bpf: inline test functions with ctx as input

[anfernee]

Run ebpf test on kernel v5.11 will raise the following error:

  Validating build_packet() func#1...
  btf_vmlinux is malformed
  Arg#0 type PTR in build_packet() is not supported yet.

It's due to missing kernel patch e5069b9c "bpf: Support pointers in global func args". Inline those functions so the ebpf test can also run on v5.11 and older kernels.

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[gentoo-root]

It's due to missing kernel patch e5069b9c "bpf: Support pointers in global func args".

This patch shouldn't be needed. As its commit message says, this patch adds support for pointer types different from PTR_TO_CTX, and PTR_TO_CTX used to be supported before. The pointer in scope of your commit is PTR_TO_CTX.

I believe the real root cause of the error you see is btf_vmlinux is malformed. When it happens, the verifier can't determine the type of the context pointer and treats struct __ctx_buff *ctx as PTR instead of PTR_TO_CTX.

Regarding btf_vmlinux is malformed, I'm not entirely sure why it happens, but a brief search hints that it might be because something was wrong with pahole or gcc during kernel compilation.

[anfernee]

Thanks for the quick reply!

It's due to missing kernel patch e5069b9c "bpf: Support pointers in global func args".

This patch shouldn't be needed. As its commit message says, this patch adds support for pointer types different from PTR_TO_CTX, and PTR_TO_CTX used to be supported before. The pointer in scope of your commit is PTR_TO_CTX.

I believe the real root cause of the error you see is btf_vmlinux is malformed. When it happens, the verifier can't determine the type of the context pointer and treats struct __ctx_buff *ctx as PTR instead of PTR_TO_CTX.

I see! This makes sense.

Regarding btf_vmlinux is malformed, I'm not entirely sure why it happens, but a brief search hints that it might be because something was wrong with pahole or gcc during kernel compilation.

I am also not sure why it happens, but inline the functions do fix the problem and make the test runnable on those kernels. Fixing Ubuntu kernel seem to the right approach, but considering it's not going to happen anytime soon. Do you think this patch can be accepted?

[pchaigno]

I think it's an acceptable change, but the rationale needs to be updated in the commit description as per Maxim's comment. Other than that, LGTM.

cc @dylandreimerink

[anfernee]

Thanks @pchaigno Re-worded the commit message.

[dylandreimerink]

I think it's an acceptable change

Yes, agreed. Making these function always inline should also improve support for older kernels without BPF-to-BPF support (not that we are currently running the suite on those versions).

[anfernee]

Thanks everyone!