Some problems while linking the libraries

[kirazero17]

I seem to get undefined reference to objects in the bm_runtime namespace while building NS-3.39 with P4sim (with all examples).

This is only resolved after I copied libbmruntime.a from the behavioral model version 2 build artifact to /usr/local/lib, then create a pc file (I named it bmruntime.pc) in that directory with the following content:

prefix=/usr/local
exec_prefix=\${prefix}
libdir=\${exec_prefix}/lib
includedir=/usr/local/include/bm

Name: BMv2
Description: Behavioral Model
Version: 1.15.0
Libs: -L\${libdir} -lbmruntime
Cflags: -I\${includedir}

and added bmruntime and thrift to the third party libraries list in P4sim's CMakeLists.txt.

I dunno if anyone also encountered this behaviour ?

[Mingyumaz]

Thanks for reporting this issue.

This is related to the BMv2 library/linking path setup for p4sim. I am not fully sure whether it comes from the BMv2 installation path or pkg-config environment when installing the open-source P4 development tools following the p4lang tutorial, or from another local environment issue.

In my previous tests, I did not encounter this problem. After installing BMv2 correctly, the required BMv2 libraries should normally be available under /usr/local/lib/, and the corresponding header files should be under /usr/local/include/bm/.

You can also check the appendix in our VM environment documentation here. It shows the expected files and pkg-config entries in a normal installation. In particular, please check whether pkg-config can find the BMv2 package and whether the BMv2 libraries are correctly registered, for example:

pkg-config --list-all | grep -E "bm|simple_switch|boost_system"
pkg-config --cflags --libs bm
ls /usr/local/lib/ | grep bm
ls /usr/local/include/bm

If the BMv2 libraries exist but the linker still reports undefined references, then the issue is likely that the BMv2 library flags are not correctly passed to the ns-3/P4Sim build process.

[kirazero17]

Thanks for your response.

I am using the P4 VM from the tutorial (downloaded in Nov 2025), but earlier this year, I pulled the BMv2 code to a later version (I slightly modified a few .cpp files of BMv2 for more logs, but the build tools should be intact). Now I'm not sure if it was due to a change from the BMv2 devs or that I accidentally changed something myself. I may have a closer look into it in the future.

[Mingyumaz]

I think we have identified the root cause. The issue is not that bmruntime.pc is missing. Instead, the problem is that bmruntime.pc may exist and cause pkg-config/CMake to add -lbmruntime, but the actual library file libbmruntime.so or libbmruntime.a is not installed on the system. In BMv2, libbmruntime is marked as a non-installed library by autotools (noinst_), so it may only exist inside the BMv2 build tree and is not installed into /usr/local/lib.

This explains the linker error:

/usr/bin/ld: cannot find -lbmruntime

The correct fix is not to manually copy libbmruntime.a into /usr/local/lib. Instead, we should avoid referencing bmruntime at all.

libbmall is already pulled in through bm.pc, and it contains the required bm_runtime symbols. Therefore, linking against bm / libbmall is sufficient, and no separate bmruntime dependency is needed.

For PR #23, I think the solutions for modification, please update, and thanks for your help!