 
+# Bus devices register in constructor so always link
+_LDLIBS-y      += --no-as-needed
+
 _LDLIBS-$(CONFIG_RTE_LIBRTE_PCI_BUS)        += -lrte_bus_pci
 _LDLIBS-$(CONFIG_RTE_LIBRTE_VDEV_BUS)       += -lrte_bus_vdev
 _LDLIBS-$(CONFIG_RTE_LIBRTE_DPAA_BUS)       += -lrte_bus_dpaa
@@ -137,6 +140,8 @@ ifeq ($(CONFIG_RTE_EAL_VFIO),y)
 _LDLIBS-$(CONFIG_RTE_LIBRTE_FSLMC_BUS)      += -lrte_bus_fslmc
 endif
 
+_LDLIBS-y      += --as-needed
+
 ifeq ($(CONFIG_RTE_BUILD_SHARED_LIB),n)
 # plugins (link only if static libraries)