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) <[email protected]>
>> ---
>
> 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/[email protected]/
There wasn't a new pahole release with it yet.
