Messages in this thread Patch in this message | | | Subject | Re: [PATCH bpf-next] bpf: Disable -Wmissing-declarations for globally-linked kfuncs | From | Daniel Borkmann <> | Date | Thu, 17 Aug 2023 16:35:26 +0200 |
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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@linux.dev> 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@intel.com/ >>> >>> 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"); + +#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
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