Re: [PATCH v2 bpf-next 2/2] bpf: Add __bpf_hook_{start,end} macros

[Jiri Olsa <olsajiri@gmail.com>]

On Tue, Oct 31, 2023 at 02:56:25PM -0700, Dave Marchevsky wrote:
> Not all uses of __diag_ignore_all(...) in BPF-related code in order to
> suppress warnings are wrapping kfunc definitions. Some "hook point"
> definitions - small functions meant to be used as attach points for
> fentry and similar BPF progs - need to suppress -Wmissing-declarations.
> 
> We could use __bpf_kfunc_{start,end}_defs added in the previous patch in
> such cases, but this might be confusing to someone unfamiliar with BPF
> internals. Instead, this patch adds __bpf_hook_{start,end} macros,
> currently having the same effect as __bpf_kfunc_{start,end}_defs, then
> uses them to suppress warnings for two hook points in the kernel itself
> and some bpf_testmod hook points as well.
> 
> Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
> Cc: Yafang Shao <laoar.shao@gmail.com>

Acked-by: Jiri Olsa <jolsa@kernel.org>

jirka

> ---
> 
> This patch was added in v2 in response to convo on v1's thread.
> 
>  include/linux/btf.h                                   | 2 ++
>  kernel/cgroup/rstat.c                                 | 9 +++------
>  net/socket.c                                          | 8 ++------
>  tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c | 6 ++----
>  4 files changed, 9 insertions(+), 16 deletions(-)
> 
> diff --git a/include/linux/btf.h b/include/linux/btf.h
> index dc5ce962f600..59d404e22814 100644
> --- a/include/linux/btf.h
> +++ b/include/linux/btf.h
> @@ -92,6 +92,8 @@
>  			  "Global kfuncs as their definitions will be in BTF")
>  
>  #define __bpf_kfunc_end_defs() __diag_pop()
> +#define __bpf_hook_start() __bpf_kfunc_start_defs()
> +#define __bpf_hook_end() __bpf_kfunc_end_defs()
>  
>  /*
>   * Return the name of the passed struct, if exists, or halt the build if for
> diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c
> index d80d7a608141..c0adb7254b45 100644
> --- a/kernel/cgroup/rstat.c
> +++ b/kernel/cgroup/rstat.c
> @@ -156,19 +156,16 @@ static struct cgroup *cgroup_rstat_cpu_pop_updated(struct cgroup *pos,
>   * optimize away the callsite. Therefore, __weak is needed to ensure that the
>   * call is still emitted, by telling the compiler that we don't know what the
>   * function might eventually be.
> - *
> - * __diag_* below are needed to dismiss the missing prototype warning.
>   */
> -__diag_push();
> -__diag_ignore_all("-Wmissing-prototypes",
> -		  "kfuncs which will be used in BPF programs");
> +
> +__bpf_hook_start();
>  
>  __weak noinline void bpf_rstat_flush(struct cgroup *cgrp,
>  				     struct cgroup *parent, int cpu)
>  {
>  }
>  
> -__diag_pop();
> +__bpf_hook_end();
>  
>  /* see cgroup_rstat_flush() */
>  static void cgroup_rstat_flush_locked(struct cgroup *cgrp)
> diff --git a/net/socket.c b/net/socket.c
> index c4a6f5532955..cd4d9ae2144f 100644
> --- a/net/socket.c
> +++ b/net/socket.c
> @@ -1685,20 +1685,16 @@ struct file *__sys_socket_file(int family, int type, int protocol)
>   *	Therefore, __weak is needed to ensure that the call is still
>   *	emitted, by telling the compiler that we don't know what the
>   *	function might eventually be.
> - *
> - *	__diag_* below are needed to dismiss the missing prototype warning.
>   */
>  
> -__diag_push();
> -__diag_ignore_all("-Wmissing-prototypes",
> -		  "A fmod_ret entry point for BPF programs");
> +__bpf_hook_start();
>  
>  __weak noinline int update_socket_protocol(int family, int type, int protocol)
>  {
>  	return protocol;
>  }
>  
> -__diag_pop();
> +__bpf_hook_end();
>  
>  int __sys_socket(int family, int type, int protocol)
>  {
> diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> index a5e246f7b202..91907b321f91 100644
> --- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> +++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> @@ -39,9 +39,7 @@ struct bpf_testmod_struct_arg_4 {
>  	int b;
>  };
>  
> -__diag_push();
> -__diag_ignore_all("-Wmissing-prototypes",
> -		  "Global functions as their definitions will be in bpf_testmod.ko BTF");
> +__bpf_hook_start();
>  
>  noinline int
>  bpf_testmod_test_struct_arg_1(struct bpf_testmod_struct_arg_2 a, int b, int c) {
> @@ -335,7 +333,7 @@ noinline int bpf_fentry_shadow_test(int a)
>  }
>  EXPORT_SYMBOL_GPL(bpf_fentry_shadow_test);
>  
> -__diag_pop();
> +__bpf_hook_end();
>  
>  static struct bin_attribute bin_attr_bpf_testmod_file __ro_after_init = {
>  	.attr = { .name = "bpf_testmod", .mode = 0666, },
> -- 
> 2.34.1
> 
>