Re: [dpdk-users] Building a shared library that uses DPDK

[Jeffrey Helt <jhelt@andrew.cmu.edu>]

> On Feb 14, 2018, at 9:34 PM, Jeffrey Helt <jhelt@andrew.cmu.edu> wrote:
> 
> 
>> On Feb 14, 2018, at 8:08 PM, Stephen Hemminger <stephen@networkplumber.org> wrote:
>> 
>> On Wed, 14 Feb 2018 19:06:03 -0500
>> Jeffrey Helt <jhelt@andrew.cmu.edu> wrote:
>> 
>>> Hi,
>>> 
>>> I am attempting to build a shared library that uses DPDK, specifically that wraps the Linux socket API and backs it by shared memory DPDK shared memory regions. I built DPDK 17.11 with “CONFIG_RTE_BUILD_SHARED_LIB=y”. In my shared library directory, I am using the following Makefile:
>>> 
>>> ifeq ($(RTE_SDK),)
>>> $(error "Please define RTE_SDK environment variable")
>>> endif
>>> 
>>> # Default target, can be overridden by command line or environment
>>> RTE_TARGET ?= x86_64-native-linuxapp-gcc
>>> 
>>> include $(RTE_SDK)/mk/rte.vars.mk
>>> 
>>> # binary name
>>> SHARED = libshim.so
>>> 
>>> # all source are stored in SRCS-y
>>> SRCS-y := wrap_socket.c
>>> 
>>> CFLAGS += -O3
>>> 
>>> include $(RTE_SDK)/mk/rte.extshared.mk
>>> 
>>> However, whenever I try to use my library, such as with "LD_PRELOAD=./build/lib/libshim.so ./test”, I receive "symbol lookup error: ./build/lib/libshim.so: undefined symbol: rte_eal_init”. What am I missing?
>>> 
>>> Thank you in advance for help!
>>> 
>>> Jeff
>> The DPDK builds lots of little shared libraries.
>> You need to have all of them in your LD_LIBRARY_PATH and then add your socket wrapper.
> 
> Using `export LD_LIBRARY_PATH="/users/jhelt/dpdk/x86_64-native-linuxapp-gcc/lib/librte_eal.so”` before building and/or running doesn’t seem to change anything. Using ldd, I noticed that no dpdk shared objects are required by my library (see below), which seems like a more fundamental issue to me, although admittedly I am not that experienced in debugging linking issues.
> 
> $ ldd ./build/lib/libshim.so 
> 	linux-vdso.so.1 =>  (0x00007fff907e2000)
> 	libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007fe76b06a000)
> 	/lib64/ld-linux-x86-64.so.2 (0x00007fe76b636000) 
> 
> Jeff

I managed to solve this issue. For future reference for anyone facing a similar issue, I needed to update the Makefile to the following. Note the LDLIBS.  The "LDFLAGS += --no-undefined” was helpful in debugging missing symbols but is not required. After this change, I still needed to add the DPDK lib directory to my LD_LIBRARY_PATH as Stephen suggested.

Jeff

include $(RTE_SDK)/mk/rte.vars.mk

# binary name
SHARED = libshim.so

# all source are stored in SRCS-y
SRCS-y := wrap_socket.c

CFLAGS += -O3

LDFLAGS += --no-undefined
LDLIBS += -ldl -l:librte_eal.so

include $(RTE_SDK)/mk/rte.extshared.mk