On 8/16/23 8:48 PM, Alexei Starovoitov wrote:
On Wed, Aug 16, 2023 at 8:38 PM Yonghong Song <yonghong.song@xxxxxxxxx> wrote:
On 8/16/23 8:06 AM, David Vernet wrote:
We recently got an lkp warning about missing declarations, as in e.g.
[0]. This warning is largely redundant with -Wmissing-prototypes, which
we already disable for kfuncs that have global linkage and are meant to
be exported in BTF, and called from BPF programs. Let's also disable
-Wmissing-declarations for kfuncs. For what it's worth, I wasn't able to
reproduce the warning even on W <= 3, so I can't actually be 100% sure
this fixes the issue.
[0]: https://lore.kernel.org/all/202308162115.Hn23vv3n-lkp@xxxxxxxxx/
Okay, I just got a similar email to [0] which complains
bpf_obj_new_impl, ..., bpf_cast_to_kern_ctx
missing declarations.
In the email, the used compiler is
compiler: gcc-7 (Ubuntu 7.5.0-6ubuntu2) 7.5.0
Unfortunately, I did not have gcc-7 to verify this.
Also, what is the minimum gcc version kernel supports? 5.1?
pahole and BTF might be broken in such old GCC too.
Maybe we should add:
config BPF_SYSCALL
depends on GCC_VERSION >= 90000 || CLANG_VERSION >= 130000
Do you remember what kind of issues pahole/BTF have for
< 9.0 gcc and < 13.0 clang?
