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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>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/bpf/20250430134249.2451066-1-alan.maguire@oracle.com