pahole creates BTF with lots of duplicate types

[Lorenz Bauer]

pahole 1.24-4ubuntu1 creates buggy BTF from vmlinux:

$ bpftool btf dump file 1.24-ubuntu.btf | grep "STRUCT 'net'" | wc -l
44

Upstream pahole from debian doesn't have this problem:

$ bpftool btf dump file 1.24-debian.btf | grep "STRUCT 'net'" | wc -l
1

This is also apparent in the created file sizes:

$ ls -lh *.btf
-rw-r-----. 1 lorenz lorenz 3.6M Jun 29 15:19 1.24.btf
-rw-r-----. 1 lorenz lorenz 3.6M Jun 29 15:26 1.24-debian.btf
-rw-r-----. 1 lorenz lorenz 8.5M Jun 29 15:16 1.24-ubuntu.btf

1.24.btf is created using pahole v1.24 built from source.

Looking at the Debian patch tracker, it seems like you are missing one patch: https://sources.debian.org/patches/dwarves/1.24-4.1/03-dwarves-Zero-initialize-struct-cu-in-cu__new-to-prev.patch/ vs https://git.launchpad.net/ubuntu/+source/dwarves/tree/debian/patches?h=applied/ubuntu/lunar

This causes problems in tools which use vmlinux BTF to do CO-RE relocations against the running kernel. On recent ubuntu kernels these are excruciatingly slow since your pahole creates bloated types.

[Dimitri John Ledkov (xnox)]

See https://bugs.launchpad.net/ubuntu/+source/dwarves/+bug/2025988

[Brian Murray (brian-murray)]

Ubuntu 23.04 (Lunar Lobster) has reached end of life, so this bug will not be fixed for that specific release.