On 10/3/25 4:37 PM, Eduard Zingerman wrote:
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?
This is most likely the issue addressed in this patch: https://lore.kernel.org/dwarves/f7553b3f-5827-4f50-81a9-9bd0802734b9@linux.d...
There wasn't a new pahole release with it yet.