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Hello, thank you for your post.
You can find the detailed commits log for the Amazon Linux kernel 5.10 branch in the public Github:
Note the build dates for the kernel versions in question:
# rpm -q --changelog kernel-5.10.155-138.670.amzn2 |head -1
* Wed Nov 23 2022 Builder <builder@amazon.com>
# rpm -q --changelog kernel-5.10.157-139.675.amzn2.x86_64 |head -1
* Thu Dec 08 2022 Builder <builder@amazon.com>
It is not clear if one of the commits between November 25 to December 8, 2022, was responsible for fixing the issue, or if it was the kernel build process. It is possible that the following commit for the btf_encoder may have fixed the issue:
https://github.com/acmel/dwarves/commit/58a98f76ac95b1bb11920ff2b58206b2364e6b3b
However, I was unable to determine with any certainty which version of the btf_encoder was involved in building the kernel.
If you continue to notice any issues with BTF info when using the latest kernel versions, please feel free to open a support case so we can review further.
Thanks SamM for the pointers. It seems it is indeed the kernel build process. I was able to reproduce with older dwarves which is responsible for creating the BTF info. I downloaded 5.10.29 source code, build the kernel with dwarves-1.17 and dwarves-1.22.
dwarves-1.17 did not generate the BTF info for "do_rename2" and dwarves-1.22 did generate. This tells me most likely the AL2 kernels <= 5.10.155 were built without the commit you pointed.
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Hello rshah, you are welcome. I am glad to see you took it a step further and verified the differences between building the kernel with dwarves-1.17 versus dwarves-1.22. Thank you for sharing your findings.
For additional context, I want to share a 3rd party blog post that investigates a similar issue in great depth, albeit this post focuses on a different function for which BTF info was missing in arm64 kernels: https://rhysre.net/how-an-obscure-arm64-link-option-broke-our-bpf-probe.html