[dpdk-users] dpdk-20.11 and shared libraries

[Templin (US), Fred L]

Hi, as an example of where I am having trouble with shared libraries, I am
trying to modify the "helloworld" example program so that I can invoke it
as: "helloworld --vdev net_null0". Working by looking at the low-level
dpdk-20.11 driver code, I tried adding a call to "rte_vdev_init()" to the
helloworld main.c as shown in the code diffs below. When I tried to
build (as shared), I got an error from the loader saying the reference
to 'rte_vdev_init' is undefined.

Am I even barking up the right tree?

Fred

--- main.c	2021-04-20 08:17:37.895698070 -0700
+++ main.c.net_null	2021-04-20 08:24:51.958198682 -0700
@@ -14,6 +14,9 @@
 #include <rte_per_lcore.h>
 #include <rte_lcore.h>
 #include <rte_debug.h>
+#if 1
+#include <rte_bus_vdev.h>
+#endif
 
 static int
 lcore_hello(__rte_unused void *arg)
@@ -30,6 +33,12 @@
 	int ret;
 	unsigned lcore_id;
 
+#if 1
+	ret = rte_vdev_init("net_null", NULL);
+	if (ret < 0)
+		rte_panic("Cannot init net_null\n");
+#endif
+
 	ret = rte_eal_init(argc, argv);
 	if (ret < 0)
 		rte_panic("Cannot init EAL\n");

cc -O3 -include rte_config.h -march=native -I/usr/local/include -DALLOW_EXPERIMENTAL_API main.c -o build/helloworld-shared  -L/usr/local/lib/x86_64-linux-gnu -Wl,--as-needed -lrte_node -lrte_graph -lrte_bpf -lrte_flow_classify -lrte_pipeline -lrte_table -lrte_port -lrte_fib -lrte_ipsec -lrte_vhost -lrte_stack -lrte_security -lrte_sched -lrte_reorder -lrte_rib -lrte_regexdev -lrte_rawdev -lrte_pdump -lrte_power -lrte_member -lrte_lpm -lrte_latencystats -lrte_kni -lrte_jobstats -lrte_ip_frag -lrte_gso -lrte_gro -lrte_eventdev -lrte_efd -lrte_distributor -lrte_cryptodev -lrte_compressdev -lrte_cfgfile -lrte_bitratestats -lrte_bbdev -lrte_acl -lrte_timer -lrte_hash -lrte_metrics -lrte_cmdline -lrte_pci -lrte_ethdev -lrte_meter -lrte_net -lrte_mbuf -lrte_mempool -lrte_rcu -lrte_ring -lrte_eal -lrte_telemetry -lrte_kvargs
/tmp/ccgU3Rpi.o: In function `main':
main.c:(.text.startup+0x15): undefined reference to `rte_vdev_init'
collect2: error: ld returned 1 exit status
Makefile:32: recipe for target 'build/helloworld-shared' failed
make: *** [build/helloworld-shared] Error 1

> -----Original Message-----
> From: users [mailto:users-bounces at dpdk.org] On Behalf Of Templin (US), Fred L
> Sent: Tuesday, April 20, 2021 9:25 AM
> To: users at dpdk.org; Stephen Hemminger <stephen at networkplumber.org>
> Subject: [dpdk-users] dpdk-20.11 and shared libraries
> 
> Hi, I have put a lot of time into learning about dpdk-20.11 but I have not yet found
> documentation on how to use it with shared libraries.  In dpdk-20.11, the examples
> are all built as "static" by default meaning that the entire kitchen sink of all DPDK
> libraries are linked in during the "ld" phase and the resulting binary is huge. When
> built as "static", the examples all appear to work fine as everything is loaded by
> default at runtime.
> 
> When I build the examples as "shared", however, the story is completely different.
> Examples that run fine as "static" do not work at all when built as "shared". It is
> clear that somehow the build procedure is not giving adequate instructions to the
> loader so that all necessary libraries will be ready to go at runtime.
> 
> I believe what needs to happen is that initialization code needs to be added to the
> example "main.c" modules to initialize functions that will be needed by lower levels
> but that are not being picked up on by the loader. But, I can find no documentation
> for how to do this. In my next message, I will send a code example of what I have
> tried so far.
> 
> Stephen, can you provide guidance on how to work with dpdk-20.11 in shared
> library environments? I would be happy to be pointed to any documentation
> I may be missing.
> 
> Thanks - Fred
>