Re: [PATCH bpf-next] selftests/bpf: add btf dedup test covering module BTF dedup

[Jiri Olsa <olsajiri@gmail.com>]

On Fri, Jun 20, 2025 at 03:34:14PM +0200, Jiri Olsa wrote:
> On Wed, Apr 30, 2025 at 02:42:49PM +0100, Alan Maguire wrote:
> > Recently issues were observed with module BTF deduplication failures
> > [1].  Add a dedup selftest that ensures that core kernel types are
> > referenced from split BTF as base BTF types.  To do this use bpf_testmod
> > functions which utilize core kernel types, specifically
> > 
> > ssize_t
> > bpf_testmod_test_write(struct file *file, struct kobject *kobj,
> >                        struct bin_attribute *bin_attr,
> >                        char *buf, loff_t off, size_t len);
> > 
> > __bpf_kfunc struct sock *bpf_kfunc_call_test3(struct sock *sk);
> > 
> > __bpf_kfunc void bpf_kfunc_call_test_pass_ctx(struct __sk_buff *skb);
> > 
> > For each of these ensure that the types they reference -
> > struct file, struct kobject, struct bin_attr etc - are in base BTF.
> > Note that because bpf_testmod.ko is built with distilled base BTF
> > the associated reference types - i.e. the PTR that points at a
> > "struct file" - will be in split BTF.  As a result the test resolves
> > typedef and pointer references and verifies the pointed-at or
> > typedef'ed type is in base BTF.  Because we use BTF from
> > /sys/kernel/btf/bpf_testmod relocation has occurred for the
> > referenced types and they will be base - not distilled base - types.
> > 
> > For large-scale dedup issues, we see such types appear in split BTF and
> > as a result this test fails.  Hence it is proposed as a test which will
> > fail when large-scale dedup issues have occurred.
> > 
> > [1] https://lore.kernel.org/dwarves/CAADnVQL+-LiJGXwxD3jEUrOonO-fX0SZC8496dVzUXvfkB7gYQ@mail.gmail.com/
> > 
> > Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
> 
> hi Alan,
> this one started to fail in my tests.. it's likely some screw up in
> my environment, but I haven't found the cause yet, I'm using the
> pahole 1.30 .. just cheking if it's known issue already ;-)

hum, it might be my gcc-14 .. will upgrade

jirka