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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
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Tests to verify the following behavior of `btf_dedup_resolve_fwds`:
- remapping for struct forward declarations;
- remapping for union forward declarations;
- no remapping if forward declaration kind does not match similarly
named struct or union declaration;
- no remapping if forward declaration name is ambiguous;
- base ids are considered for fwd resolution in split btf scenario.
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Link: https://lore.kernel.org/bpf/20221109142611.879983-4-eddyz87@gmail.com
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The following warning is triggered when I used clang compiler
to build the selftest.
/.../prog_tests/btf_dedup_split.c:368:6: warning: variable 'btf2' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
if (!ASSERT_OK(err, "btf_dedup"))
^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/.../prog_tests/btf_dedup_split.c:424:12: note: uninitialized use occurs here
btf__free(btf2);
^~~~
/.../prog_tests/btf_dedup_split.c:368:2: note: remove the 'if' if its condition is always false
if (!ASSERT_OK(err, "btf_dedup"))
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/.../prog_tests/btf_dedup_split.c:343:25: note: initialize the variable 'btf2' to silence this warning
struct btf *btf1, *btf2;
^
= NULL
Initialize local variable btf2 = NULL and the warning is gone.
Fixes: 9a49afe6f5a5 ("selftests/bpf: Add btf_dedup case with duplicated structs within CU")
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20211209050403.1770836-1-yhs@fb.com
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We've added one extra patch that added back the use of legacy
btf__dedup() variant. Clean that up.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211201232824.3166325-5-andrii@kernel.org
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Add an artificial minimal example simulating compilers producing two
different types within a single CU that correspond to identical struct
definitions.
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20211117194114.347675-2-andrii@kernel.org
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btf__dedup() and struct btf_dedup_opts were added before we figured out
OPTS mechanism. As such, btf_dedup_opts is non-extensible without
breaking an ABI and potentially crashing user application.
Unfortunately, btf__dedup() and btf_dedup_opts are short and succinct
names that would be great to preserve and use going forward. So we use
___libbpf_override() macro approach, used previously for bpf_prog_load()
API, to define a new btf__dedup() variant that accepts only struct btf *
and struct btf_dedup_opts * arguments, and rename the old btf__dedup()
implementation into btf__dedup_deprecated(). This keeps both source and
binary compatibility with old and new applications.
The biggest problem was struct btf_dedup_opts, which wasn't OPTS-based,
and as such doesn't have `size_t sz;` as a first field. But btf__dedup()
is a pretty rarely used API and I believe that the only currently known
users (besides selftests) are libbpf's own bpf_linker and pahole.
Neither use case actually uses options and just passes NULL. So instead
of doing extra hacks, just rewrite struct btf_dedup_opts into OPTS-based
one, move btf_ext argument into those opts (only bpf_linker needs to
dedup btf_ext, so it's not a typical thing to specify), and drop never
used `dont_resolve_fwds` option (it was never used anywhere, AFAIK, it
makes BTF dedup much less useful and efficient).
Just in case, for old implementation, btf__dedup_deprecated(), detect
non-NULL options and error out with helpful message, to help users
migrate, if there are any user playing with btf__dedup().
The last remaining piece is dedup_table_size, which is another
anachronism from very early days of BTF dedup. Since then it has been
reduced to the only valid value, 1, to request forced hash collisions.
This is only used during testing. So instead introduce a bool flag to
force collisions explicitly.
This patch also adapts selftests to new btf__dedup() and btf_dedup_opts
use to avoid selftests breakage.
[0] Closes: https://github.com/libbpf/libbpf/issues/281
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211111053624.190580-4-andrii@kernel.org
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Add selftests validating BTF deduplication for split BTF case. Add a helper
macro that allows to validate entire BTF with raw BTF dump, not just
type-by-type. This saves tons of code and complexity.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20201105043402.2530976-11-andrii@kernel.org
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