On Thu, Aug 17, 2023 at 04:35:26PM +0200, Daniel Borkmann wrote: > On 8/17/23 6:01 AM, David Vernet wrote: > > 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. > > Urgh, to restrict BPF syscall with such `depends on` would be super ugly. Why > can't we just move this boilerplate behind a macro instead of copying this > everywhere? For example the below on top of your patch builds just fine on my > side: > > diff --git a/include/linux/btf.h b/include/linux/btf.h > index df64cc642074..6a873a652001 100644 > --- a/include/linux/btf.h > +++ b/include/linux/btf.h > @@ -83,6 +83,16 @@ > */ > #define __bpf_kfunc __used noinline > > +#define __bpf_kfunc_start \ > + __diag_push(); \ > + __diag_ignore_all("-Wmissing-prototypes", \ > + "Global functions as their definitions will be in vmlinux BTF"); \ > + __diag_ignore_all("-Wmissing-declarations", \ > + "Global functions as their definitions will be in vmlinux BTF"); > + This will not solve the robot's compain, as it fails on gcc7. The __diag_ignore_all for gcc is defined as #if GCC_VERSION >= 80000 #define __diag_GCC_8(s) __diag(s) #else #define __diag_GCC_8(s) #endif #define __diag_ignore_all(option, comment) \ __diag_GCC(8, ignore, option) so adding more __diag_ignore_all's will not do anything. This is better to patch __diag_ignore_all to include older gcc versions if anybody needs them. > +#define __bpf_kfunc_end \ > + __diag_pop(); > + > /* > * Return the name of the passed struct, if exists, or halt the build if for > * example the structure gets renamed. In this way, developers have to revisit > diff --git a/net/core/filter.c b/net/core/filter.c > index c2b32b94c6bd..08dd0dd710dd 100644 > --- a/net/core/filter.c > +++ b/net/core/filter.c > @@ -11724,11 +11724,7 @@ bpf_sk_base_func_proto(enum bpf_func_id func_id) > return func; > } > > -__diag_push(); > -__diag_ignore_all("-Wmissing-prototypes", > - "Global functions as their definitions will be in vmlinux BTF"); > -__diag_ignore_all("-Wmissing-declarations", > - "Global functions as their definitions will be in vmlinux BTF"); > +__bpf_kfunc_start > __bpf_kfunc int bpf_dynptr_from_skb(struct sk_buff *skb, u64 flags, > struct bpf_dynptr_kern *ptr__uninit) > { > @@ -11754,7 +11750,7 @@ __bpf_kfunc int bpf_dynptr_from_xdp(struct xdp_buff *xdp, u64 flags, > > return 0; > } > -__diag_pop(); > +__bpf_kfunc_end > > int bpf_dynptr_from_skb_rdonly(struct sk_buff *skb, u64 flags, > struct bpf_dynptr_kern *ptr__uninit) > > Thanks, > Daniel
