xdp_vlan01_kern.c:66:2: error: loop not unrolled: the optimizer was unable to perform the requested transformation; the transformation might be disabled or specified as part of an unsupported transformation ordering [-Werror,-Wpass-failed=transform-warning]

[NobinPegasus]

When I try to compile the codes the xdp_vlan01_kern.c uses #pragma unroll, it throws error.

    CC       xdp_prog_user
    CLANG    xdp_prog_kern_02.o
    LLC      xdp_prog_kern_02.o
    CLANG    xdp_prog_kern_03.o
    LLC      xdp_prog_kern_03.o
    CLANG    tc_reply_kern_02.o
    LLC      tc_reply_kern_02.o
    CLANG    xdp_vlan01_kern.o
xdp_vlan01_kern.c:66:2: error: loop not unrolled: the optimizer was unable to perform the requested transformation; the transformation might be disabled or specified as part of an unsupported transformation ordering [-Werror,-Wpass-failed=transform-warning]
   66 |         for (i = 0; i < VLAN_MAX_DEPTH; i++) {
      |         ^
1 error generated.
make: *** [../common/common.mk:116: xdp_vlan01_kern.o] Error 1

I'm using the latest clang

pegasus@pegasus:~/Documents/xdp-tutorial/packet-solutions$ clang --version
clang version 19.0.0git (https://github.com/llvm/llvm-project.git 815644b4dd882ade2e5649d4f97c3dd6f7aea200)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/pegasus/Documents/llvm-project/build/bin

[tohojo]

NobinPegasus ***@***.***> writes:

When I try to compile the codes the xdp_vlan01_kern.c uses #pragma unroll, it throws error. ``` CC xdp_prog_user CLANG xdp_prog_kern_02.o LLC xdp_prog_kern_02.o CLANG xdp_prog_kern_03.o LLC xdp_prog_kern_03.o CLANG tc_reply_kern_02.o LLC tc_reply_kern_02.o CLANG xdp_vlan01_kern.o xdp_vlan01_kern.c:66:2: error: loop not unrolled: the optimizer was unable to perform the requested transformation; the transformation might be disabled or specified as part of an unsupported transformation ordering [-Werror,-Wpass-failed=transform-warning] 66 | for (i = 0; i < VLAN_MAX_DEPTH; i++) { | ^ 1 error generated. make: *** [../common/common.mk:116: xdp_vlan01_kern.o] Error 1 ``` I'm using the latest clang ``` ***@***.***:~/Documents/xdp-tutorial/packet-solutions$ clang --version clang version 19.0.0git (https://github.com/llvm/llvm-project.git 815644b4dd882ade2e5649d4f97c3dd6f7aea200) Target: x86_64-unknown-linux-gnu Thread model: posix InstalledDir: /home/pegasus/Documents/llvm-project/build/bin ```

Hmm, this sounds like a regression in clang, then, so I would suggest reporting it to the LLVM developers...

[SailorStu]

Reducing VLAN_MAX_DEPTH from 10 to 2 (QinQ) is a workaround. Do we really need 10 of these iterations unrolled?

[tohojo]

Stuart Macdonald ***@***.***> writes:

Reducing VLAN_MAX_DEPTH from 10 to 2 (QinQ) is a workaround. Do we really need 10 of these iterations unrolled?

Hmm, maybe not; but it's still odd that this suddenly starts happening when it has worked fine before... :/

[Gloway17]

I also had this problem, but when I changed the clang version to 17, it was solved.

[huhager]

I face the same error using:

Ubuntu clang version 18.1.3 (1ubuntu1)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin

Workaround VLAN_MAX_DEPTH 2 compiles

[alexxdgfyuih8oyl76r5t4g]

I've got the same problem.
How to change VLAN_MAX_DEPTH?
googling did not help so far...

[John-Lin]

I've got the same problem. How to change VLAN_MAX_DEPTH? googling did not help so far...

edit this file in path packet-solutions/xdp_vlan01_kern.c and line 9
define VLAN_MAX_DEPTH 2

[bbczeuz]

Problem also exists on Ubuntu 24.04 using clang 18.1.3.
The whole code was introduced in c117051.
I wonder why they are trying to unroll this loop as it is recursively parsing the packet.
IMHO this could be dropped or reduced to lower values. e.g. my clang accepts

#define VLAN_MAX_DEPTH 8

@netoptimizer: What was the reasoning? Shall I open a PR? Why are you re-defining VLAN_MAX_DEPTH (common/parsing_helpers.h and packet-solutions/xdp_vlan01_kern.c)