On Thu, Nov 11, 2021 at 02:24:18AM IST, Vinicius Costa Gomes wrote:
> When CONFIG_DEBUG_INFO_BTF is enabled and CONFIG_BPF_SYSCALL is
> disabled, the following compilation error can be seen:
>
> GEN .version
> CHK include/generated/compile.h
> UPD include/generated/compile.h
> CC init/version.o
> AR init/built-in.a
> LD vmlinux.o
> MODPOST vmlinux.symvers
> MODINFO modules.builtin.modinfo
> GEN modules.builtin
> LD .tmp_vmlinux.btf
> ld: net/ipv4/tcp_cubic.o: in function `cubictcp_unregister':
> net/ipv4/tcp_cubic.c:545: undefined reference to `bpf_tcp_ca_kfunc_list'
> ld: net/ipv4/tcp_cubic.c:545: undefined reference to `unregister_kfunc_btf_id_set'
> ld: net/ipv4/tcp_cubic.o: in function `cubictcp_register':
> net/ipv4/tcp_cubic.c:539: undefined reference to `bpf_tcp_ca_kfunc_list'
> ld: net/ipv4/tcp_cubic.c:539: undefined reference to `register_kfunc_btf_id_set'
> BTF .btf.vmlinux.bin.o
> pahole: .tmp_vmlinux.btf: No such file or directory
> LD .tmp_vmlinux.kallsyms1
> .btf.vmlinux.bin.o: file not recognized: file format not recognized
> make: *** [Makefile:1187: vmlinux] Error 1
>
> 'bpf_tcp_ca_kfunc_list', 'register_kfunc_btf_id_set()' and
> 'unregister_kfunc_btf_id_set()' are only defined when
> CONFIG_BPF_SYSCALL is enabled.
>
> Fix that by moving those definitions somewhere that doesn't depend on
> the bpf() syscall.
>
> Fixes: 14f267d95fe4 ("bpf: btf: Introduce helpers for dynamic BTF set registration")
> Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@xxxxxxxxx>
Thanks for the fix.
But instead of moving this to core.c, you can probably make the btf.h
declaration conditional on CONFIG_BPF_SYSCALL, since this is not useful in
isolation (only used by verifier for module kfunc support). For the case of
kfunc_btf_id_list variables, just define it as an empty struct and static
variables, since the definition is still inside btf.c. So it becomes a noop for
!CONFIG_BPF_SYSCALL.
I am also not sure whether BTF is useful without BPF support, but maybe I'm
missing some usecase.
That's just my opinion however, I'll defer to BPF maintainers.
--
Kartikeya
