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Facing an error while compiling for bpf using clang

Prashanth Fernando
 

Hi, 

I'm new to XDP, I am trying to compile a simple code to start with.
When I compile with clang, I face an error. Can someone please help me out in resolving this issue.

# clang -target bpf -c drop.c -o drop.o
error: unknown target triple 'bpf', please use -triple or -arch

OS: CentOS 7
Updated Kernel:
# uname -msr
Linux 5.1.3 x86_64

Built the kernel with the following flags on:
CONFIG_CGROUP_BPF=y
CONFIG_BPF=y
CONFIG_BPF_SYSCALL=y
CONFIG_BPF_JIT_ALWAYS_ON=y
CONFIG_NETFILTER_XT_MATCH_BPF=m
CONFIG_BPFILTER=y
CONFIG_BPFILTER_UMH=m
CONFIG_NET_CLS_BPF=m
CONFIG_NET_ACT_BPF=m
CONFIG_BPF_JIT=y
CONFIG_BPF_STREAM_PARSER=y
CONFIG_LWTUNNEL_BPF=y
CONFIG_HAVE_EBPF_JIT=y
CONFIG_BPF_EVENTS=y
CONFIG_BPF_KPROBE_OVERRIDE=y
CONFIG_TEST_BPF=m

I am not sure what I am missing still.

Tom Stellard
 

On 05/21/2019 08:42 PM, Prashanth Fernando wrote:
Hi,

I'm new to XDP, I am trying to compile a simple code to start with.
When I compile with clang, I face an error. Can someone please help me out in resolving this issue.

# clang -target bpf -c drop.c -o drop.o
error: unknown target triple 'bpf', please use -triple or -arch
Which version of clang are you using? It looks like it is missing the bpf
target.

-Tom

OS: CentOS 7
Updated Kernel:
# uname -msr
Linux 5.1.3 x86_64

Built the kernel with the following flags on:
CONFIG_CGROUP_BPF=y
CONFIG_BPF=y
CONFIG_BPF_SYSCALL=y
CONFIG_BPF_JIT_ALWAYS_ON=y
CONFIG_NETFILTER_XT_MATCH_BPF=m
CONFIG_BPFILTER=y
CONFIG_BPFILTER_UMH=m
CONFIG_NET_CLS_BPF=m
CONFIG_NET_ACT_BPF=m
CONFIG_BPF_JIT=y
CONFIG_BPF_STREAM_PARSER=y
CONFIG_LWTUNNEL_BPF=y
CONFIG_HAVE_EBPF_JIT=y
CONFIG_BPF_EVENTS=y
CONFIG_BPF_KPROBE_OVERRIDE=y
CONFIG_TEST_BPF=m

I am not sure what I am missing still.

Prashanth Fernando
 

Hi, 

The clang version I am using is 3.4.2

clang --version
clang version 3.4.2 (tags/RELEASE_34/dot2-final)
Target: x86_64-redhat-linux-gnu
Thread model: posix

Tks,
PRashanth 
 

Yonghong Song
 

bpf needs 3.7.1 and higher version. Later clang (>= 3.7.1) has more features.

On Tue, May 21, 2019 at 11:13 PM Prashanth Fernando
<prashanth.fernando@...> wrote:

Hi,

The clang version I am using is 3.4.2

clang --version
clang version 3.4.2 (tags/RELEASE_34/dot2-final)
Target: x86_64-redhat-linux-gnu
Thread model: posix

Tks,
PRashanth

Prashanth Fernando
 

Thank You, I updated clang and now I am able to compile the code in CentOS-7.

I am facing another issue while loading the ebpf code in tc. I am able to run this in Ubuntu-18.04, but the usecase is to run it in CentOS. Can someone please help me out in resolving it. 
replicator.o is my objext file and classifier/action are the classifier/action code.

# sudo tc filter add dev enp0s8 parent ffff: bpf obj replicator.o sec classifier flowid ffff:1 \
        action bpf obj replicator.o sec action ok
What is "obj"?
Usage: ... bpf ...
 
