On Wed, Aug 16, 2023 at 08:48:16PM -0700, 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 It seems prudent to formally declare minimum compiler versions. Though modern gcc and clang also support -Wmissing-declarations, so maybe we should merge this patch regardless? Just unfortunate to have to add even more boilerplate just to get the compiler off our backs.
