From: Eduard Zingerman <eddyz87@gmail.com>
To: "Matthieu Baerts (NGI0)" <matttbe@kernel.org>,
ihor.solodrai@linux.dev, alan.maguire@oracle.com
Cc: bpf@vger.kernel.org, linux-kselftest@vger.kernel.org,
linux-kernel@vger.kernel.org, llvm@lists.linux.dev,
Andrii Nakryiko <andrii@kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Martin KaFai Lau <martin.lau@linux.dev>,
Song Liu <song@kernel.org>,
Yonghong Song <yonghong.song@linux.dev>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@kernel.org>,
Stanislav Fomichev <sdf@fomichev.me>,
Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>,
Shuah Khan <shuah@kernel.org>,
Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <nick.desaulniers+lkml@gmail.com>,
Bill Wendling <morbo@google.com>,
Justin Stitt <justinstitt@google.com>
Subject: Re: [PATCH bpf] selftests/bpf: fix implicit-function-declaration errors
Date: Fri, 03 Oct 2025 16:37:32 -0700 [thread overview]
Message-ID: <d108d59be611a63c73303347d07fe0ba5f2b74b7.camel@gmail.com> (raw)
In-Reply-To: <20251003-bpf-sft-fix-build-err-6-18-v1-1-2a71170861ef@kernel.org>
On Fri, 2025-10-03 at 17:24 +0200, Matthieu Baerts (NGI0) wrote:
> When trying to build the latest BPF selftests, with a debug kernel
> config, Pahole 1.30 and CLang 20.1.8 (and GCC 15.2), I got these errors:
>
> progs/dynptr_success.c:579:9: error: call to undeclared function 'bpf_dynptr_slice'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
> 579 | data = bpf_dynptr_slice(&ptr, 0, NULL, 1);
> | ^
> progs/dynptr_success.c:579:9: note: did you mean 'bpf_dynptr_size'?
> .virtme/build-debug-btf//tools/include/vmlinux.h:120280:14: note: 'bpf_dynptr_size' declared here
> 120280 | extern __u32 bpf_dynptr_size(const struct bpf_dynptr *p) __weak __ksym;
> | ^
> progs/dynptr_success.c:579:7: error: incompatible integer to pointer conversion assigning to '__u64 *' (aka 'unsigned long long *') from 'int' [-Wint-conversion]
> 579 | data = bpf_dynptr_slice(&ptr, 0, NULL, 1);
> | ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> progs/dynptr_success.c:596:9: error: call to undeclared function 'bpf_dynptr_slice'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
> 596 | data = bpf_dynptr_slice(&ptr, 0, NULL, 10);
> | ^
> progs/dynptr_success.c:596:7: error: incompatible integer to pointer conversion assigning to 'char *' from 'int' [-Wint-conversion]
> 596 | data = bpf_dynptr_slice(&ptr, 0, NULL, 10);
> | ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> I don't have these errors without the debug kernel config from
> kernel/configs/debug.config. With the debug kernel, bpf_dynptr_slice()
> is not declared in vmlinux.h. It is declared there without debug.config.
>
> The fix is similar to what is done in dynptr_fail.c which is also using
> bpf_dynptr_slice(): bpf_kfuncs.h is now included.
>
> Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
> ---
I can reproduce similar issue when including
kernel/configs/debug.config with my regular dev config, but for
different functions: bpf_rcu_read_{un,}lock().
However, this is not a way to fix this.
Kfuncs are not supposed to just disappear from DWARF.
Running pahole in verbose mode I see the following output:
$ pahole -V \
--btf_features=encode_force,var,float,enum64,decl_tag,type_tag,optimized_func,consistent_func,decl_tag_kfuncs \
--btf_features=attributes \
--lang_exclude=rust \
--btf_encode_detached=/dev/null vmlinux
...
matched function 'bpf_rcu_read_lock' with 'bpf_rcu_read_lock.cold'
...
Alan, Ihor, does this sound familiar?
next prev parent reply other threads:[~2025-10-03 23:37 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-10-03 15:24 [PATCH bpf] selftests/bpf: fix implicit-function-declaration errors Matthieu Baerts (NGI0)
2025-10-03 23:37 ` Eduard Zingerman [this message]
2025-10-04 3:08 ` Ihor Solodrai
2025-10-04 3:19 ` Ihor Solodrai
2025-10-04 8:52 ` Matthieu Baerts
2025-10-04 8:51 ` Matthieu Baerts
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