 [inline]:     run bytecode BPF_BYTECODE
 [from file]:  run bytecode-file FILE
 
               [ police POLICE_SPEC ] [ action ACTION_SPEC ]
               [ classid CLASSID ]
 
Where BPF_BYTECODE := 's,c t f k,c t f k,c t f k,...'
      c,t,f,k and s are decimals; s denotes number of 4-tuples
Where FILE points to a file containing the BPF_BYTECODE string

Tks,
PRashanth

Jesper Dangaard Brouer
 

On Tue, 21 May 2019 23:17:28 -0700
"Yonghong Song" <ys114321@...> wrote:

bpf needs 3.7.1 and higher version. Later clang (>= 3.7.1) has more features.
In the kernel tree it is documented here:
https://github.com/torvalds/linux/blob/master/samples/bpf/README.rst

But the kernel says:
clang >= version 3.4.0 + llvm >= version 3.7.1

What is your 'llc' version?
(run command: llc --version )



On Tue, May 21, 2019 at 11:13 PM Prashanth Fernando
<prashanth.fernando@...> wrote:

Hi,

The clang version I am using is 3.4.2

clang --version
clang version 3.4.2 (tags/RELEASE_34/dot2-final)
Target: x86_64-redhat-linux-gnu
Thread model: posix
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer

Jesper Dangaard Brouer
 

On Wed, 22 May 2019 00:26:54 -0700
"Prashanth Fernando" <prashanth.fernando@...> wrote:

Thank You, I updated clang and now I am able to compile the code in
CentOS-7.

I am facing another issue while loading the ebpf code in tc. I am
able to run this in Ubuntu-18.04, but the usecase is to run it in
CentOS. Can someone please help me out in resolving it.
You have to use CentOS-8 for TC (and XDP) support, or install a newer
kernel version on CentOS-7.

--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer

https://linuxhint.com/centos8-release-date-and-features/

Prashanth Fernando
 

Hi, 
Thanks for your response. I had a doubt that the kernel has to be upgraded.
So I upgraded the kernel to 5.1.3, still I face the issue. 

I compiled the kernel with these options, have I missed out some option ?

CONFIG_CGROUP_BPF=y
CONFIG_BPF=y
CONFIG_BPF_SYSCALL=y
CONFIG_BPF_JIT_ALWAYS_ON=y
CONFIG_NETFILTER_XT_MATCH_BPF=m
CONFIG_BPFILTER=y
CONFIG_BPFILTER_UMH=m
CONFIG_NET_CLS_BPF=m
CONFIG_NET_ACT_BPF=m
CONFIG_BPF_JIT=y
CONFIG_BPF_STREAM_PARSER=y
CONFIG_LWTUNNEL_BPF=y
CONFIG_HAVE_EBPF_JIT=y
CONFIG_BPF_EVENTS=y
CONFIG_BPF_KPROBE_OVERRIDE=y
CONFIG_TEST_BPF=m



[root@localhost linux-5.1.3]# uname -msr
Linux 5.1.3 x86_64
 

Toke Høiland-Jørgensen
 

Prashanth Fernando <prashanth.fernando@...> writes:

Hi,
Thanks for your response. I had a doubt that the kernel has to be upgraded.
So I upgraded the kernel to 5.1.3, still I face the issue.
You also need to compile a new version of iproute2 (where the 'tc' and
'ip' utilities come from).

-Toke

Daniel Borkmann
 

On 05/22/2019 09:26 AM, Prashanth Fernando wrote:
Thank You, I updated clang and now I am able to compile the code in CentOS-7.

I am facing another issue while loading the ebpf code in tc. I am able to run this in Ubuntu-18.04, but the usecase is to run it in CentOS. Can someone please help me out in resolving it.
replicator.o is my objext file and classifier/action are the classifier/action code.

# sudo tc filter add dev enp0s8 parent ffff: bpf obj replicator.o sec classifier flowid ffff:1 \
action bpf obj replicator.o sec action ok
What is "obj"?
Usage: ... bpf ...
Judging from above error and that it works on Ubuntu 18.04, then your iproute2
version in CentOS-7 is simply too old aka lacking eBPF support.

Try compiling one from recent Git [0] or some more recent tarball, then it
should work provided you have a proper kernel with it.

Perhaps also [1] might help you getting started, e.g. you can use cls_bpf in
direct action mode which is much more efficient than going through ac_bpf,
see the guide for more info.

[0] https://git.kernel.org/pub/scm/network/iproute2/iproute2.git/
[1] https://cilium.readthedocs.io/en/latest/bpf/#iproute2

[inline]:     run bytecode BPF_BYTECODE
[from file]:  run bytecode-file FILE

[ police POLICE_SPEC ] [ action ACTION_SPEC ]
[ classid CLASSID ]

Where BPF_BYTECODE := 's,c t f k,c t f k,c t f k,...'
c,t,f,k and s are decimals; s denotes number of 4-tuples
Where FILE points to a file containing the BPF_BYTECODE string

Tks,
PRashanth



Prashanth Fernando
 

Thank You Daniel for your timely help!